# Impact of test speed on the thermomechanical behavior of various types of geomembranes

Hamza Tahir, Guillaume Stoltz, Guillaume Veylon, Laurent Peyras

► To cite this version:

Hamza Tahir, Guillaume Stoltz, Guillaume Veylon, Laurent Peyras. Impact of test speed on the thermomechanical behavior of various types of geomembranes. Geotextiles and Geomembranes, 2025, 53 (6), pp.1588-1599. 10.1016/j.geotexmem.2025.08.002. hal-05462983

HAL Id: hal-05462983

https://amu.hal.science/hal-05462983v1

Submitted on 16 Jan 2026

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
# Impact of test speed on the thermo-mechanical behavior of various types of geomembranes

Hamza TAHIR¹*, Guillaume STOLTZ¹, Guillaume VEYLON¹, and Laurent PEYRAS¹

¹INRAE, Aix Marseille Université, RECOVER, Aix-en-Provence, France

* Corresponding author

E-mail address: hamza.tahir@inrae.fr (H.Tahir).

**Abstract:** Geomembranes in hydraulic structures are often in exposed conditions; the ambient temperature can vary significantly and hence influence their mechanical behavior. To determine their tensile behavior at various temperatures, unidirectional tensile tests can be performed in temperature-controlled chambers. However, the test speed recommended by the main standards is high. Considering the elasto-visco-plastic behavior of geomembranes, the test speed has a double effect; the first comes from the viscous component and the second comes from temperature variation, due to the self-heating of the tested specimen during test. This study aims to investigate the effect of the test speed on the mechanical behavior of various geomembranes by decoupling the viscous effect and the self-heating effect. Through various unidirectional tensile tests performed on a wide range of test speeds, from 0.01 mm/min to 500 mm/min. It was found that for various tested geomembranes (HDPE, EPDM, PVC, FPO, Bituminous), the higher the test speed, the greater the tensile force at various strain levels and the greater the change in internal temperature of the specimen. Regarding the temperature effect, it was shown that for test speeds less than or equal to 10 mm/min, no self-heating of the specimen was observed for all geomembranes.
# 1 Introduction

From water conservation to waste containment, geomembranes are polymeric or bituminous materials that play a vital role in many engineering and environmental applications. Several studies considering the mechanical resistance of geomembranes show that temperature is one of the most important environmental elements that affects the performance of geomembranes, especially their tensile characteristics (Noval, 2015a; Zhang and Yan, 1993; Zhang et al., 2021). As highlighted by Cazzuffi et al. (2010), design of the geomembrane shall be made taking into consideration the environmental factors involved, such as, extreme temperatures and exposure to the environment. Zhang et al. (2021) tested a plasticized Polyvinyl Chloride geomembrane (PVC-P) under uniaxial tensile conditions at different ambient temperatures, ranging from -40°C to 60°C. The results showed that the strain interval for which the stress-strain curve is linear reduces and the Young's modulus increases, with decreasing temperature. On the other hand, the opposite impact is seen as the temperature rises. At low temperatures, Hsuan et al. (2008) found that generally for most of the geomembranes, their brittleness increased while flexibility decreased. According to Giroud (1995), changes in the surrounding temperature caused the plasticizers in the PVC-P geomembranes to be depleted, which caused the material to contract and subsequently compromise its flexibility. Rowe et al. (2009) exposed High Density Polyethylene (HDPE) geomembranes to a range of ambient temperatures in their investigation and found that their durability decreased with increasing temperature. Temperature affects the interfacial shear strength between geomembrane and geotextile, as shown by Akpinar and Benson (2005). These studies show that temperature has the ability to modify the mechanical response of geomembranes and hence this dependency should be taken into consideration while designing a geomembrane system.
Most of the geomembranes, especially those made of thermoplastic polymers, such as PVC-P, HDPE and Polypropylene (FPO), generally behave as elastic or viscoelastic material at small deformations, but at large deformations, they demonstrate elasto-visco-plastic behavior, based on macroscopic experimental observations (Shen et al., 2019a). Due to their elasto-visco-plastic behavior, these geomembranes demonstrate test speed dependency in their tensile behavior (stress-strain characteristics). Merry and Bray (1997) tested HDPE geomembranes of 1 and 1.5 mm thickness at different strain rates in multiaxial tension. They showed that both the initial Young's modulus and maximum stress decrease with a decrease in the strain rate. They also showed that a strain rate of 10⁻⁶ %/min might be used as a conservative estimate for a field application, while a laboratory tensile test is typically carried out at a strain rate of 1%/min (Merry and Bray, 1997). Lamri et al. (2020) studied the effects of strain rate and temperature on the mechanical behavior of a 3 mm thick HDPE geomembrane. The tests were conducted at two temperatures, -20 and 20°C, with strain rates varying from 0.001 to 100 seconds⁻¹. They found that when the temperature increases, the viscosity is significantly reduced. They also observed that the material behaves stiffer (Young's modulus increases) with an increasing strain rate (Lamri et al., 2020). Akel et al. (2025) tested a 3 mm thick transparent PVC-P geomembrane at several test speeds and found that the Young's modulus, rupture stress and rupture strain increases with increasing test speed. These studies show that while designing a geomembrane lining system, apart from the consideration of the effect of temperature, the viscous behavior of the geomembranes that influences the long-term deformation should also be well considered.

Specific studies on the behavior of thermoplastic polymers also suggest that temperature and strain rate have an impact on their mechanical response (Boyce et al., 1994; Chen et al., 2002, 2016; Hine et al., 2005). Temperature has a major effect on the yield stress and elastic modulus of thermoplastic polymers. As the temperature increases, amorphous chains become significantly more mobile, especially in the rubber-glass transition zone. The yield stress and elastic modulus drastically drop as the polymers transform from the
glassy to the rubbery state. Certain amorphous polymers, like polycarbonate and polymethylmethacrylate, exhibit distinctly different stress-strain responses in their glassy and rubbery phases (Srivastava et al., 2010). Furthermore, a material's temperature is influenced by its deformation. Energy dissipation from viscoplastic flow causes thermoplastic polymers to self-heat (Maurel-Pantel et al., 2015; Ovalle Rodas et al., 2014). Hence, the strain rate affects the viscoplastic flow behavior and yielding of thermoplastic polymers. The increase of strain rate leads to continuous hardening after yielding. Meanwhile, the self-heating phenomena is also influenced by the strain rate (Maurel-Pantel et al., 2015). This means that during deformation, hardening (which is affected by strain rate) and softening (which is caused by damage and self-heating) compete with one another (Shen et al., 2019a). Zanzinger et al. (2023) investigated the influence of testing temperature and cross-head speed on the strain hardening behavior of various HDPE geomembranes, with molecularly different PE grades. They observed linear correlation between strain hardening modulus and testing temperature as well as logarithm of cross-head speed. However, they found that the linear correlation with the logarithmic cross-head speed holds up to speeds of about 7 mm/min. Thermography measurements demonstrated that intrinsic material heating during traction test is the cause of disparities in the linear correlation between strain hardening modulus and logarithmic cross-head speed, while material coloring has a negligible impact (Zanzinger et al., 2023).

Thermal cameras have been used in multiple studies to measure temperature during uniaxial tensile testing (Jordan et al., 2020; Lin et al., 2016; Shen et al., 2019b). However, these studies are limited to polymers that are not used for geomembrane production, such as polycarbonate (PC) and polyamide 6. Furthermore, there are no studies available on the effect of test speed on the tensile behavior of all different types of geomembranes, and in particular concerning bituminous geomembranes or polymeric geomembranes such as PVC, EPDM, FPO, and reinforced polymeric geomembranes. The available studies are mainly focused on high-density polyethylene geomembranes (HDPE) or rather on polymers that are not commonly installed on hydraulic structures. At last and until now, the viscous behavior and especially,
the influence of the internal temperature on the viscous behavior for various type of geomembranes is
not well addressed.

This experimental study investigates the tensile behavior of various types of geomembranes under different test speeds and examines how the internal temperature of these geomembranes changes during these uniaxial tensile tests to determine if this phenomenon can solely explain the change in tensile behavior at different test speeds.

## 2 Methodology

### 2.1 Uniaxial tensile apparatus

The experimental setup consisted of a 10 kN uniaxial tensile testing machine combined with a video extensometer to record the elongation between two marks drawn on the specimen (Figure 1). The extensometer was aligned with the specimen, clamped in the tensile machine, using a laser-leveling device. The tensile machine is capable of testing the specimens at test speeds ranging from 0.01 mm/min to 500 mm/min. The various geomembranes were tested at the test speeds of 0.01, 0.1, 1, 10, 100 and 500 mm/min. For the lowest test speed of 0.01 mm/min, considering that a tensile test can last more than one month, for technical reasons related to the use of the tensile machine, the tests at this speed were carried out up to a maximum elongation of 250%. Although, if we look at the specifications, in terms of test speed, of the main ASTM and European standards on bituminous and polymeric geomembranes (see Table 1), we see that the lowest test speed is that of the ASTM D4885-21 standard (concerning geomembranes tested by wide strips), with a test speed value of 10 mm/min. All other test standards impose a test speed greater than or equal to 50 mm/min. In this study, the minimum test speed used is three orders of magnitude smaller than the one of the ASTM D4885-21 standard (10 mm/min). All tests were conducted in a closed and regulated temperature environment.
**Table 1** gives the tensile test specifications in terms of temperature and hygrometry for the most commonly used ASTM and European tensile-strength testing standards for geomembranes. For this study, all tests were carried out at a temperature of 23 ± 2°C and a humidity of 50 ± 10%, ambient conditions of the main European standards (EN 12311-1/2 and EN 17323).

<table><caption>**Table 1.** Specifications for the tensile testing of geomembranes (GMBs) in various standards</caption><thead><tr><td>Standard</td><td>Concerned material</td><td>Temperature (°C)</td><td>Relative humidity (%)</td><td>Test speed (mm/min)</td></tr></thead><tbody><tr><td>NF EN 12311-1</td><td>Bitumen sheets for roof waterproofing</td><td>23 ± 2</td><td>50 ± 20</td><td>100</td></tr><tr><td>NF EN 12311-2</td><td>Plastic and rubber sheets for roof waterproofing</td><td>23 ± 2</td><td>50 ± 5</td><td>100</td></tr><tr><td>NF EN 17323</td><td>Polymeric geosynthetic barriers</td><td>23 ± 2</td><td>50 ± 10</td><td>100</td></tr><tr><td>ASTM D7275 – 07 (Reapproved 2012)</td><td>Bituminous GMBs</td><td>21 ± 2</td><td>60 ± 10</td><td>50</td></tr><tr><td>ASTM D7003/D7003M – 03 (Reapproved 2021)</td><td>Reinforced GMBs</td><td>21 ± 2</td><td>60 ± 10</td><td>300</td></tr><tr><td>ASTM D6693/D6693M – 20</td><td>Non-reinforced polyethylene (PE) and non-reinforced flexible polypropylene (FPO) GMBs</td><td>21 ± 2</td><td>-</td><td>50 for PE and 500 for FPO</td></tr><tr><td>ASTM D4885 – 01 (Reapproved 2023)</td><td>Synthetic GMBs (Wide Strip Tensile Method)</td><td>21 ± 2</td><td>60 ± 10</td><td>10</td></tr></tbody></table>

## 2.2 Thermal infrared camera

The change in internal temperature of specimens during the uniaxial tensile testing was measured using a FLIR-T62101 infrared thermal camera (Figure 1). The precision of the camera measurements, as documented by the manufacturer, is ±2 K. It has a sharp thermal resolution at 76,800 pixels (320*240 pixel) for solid accuracy from farther away. Moreover, it has a high temperature range (-20 K to 650 K) and is capable of recording video at a frame rate of 60 Hz.

## 2.3 Specimens

The test specimens, except for bituminous geomembrane, conform to European standards and are dumb-bell shaped (NF EN 17323, 2020). The test specimen has a total length of 160 mm while the narrow portion
is 33 mm in length. The distance between the grips of the machine is 80 mm. The same specimen shape was considered for the PVC R geomembrane (see Table 2), which includes an internal reinforcement mesh, although the EN 17323 standard recommends a rectangular shape for this type of geomembrane. The choice is justified for comparison purposes between all polymeric geomembranes.

The test specimens for bituminous geomembrane conform to ASTM standards and are dumb-bell shaped (ASTM D7275 – 07, 2012). The ASTM standard was used because the European standard (EN 12311-1) use a rectangular specimen, which is considerably different in dimensions compared to the specimens of the other tested materials. The total length of the specimen is 125 mm and the distance between the grips of the machine is 60 mm.

The distance between the two marks, marked on the narrower portion of the specimens, is 25 mm for polymeric geomembranes and 50 mm for bituminous geomembranes. For geomembranes with dark background such as black, marks were made using a white permanent marker. Conversely, for white or light-colored geomembranes, the marks were made with a black permanent marker.

It should be noted that the European standard EN 17323 considers the total elongation of the specimen for HDPE geomembranes instead of elongation between the two marks, the latter being used for all other polymeric geomembranes. This is because the HDPE specimens extensively elongate and undergo necking, thus the shape of the marks elongate considerably as well. This makes it difficult for the extensometer to track the marks until rupture of the specimen. The process thus becomes time consuming but despite this challenge, we were successfully able to calculate the elongation between the two marks until rupture.

Hence for a consistent comparison between all the geomembranes, we will be using the results from the extensometer (elongation between the marks), instead of total elongation.
<figure><img src="image_2.png" /><figcaption>**Figure 1.** Test setup</figcaption></figure>

## 2.4 Materials

Several different types of geomembranes were tested as described in **Table 2**. Among the tested geomembranes, there are four different types of homogeneous geomembranes (HDPE, EPDM, PVC, FPO), one reinforced geomembrane (PVC R) and one composite geomembrane (PVC G). A homogeneous geomembrane refers to a geomembrane that is made of a single, uniform polymeric material without reinforcement layers or composite structures, and without textured or structured surface. A bituminous geomembrane, composed of a glass fleece/reinforcement mat, a non-woven polyethylene terephthalate (PET) geotextile and an elastomeric bitumen binder, was also tested. One face of this geomembrane was sandblasted and the other face was covered by a polyester film. These geomembranes were selected because they are commonly installed on reservoirs around the world.
<table><caption>**Table 2.** List of tested geomembranes</caption><thead><tr><td>Material</td><td>Thickness of the geomembrane component only (mm)</td><td>Legend for figures</td></tr></thead><tbody><tr><td>Polypropylene (FPO)</td><td>1.2</td><td>FPO 1.2 mm</td></tr><tr><td>Ethylene propylene diene monomer (EPDM)</td><td>1.5</td><td>EPDM 1.5 mm</td></tr><tr><td>Polyvinyl chloride (PVC)</td><td>1.5</td><td>PVC 1.5 mm</td></tr><tr><td>Polyvinyl chloride reinforced with mesh (PVC R)</td><td>1.2</td><td>PVC 1.2mm R</td></tr><tr><td>Polyvinyl chloride with glued geotextile (PVC G)</td><td>1.5</td><td>PVC 1.5 mm G</td></tr><tr><td>High-density polyethylene (HDPE)</td><td>1.5</td><td>HDPE 1.5 mm</td></tr><tr><td>Bitumen</td><td>4</td><td>Bitumen 4 mm</td></tr></tbody></table>

# 3 Results

## 3.1 Tensile behavior

**Figure 2** shows the variation of tensile force for the various geomembranes at different percentage of elongation (also called engineering strain, $\Delta L/L_0$), with the change in test speed. All the figures on the left are drawn until 200% elongation; this specific percentage of elongation is commonly used in standards to define the tensile behavior of geomembranes.

<figure><img src="image_3.png" /></figure>

1a

<figure><img src="image_4.png" /></figure>

1b
EPDM 1.5 mm

<figure><img src="image_5.png" /><figcaption>2a</figcaption></figure>

EPDM 1.5 mm

<figure><img src="image_6.png" /><figcaption>2b</figcaption></figure>

PVC 1.5 mm

<figure><img src="image_7.png" /><figcaption>3a</figcaption></figure>

PVC 1.5 mm

<figure><img src="image_8.png" /><figcaption>3b</figcaption></figure>

PVC 1.2 mm R

<figure><img src="image_9.png" /><figcaption>4a</figcaption></figure>

PVC 1.2 mm R

<figure><img src="image_10.png" /><figcaption>4b</figcaption></figure>
<figure><img src="image_11.png" /><figcaption>5a</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>5b</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>6a</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>6b</figcaption></figure>

<figure><img src="image_15.png" /><figcaption>7a</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>7b</figcaption></figure>

**Figure 2.** Tensile force characteristics of various types of geomembranes under various test speeds

From Figure 2, it is generally observed that for all the geomembranes, for a given elongation, the tensile force increases with the increase in test speed.
For the FPO geomembrane, a linear/elastic tensile response at lower elongation is observed, followed by a plastic deformation until 200% elongation (a significant yield point is observed indicating the onset of plastic deformation). This is followed by a hardening effect until rupture of the specimen. At 20% elongation, an increase in the tensile force of 148% is observed when the test speed varies from 0.01 mm/min to 500 mm/min. At 200% elongation, an increase of 90% of tensile force is observed as we move from the lowest to the highest test speed.

For the EPDM geomembrane, almost a linear deformation until rupture is observed. The tensile force at lower elongation (<40% elongation) is not very sensitive to the variation in test speed but at 200% elongation, the tensile force increases by 35% as the test speed is increased from 0.01 mm/min to 500 mm/min.

For the PVC geomembrane, a linear deformation is observed. The linearity of the tensile curve increases as the test speed is decreased. The PVC GMB lack a distinct yield point due to its amorphous structure. For all levels of elongation, an important influence of the test speed on the tensile force is observed. For example, the increase in the tensile force at 200% elongation as we pass from the lowest to the highest test speed is 109%.

The PVC R geomembrane exhibits a higher initial Young's modulus and ultimate strength, compared to a simple PVC GMB, due to the reinforcing layer of polyethylene terephthalate (PET). The reinforcement restricts deformation, raising the modulus and reducing elongation at maximal tensile resistance compared to unreinforced PVC. A first peak in the tensile force curves is observed which corresponds to the rupture of the reinforced fibers/PET (Polyethylene terephthalate) reinforcement present in the specimens. It can be observed that this peak occurs between 10-20% elongation for the higher test speeds (10, 100 and 500 mm/min), while it occurs between 25-50% elongation for the lower test speeds (0.01, 0.1 and 1 mm/min). An increase of 154% in the tensile force at first peak is observed as the test speed is
increased from 0.01 mm/min to 500 mm/min. The second peak at the end of the test corresponds to the rupture of the PVC barrier layer.

The PVC G geomembrane shows a composite behavior, with the initial region reflecting the combined stiffness of PVC and geotextile. It has a higher modulus compared to a simple PVC GMB due to the contribution from the glued geotextile. A first peak in the tensile force curves is observed which corresponds to the rupture of the glued geotextile (rupture of nonwoven backing). It can be observed that this peak occurs between 55-80% elongation for the higher test speeds (10, 100 and 500 mm/min), while it occurs between 75-95% elongation for the lower test speeds (0.01, 0.1 and 1 mm/min). An increase of 80% in the tensile force at first peak is observed as the test speed is increased from 0.01 mm/min to 500 mm/min. Similar to the PVC R geomembrane, the second peak at the end of the test corresponds to the rupture of the PVC barrier layer. The tensile behavior of the PVC G GMB is strongly driven by the highly variable tensile behavior of the glued geotextile. Thus, to reduce the high uncertainty in the behavior of the PVC G specimens, further tensile tests needs to be conducted.

For the HDPE geomembranes, a first peak (corresponding to necking and yield point of the specimen) at elongation lower than 20% is observed, followed by a strain softening. A distinct peak (distinct yield point at low strain (~12%)) and strain softening are not observed for lower test speeds of 0.1 mm/min and 0.01 mm/min. It is followed by a plastic response and a strain hardening afterwards until rupture. At the first peak (yield point), an increase in the tensile force of 91% is observed when the test speed varies from 0.01 mm/min to 500 mm/min. At 200% elongation, an increase of 53% of tensile force is observed as we move from the lowest to the highest test speed.

Lastly, for the bituminous geomembrane, the initial deformation is mainly due to the deformation of the glass reinforcement and bitumen binder acting together. The modulus here is high. The first peak (around 4% elongation) in the tensile force – elongation curve corresponds to the rupture of the glass mat. An
increase of 84% in the tensile force at first peak is observed as the test speed is increased from 1 mm/min to 500 mm/min. The first force peak is followed by the stress-strain behavior in the PET geotextile acting together with the bitumen binder; the modulus here is lower than the modulus in the elastic region. The second peak at the end of the test corresponds to the failure of the non-woven PET geotextile. A distinct first peak followed by the stress-strain behavior in the PET geotextile are not observed for lower test speeds of 0.1 mm/min and 0.01 mm/min. The main issue encountered at such a lower test speed is that the material starts deforming at the grips, at all settings of the grip's force. As a result, two layers are formed, an outer layer holding well to the grips and an inner layer sliding/shearing through the outer layer. Hence, the material keeps elongating without taking any load (no rupture). This effect is observed at the lower fixed grip of the uniaxial tensile machine and is extremely evident for a test speed of 0.01 mm/min, as can be seen from **Figure 3**. Several clamping pressures were tested to avoid this problem. In fact, as soon as the clamping pressure becomes low enough to avoid creep shear of the bituminous geomembrane specimen, the specimen then slides completely outside the grip. Thus, it was not possible to find a grip clamping pressure that would allow the bituminous geomembrane specimens to be tested in pure unidirectional tension at the lowest test speed of 0.01 and 0.1 mm/min.

<figure><img src="image_17.png" /><figcaption>**Figure 3.** Deformation of bituminous geomembrane specimens at lower test speeds</figcaption></figure>
## 3.2 Internal temperature measurement

**Figure 4** shows the change in internal temperature of the specimens at various levels of elongation (percentage of elongation), for the different tested test speeds. These levels of elongation are chosen such that they cover all the regions of the typical tensile behavior charts of these materials and hence they can be analyzed with respect to the corresponding tensile curves shown in **Figure 2**.

<figure><img src="image_18.png" /><figcaption>**Figure 4.** Change in internal temperature of various types of geomembranes at various percentage of elongation</figcaption></figure>

It can be generally observed that for a given percentage of elongation and for a specific material, the change in internal temperature increases with an increase in the test speed. For example, at 20% elongation for the PVC R geomembrane, the change in internal temperature is 0, 0, 3.8 and 9.6 K for the test speeds of 1, 10, 100 and 500 mm/min respectively. Similarly, for the HDPE geomembrane at 200%
elongation, the observed change in internal temperature is 0.4, 2.2, 15.2 and 26.5 K for the test speeds of 1, 10, 100 and 500 mm/min respectively.

Furthermore, generally for a specific material at a fixed test speed, the change in internal temperature is directly related to the percentage of elongation. The greater the percentage of elongation, the greater is the change in internal temperature in general. For example, for the PVC R geomembrane tested at 100 mm/min, the change in internal temperature is 0, 3.8, 5.8 and 7 K at the elongations of 10, 20, 100 and 200% respectively. Similarly, for the HDPE geomembrane tested at 500 mm/min, the observed change in internal temperature is -0.1, 1, 5.3 and 26.5 K at the elongations of 10, 20, 100 and 200% respectively.

A particular observation about the bituminous geomembrane can be made that the change in internal temperature is always less than or equal to 0.6 K at any level of elongation and/or at any test speed.

To make the analysis simpler, another approach was also used that includes comparing the internal temperature just before the rupture of the specimen with the internal temperature just before the start of the test. As the internal temperature at the start of the test is almost homogeneous across the specimen, hence the mean internal temperature along the thin portion of the specimen was used. For the reference internal temperature just before the rupture, as the internal temperature of the specimen is not uniform and can be highly variable, the maximum internal temperature in the thin portion of the specimen was used (which is the zone of rupture). Hence, the change in the internal temperature of the specimen during the test is the difference between the above-mentioned two reference temperatures (maximum temperature just before rupture temperature – mean initial temperature). **Figure 5** shows this change in the internal temperature during the test for the various geomembranes tested at different test speeds.
<figure><img src="image_19.png" /><figcaption>**Figure 5.** Change in internal temperature of various types of geomembranes during tensile testing, under various test speeds</figcaption></figure>

A similar general trend, compared to **Figure 4**, of increase in the internal temperature with the increase in test speed is observed here. The change in internal temperature can be as high as 37.2 K, as observed for the HDPE geomembrane tested at the test speed of 500 mm/min.

For the bituminous geomembrane, the change of internal temperature is 0.1 to 1.3 K, at all tested test speeds. Thus, it can be concluded that the internal temperature change is insignificant for the bituminous geomembrane, irrespective of the test speed. Hence, excluding the bituminous geomembrane, the change in internal temperature for the rest of the geomembranes is 3.3 to 11.5 K at 100 mm/min and 11.5 to 37.2 K at 500 mm/min. Thus, it can be concluded that the change in internal temperature for all the geomembranes, except the bituminous geomembrane, is significant at the test speeds of 100 and 500
mm/min. It should be kept in mind that a test speed of 500 mm/min might be rarely used (like in the case of ASTM D6693/D6693M - 20, for the testing of FPO GMBs) but a test speed of 100 mm/min is commonly used for the tensile testing of various types of geomembranes (especially in many European standards).

Furthermore, for all the geomembranes, the change in internal temperature is less than 1 K (0.1 to 0.6 K) for the test speed of 1 mm/min, while it is less than 2 K (0.5 to 1.7 K) for the test speed of 10 mm/min.

Thus, it can be concluded that the change in internal temperature for all the geomembranes is insignificant at the test speeds of 1 and 10 mm/min.

# 4 Discussion

## 4.1 Correlation between tensile strength and test speed

**Figure 6** shows the variation of the Young's modulus for the various test speeds. The Young's modulus is calculated from the initial secant drawn between 0% and 5% elongation (engineering strain) for all the geomembranes, except bituminous geomembrane (0% to 3%). This limit was chosen considering the range of linear stress-strain relationship for all the geomembranes. Furthermore, it allows using the initial specimen area for stress calculation as the cross-section variation at 5% elongation might be considered negligible. It is important to mention that method D as per EN 17323 for non-reinforced GMBs calculates Young's modulus between 1-2% of elongation at 1 mm/min (using 10 mm wide specimen as compared to 6 mm in our case). In our study, if the Young's modulus is assessed in the same elongation range, i.e. between 1 and 2%, this induces significant measurement uncertainties for higher test speeds, and in particular for the speeds of 100 and 500 mm/min. Our analysis led us to evaluate the Young's modulus between 0 and 5% of elongation, in order to minimize measurement uncertainties at very small elongations when the test speed is high. Furthermore, for the composite geomembranes, that is to say those that incorporate a reinforcing element, the total force in the specimen and the total area of the specimen were used to calculate the Young's secant modulus, without accounting for local stress
heterogeneity. Thus, for these geomembranes, the Young's modulus corresponds to a mechanical property of the entire composite material, although the reinforcing element contributes more to the tensile resistance of the specimen (until its rupture) as compared to the polymeric sheet.

The plotted trend curves correspond to a relationship of type E = A log v/v0 + B, with 'E' the Young's modulus, 'v' the test speed and 'A and B' constants. The coefficient of determination 'R²' of each of the trend lines are displayed in **Figure 6**. The closer this coefficient R² is to 1, the stronger the relationship between Young's modulus and the test speed.

<figure><img src="image_20.png" /><figcaption>**Figure 6.** Variation of Young's Modulus of various types of geomembranes under various test speeds and logarithmic trend lines</figcaption></figure>

It is clear from the **Figure 6** that the Young's modulus generally increases with an increasing test speed. The change in Young's modulus between the tests carried out at 0.01 and 500 mm/min is 586%, 333%, 275%, 223%, 180% and 78% for the PVC, PVC G, FPO, PVC R, HDPE and EPDM geomembranes respectively. The increase in Young's modulus for the bituminous geomembrane is 172% between the tests carried out at 1 and 500 mm/min. The correlation by a logarithmic relationship between Young's modulus and test
speed is strong for the FPO, PVC, bituminous and HDPE geomembranes, with values of coefficient of determination 'R²' close or superior to 0.9. The correlation for PVC R and PVC G geomembranes is medium, with values of coefficient of determination 'R²' close to 0.7. Although the results clearly show an increase in Young's modulus with test speed, many additional tests would be necessary to determine whether there is a correlation between these two parameters and estimate the associated uncertainty. The poor correlations for PVC R and PVC G geomembranes may be caused by the variations of the reinforcement and geotextile backing respectively from specimen to specimen. The correlation for the EDPM geomembranes is very weak, with a determination coefficient value of 0.47, which may be caused by the similar elastic response at lower elongations, as can also be observed in **Figure 2**.

**Figure 7** shows the variation in the tensile response of all the tested geomembranes, at different levels of elongation and for all the tested test speeds. As it was done in **Figure 6**, the plotted trend curves correspond to a relationship of type $F_ε = A \log v/v_0 + B$, with ‘$F_ε$’ the tensile force at $\epsilon\%$ of elongation, ‘$v$’ the test speed and ‘A and B’ constants.

<figure><img src="image_21.png" /></figure>

a

<figure><img src="image_22.png" /></figure>

b
<figure><img src="image_23.png" /></figure>

c

<figure><img src="image_24.png" /></figure>

d

<caption>**Figure 7.** Variation of tensile force of various types of geomembranes at different percentage of elongation, under various test speeds, and logarithmic trend lines</caption>

Compared to the analysis of the effect of the test speed on the tensile strength at small elongation (**Figure 6**), the same effect is investigated here but for elongation ranging from 10 to 200% elongation. The results are analyzed and discussed for each type of geomembrane tested. For homogeneous FPO, PVC and HDPE geomembranes, it is observed that for the four levels of elongation considered, the traction force is correlated to the test speed by a logarithmic relationship, with coefficients of determination 'R²' all greater than 0.90. For the homogeneous EPDM geomembrane, a correlation is observed only for the highest elongation level, i.e. 200%, which corresponds well to the first observation made from **Figure 2**. For the PVC R geomembrane, the elongation level of 20% does not indicate a correlation between tensile force and test speed, which is explained by the reinforcement rupture zone that is located between elongations of 12 to 50% (see **Figure 2d**). This poor correlation at 20% elongation is caused by the variations of the reinforcement in the specimens, thus resulting in reinforcement rupture at a differing elongation and hence the reinforcement has already ruptured in some specimens at this point while still undergoing deformation in others. Once the reinforcement breaks, only the PVC part of the geomembrane takes up the tensile force and a correlation between tensile force and test speed is then observed for elongations of 100 and 200%, with coefficient of determination values greater than 0.9. For the PVC G geomembrane,
a correlation between tensile force and test speed can be observed for the four elongations 10, 20, 100 and 200%, with coefficient of determination values greater than 0.85. However, this observation masks the fact that the geotextile rupture occurs for elongation levels between 50 and 80% elongation (Figure 2e). In this elongation range, the correlation between tensile force and test speed is not obtained at all elongation points. For the bituminous geomembrane, a clear correlation between tensile force and test speed is observed for elongation 10 and 20%, with coefficients of determination greater than 0.95. There are no curves for elongation levels of 100 and 200%, because the geomembrane breaks at elongation levels significantly lower than 100% (Figure 2g).

**Figure 8** shows the variation of the first peak tensile force for some tested geomembranes (i.e. FPO, PVC R, PVC G, HDPE and bitumen), for all the tested test speeds. As it was done previously, the plotted trend curves correspond to a relationship of type $F_{1stpeak} = A \log v/v_0 + B$, with ‘$F_{1stpeak}$’ the tensile force at first peak, ‘$v$’ the test speed and ‘$A$ and $B$’ constants.

<figure><img src="image_25.png" /><figcaption>**Figure 8.** Variation of first peak tensile force of various types of geomembranes under various test speeds, and logarithmic trend lines</figcaption></figure>
It can be observed from **Figure 8** that the first peak tensile force generally increases with the increase in test speed. The correlation between first peak tensile force and test speed is very strong for the FPO, HDPE and bituminous geomembranes, with coefficient of determination values greater than 0.92, but is quite weak for the PVC R and PVC G geomembranes. For the PVC R and PVC G geomembranes, the tensile force at the first peak corresponds respectively to the rupture of the internal reinforcement for the PVC R geomembrane and of the geotextile for the PVC G geomembrane. In both cases, it can be assumed that the rupture of the internal reinforcement for the PVC R geomembrane and of the geotextile for the PVC G geomembrane are not sensitive to the test speed. Thus, in the graph, the observed variations of the yellow and blue points would be mainly explained by the variability of the resistance of the internal reinforcement for the PVC R geomembrane and of the geotextile for the PVC G geomembrane.

**Figure 9** shows the variation of the rupture tensile force of all the tested geomembranes, for all the tested test speeds. As it was done previously, the plotted trend curves correspond to a relationship of type $F_{rupture} = A \log v/v_0 + B$, with ‘$F_{rupture}$’ the tensile force at rupture, ‘$v$’ the test speed and ‘$A$ and $B$’ constants. It should be noted that the rupture tensile forces at the test speed of 500 mm/min are not included in this graph because of the unmeasurable uncertainty in these measurements. The considerably higher test speed results in a quicker rupture, which may not be properly captured by the data acquisition system of the video extensometer due to its limitations.
<figure><img src="image_26.png" /><figcaption>**Figure 9.** Variation of rupture tensile force of various types of geomembranes under various test speeds, and logarithmic trend lines</figcaption></figure>

It can be observed from **Figure 9** that the rupture tensile force increases with the increase in test speed. The correlation between rupture tensile force and test speed is very strong for all the tested geomembranes, with coefficient of determination values greater than 0.92, except FPO (considerable but not very strong). For the PVC R and PVC G geomembranes, where it previously (**Figure 8**) showed no correlation between the tensile force at first peak and test speed, a strong correlation is now observed, with coefficient of determination values greater than 0.92. This can be explained by the fact that the tensile force at rupture correspond to the rupture of the PVC component only, which is sensitive to test speed.

The intrinsic properties of all the tested geomembranes, calculated based upon our results, are given in **Table 3**. It should be noted that the tensile strength (kN/m) has been calculated without taking in account the reduction of the width of the specimens during the tensile tests.
<table><caption>Table 3. Intrinsic properties of the tested geomembranes</caption><thead><tr><th>GMB</th><th>Test Speed mm/min</th><th>Tensile strenght at 15% elongation (kN/m)</th><th>Tensile strenght at rupture (kN/m)</th><th>Elongation at rupture (%)</th></tr></thead><tbody><tr><td rowspan="6">FPO 1.2 mm</td><td>0.01</td><td>3.66</td><td>NA</td><td>NA</td></tr><tr><td>0.1</td><td>4.52</td><td>19.77</td><td>818.25</td></tr><tr><td>1</td><td>5.09</td><td>22.91</td><td>804.40</td></tr><tr><td>10</td><td>6.42</td><td>23.59</td><td>780.74</td></tr><tr><td>100</td><td>8.01</td><td>23.91</td><td>713.33</td></tr><tr><td>500</td><td>9.57</td><td>21.62</td><td>734.68</td></tr><tr><td rowspan="6">EPDM 1.5 mm</td><td>0.01</td><td>1.11</td><td>NA</td><td>NA</td></tr><tr><td>0.1</td><td>1.15</td><td>13.64</td><td>426.81</td></tr><tr><td>1</td><td>1.14</td><td>14.82</td><td>430.26</td></tr><tr><td>10</td><td>1.14</td><td>16.02</td><td>464.17</td></tr><tr><td>100</td><td>1.14</td><td>17.39</td><td>461.61</td></tr><tr><td>500</td><td>1.48</td><td>17.45</td><td>470.02</td></tr><tr><td rowspan="6">PVC 1.5 mm</td><td>0.01</td><td>1.27</td><td>NA</td><td>NA</td></tr><tr><td>0.1</td><td>1.68</td><td>14.34</td><td>275.27</td></tr><tr><td>1</td><td>2.04</td><td>18.03</td><td>272.59</td></tr><tr><td>10</td><td>3.08</td><td>21.62</td><td>294.23</td></tr><tr><td>100</td><td>3.96</td><td>23.62</td><td>304.22</td></tr><tr><td>500</td><td>5.28</td><td>23.95</td><td>331.40</td></tr><tr><th>GMB</th><th>Test Speed mm/min</th><th>Tensile strenght at first peak (kN/m)</th><th>Elongation at first peak (%)</th><th>Tensile strenght at rupture (kN/m)</th><th>Elongation at rupture (%)</th></tr><tr><td rowspan="6">PVC 1.2 mm R</td><td>0.01</td><td>14.46</td><td>31.73</td><td>7.29</td><td>143.60</td></tr><tr><td>0.1</td><td>26.25</td><td>46.66</td><td>8.97</td><td>108.24</td></tr><tr><td>1</td><td>17.29</td><td>38.01</td><td>12.02</td><td>216.28</td></tr><tr><td>10</td><td>19.01</td><td>18.98</td><td>14.69</td><td>233.81</td></tr><tr><td>100</td><td>24.81</td><td>15.74</td><td>15.20</td><td>247.25</td></tr><tr><td>500</td><td>36.68</td><td>18.27</td><td>15.01</td><td>47.00</td></tr><tr><td rowspan="6">PVC 1.5 mm G</td><td>0.01</td><td>13.82</td><td>83.65</td><td>10.68</td><td>189.53</td></tr><tr><td>0.1</td><td>12.75</td><td>79.64</td><td>12.99</td><td>224.43</td></tr><tr><td>1</td><td>21.04</td><td>89.87</td><td>16.78</td><td>224.05</td></tr><tr><td>10</td><td>16.91</td><td>75.63</td><td>20.45</td><td>243.36</td></tr><tr><td>100</td><td>16.47</td><td>60.39</td><td>22.44</td><td>263.93</td></tr><tr><td>500</td><td>24.92</td><td>62.13</td><td>21.05</td><td>211.19</td></tr><tr><th>GMB</th><th>Test Speed mm/min</th><th>Tensile strenght at yield (kN/m)</th><th>Elongation at yield (%)</th><th>Tensile strenght at rupture (kN/m)</th><th>Elongation at rupture (%)</th></tr><tr><td rowspan="6">HDPE 1.5 mm</td><td>0.01</td><td>16.18</td><td>21.17</td><td>NA</td><td>NA</td></tr><tr><td>0.1</td><td>18.85</td><td>19.46</td><td>37.71</td><td>609.87</td></tr><tr><td>1</td><td>22.00</td><td>17.35</td><td>41.58</td><td>611.53</td></tr><tr><td>10</td><td>25.69</td><td>11.64</td><td>43.90</td><td>659.82</td></tr><tr><td>100</td><td>29.50</td><td>10.01</td><td>46.67</td><td>660.84</td></tr><tr><td>500</td><td>30.96</td><td>5.92</td><td>38.46</td><td>616.37</td></tr><tr><td rowspan="6">Bitumen 4 mm</td><td>0.01</td><td>NA</td><td>NA</td><td>NA</td><td>NA</td></tr><tr><td>0.1</td><td>NA</td><td>NA</td><td>NA</td><td>NA</td></tr><tr><td>1</td><td>11.46</td><td>5.97</td><td>19.17</td><td>42.94</td></tr><tr><td>10</td><td>15.34</td><td>4.69</td><td>24.87</td><td>52.52</td></tr><tr><td>100</td><td>21.40</td><td>3.99</td><td>29.27</td><td>48.31</td></tr><tr><td>500</td><td>21.08</td><td>4.03</td><td>34.87</td><td>50.08</td></tr></tbody></table>
When comparing our results with some of the existing researches such as, Merry and Berry (1997), Wesseloo et al. (2004), Lamri et al. (2020), and Akel et al. (2025), similar overall trends are observed; an increase in the test speed results in the increased stiffness of the tested geomembranes (increased tensile resistance). Although exact comparisons cannot be made as the tested GMBs (across the various researches) vary in their properties, an order of magnitude is still given. When comparing our results with the results of Akel et al. (2025), at 100% elongation, an increase in the tensile force of 181% is observed for our tested PVC 1.5 mm colored GMB and 144% for their tested PVC 3 mm transparent GMB (using their force-engineering strain curve, Fig. 7, for comparison) when the test speed varies from 0.01 mm/min to 500 mm/min. At 200% elongation, an increase of 109% in the tensile force is observed in our case while 88% in their case as we move from the lowest to the highest test speed. Similarly, when comparing our results with the results of Wesseloo et al. (2004), an increase in the engineering stress of 48% is observed for our tested HDPE 1.5 mm GMB and 82% for their tested HDPE 0.2 mm GMB (using their engineering stress-engineering strain curve, Fig. 6, for comparison) when the test speed varies from 0.1 mm/min to 100 mm/min. At 200% elongation, an increase of 35% of tensile force is observed in our case while 46% in their case as we move from the lowest to the highest test speed. Thus, a general observation can be made that the percentage change observed in the resistance of a GMB increases with the reduction in its thickness and this observed change decreases as the elongation increases.

It is important to note that the width of specimen can affect the thermo-mechanical behavior of geomembranes. To consider this, wide-strip or rectangular specimen can be tested. The use of dumb-bell specimens in our case was intentional in order to reach the rupture of all the specimens (FPO specimens deformed more than 700%). Increasing the width increases the elongation at rupture, which exceeded the maximum limit of the testing apparatus for HDPE and FPO geomembrane. Nevertheless, several researchers have used narrower specimens for testing such as; Zanzinger et al. (2023) have used EN 17096:2018 for the calculation of the strain hardening modulus of various grades of PE geomembrane.
The dumb-bell specimen used has a narrower thin portion (2 mm wide) as compared to the specimen in EN 17323 (6 mm wide). Furthermore, Akel et al. (2025) used specimen similar to ours to study the rate-dependent tensile response of Polyvinyl Chloride geomembranes while Lamri et al. (2020) have used 10 mm wide HDPE specimens to investigate the effects of strain rate and temperature on the mechanical behavior of high-density polyethylene.

While the uniaxial tensile test is well adapted to represent the tensile deformations of a geomembrane laid on a steep slope, it is less suitable for representing multiaxial deformations that occur, for example, when a localized asperity forms under the geomembrane. To represent this type of multiaxial deformation, the multiaxial tensile test, or burst test, can be used. This test can be carried out according to the NF EN 14151 standard, or by the ASTM D5617-04 standard. By extension of the results presented and analyzed in this study, it can be assumed that the behavior of the geomembranes, in terms of stress-strain, evaluated by a multiaxial tensile test, will be modified if the strain rate of the test changes. This was observed by Merry and Bray (1997) for HDPE geomembranes only, with for example a significant drop of maximum stress and secant modulus when the strain rate decreases (the tested strain rate range was 10 to 0.0004%/min). For both unidirectional and multiaxial tensile tests, the effect of speed test on the stress-strain behavior of geomembranes at small deformations is of major interest to the design engineer because, as Giroud (1994) has shown, the behavior beyond the "yield point" is of little importance for the design of common geomembrane systems.

To summarize, **Section 3.1** and **Section 4.1** serves as a caution to engineers by demonstrating that the tensile curves obtained at lower test speeds are more conservative (greater factor of safety). Furthermore, these lower test speeds are more realistic to the field (geomembranes installed on dams). Thus, to warn engineers of this change in behavior, it can be recommended to use a lower test speed for the design of geomembranes. The test speed should be better adapted considering the actual field conditions and the risks of a failure.
## 4.2 Correlation between internal temperature and test speed

**Section 3.2** shows the self-heating of geomembranes during tensile tests. Over the past half century, considerable amount of research has been conducted on the mechanical behaviour of thermoplastic polymers (Barentsen and Heikens, 1973; Bax and Müssig, 2008; Kennedy et al., 1994; Mullins, 1948; Nielsen, 1969). Long, flexible chains joined by hydrogen and van der Waals bonds make up thermoplastic polymers. When a thermoplastic polymer is stretched, the rearrangement/slippage of polymer chains is one of the main mechanisms generating heat and thus internal heating of the material. Jabbari-Farouji et al. (2015) showed that the slippage of organized chains tears apart the crystalline regions which, under high stress, eventually transform into a highly oriented fibrillar structure. In addition, viscosity, involving internal resistance to chain movement and microstructure reorganization, generates energy dissipation also leading to self-heating of the material (Maurel-Pantel et al., 2015; Ovalle Rodas et al., 2014).

**Figure 10** shows the variation of change in internal temperature of all the tested geomembranes, at rupture, for all the tested test speeds. As it was done previously, the plotted trend curves correspond to a relationship of type $T_{rupture} = A \log v/v_0 + B$, with ‘$T_{rupture}$’ the internal temperature of the geomembrane specimen just before rupture, ‘$v$’ the test speed and ‘$A$ and $B$’ constants.
<figure><img src="image_27.png" /><figcaption>**Figure 10.** Variation of change in internal temperature of various types of geomembranes at rupture, under various test speeds, and logarithmic trend lines</figcaption></figure>

Table 4 shows the values of the coefficients ‘A’ and ‘B’ for all the calibrated logarithmic relationships demonstrated in Figure 6 to Figure 10.

<table><caption>**Table 4.** Values of the coefficients for all the calibrated logarithmic relationships</caption><thead><tr><th rowspan="2"></th><th colspan="2">A</th><th colspan="2">B</th><th colspan="2">A</th><th colspan="2">B</th><th colspan="2">A</th><th colspan="2">B</th><th colspan="2">A</th><th colspan="2">B</th></tr><tr><th>Young's Modulus</th><th>10% Elongation</th><th>20% Elongation</th><th>100% Elongation</th><th>200% Elongation</th><th>First Peak</th><th>Rupture</th><th>Young's Modulus</th><th>10% Elongation</th><th>20% Elongation</th><th>100% Elongation</th><th>200% Elongation</th><th>First Peak</th><th>Rupture</th><th>Young's Modulus</th><th>10% Elongation</th></tr></thead><tbody><tr><td>FPO 1.2 mm</td><td>19.3</td><td>61.7</td><td>7.4</td><td>29.9</td><td>7.3</td><td>36.3</td><td>5.9</td><td>39.0</td><td>5.7</td><td>40.3</td><td>6.8</td><td>39.5</td><td>7.9</td><td>131.3</td><td>19.3</td><td>61.7</td></tr><tr><td>EPDM 1.5 mm</td><td>0.8</td><td>7.6</td><td>0.3</td><td>5.6</td><td>0.3</td><td>8.3</td><td>1.4</td><td>27.0</td><td>3.0</td><td>51.5</td><td>-</td><td>-</td><td>7.5</td><td>89.1</td><td>0.8</td><td>7.6</td></tr><tr><td>PVC 1.5 mm</td><td>7.3</td><td>15.8</td><td>4.1</td><td>11.5</td><td>5.7</td><td>18.2</td><td>11.2</td><td>48.7</td><td>12.8</td><td>79.8</td><td>-</td><td>-</td><td>18.9</td><td>107.0</td><td>7.3</td><td>15.8</td></tr><tr><td>PVC 1.2 mm R</td><td>26.8</td><td>92.3</td><td>15.5</td><td>49.9</td><td>2.8</td><td>60.9</td><td>8.7</td><td>59.2</td><td>7.6</td><td>72.6</td><td>18.7</td><td>130.1</td><td>12.8</td><td>69.9</td><td>26.8</td><td>92.3</td></tr><tr><td>PVC 1.5 mm G</td><td>9.1</td><td>28.2</td><td>5.1</td><td>20.4</td><td>7.7</td><td>31.4</td><td>11.6</td><td>57.9</td><td>13.8</td><td>89.0</td><td>10.9</td><td>101.0</td><td>19.3</td><td>99.4</td><td>9.1</td><td>28.2</td></tr><tr><td>HDPE 1.5 mm</td><td>60.2</td><td>224.8</td><td>21.2</td><td>127.7</td><td>16.0</td><td>130.3</td><td>10.3</td><td>107.9</td><td>10.6</td><td>106.9</td><td>19.7</td><td>134.3</td><td>17.5</td><td>246.0</td><td>60.2</td><td>224.8</td></tr><tr><td>Bitumen 4 mm</td><td>22.8</td><td>31.7</td><td>87.0</td><td>294.0</td><td>102.4</td><td>340.4</td><td>-</td><td>-</td><td>-</td><td>-</td><td>98.0</td><td>293.3</td><td>126.3</td><td>484.6</td><td>22.8</td><td>31.7</td></tr></tbody></table>

It can be concluded from **Figure 10** that strong correlations can be made between the change in internal temperature of the geomembrane specimens during tensile testing and the test speed. It is worth noting that these correlations can only be made from the test speed of 10 mm/min and onwards. If lower test
speeds are considered, there correlations become weaker as insignificant change in internal temperature
was observed at lower test speeds (see **Figure 5**). Furthermore, it should be noted that the non-linearity
of the tensile curve, especially the slope of the strain-hardening part of the tensile behavior curves for
FPO, PVC and HDPE, considerably reduces when the test is carried out at a test speed of 500 mm/min, as
compared to the other tested speeds (see **Figure 2**). This may be caused by the considerably higher amount
of self-heating of the specimens observed at this speed, compared to other speeds (see **Figure 5**).

For bituminous geomembrane, the internal temperature change is insignificant at all the test speeds. The
internal temperature of bituminous geomembranes does not significantly change during a tensile test,
regardless of the test speed.

As established in **Section 3.2**, the internal temperature of geomembranes rises during the tensile tests and the degree of rise depends on the test speed i.e., generally the greater the test speed, the greater is the rise in temperature. The vast majority of mechanical energy in a uniaxial tensile test is transformed into thermal energy during loading, with the remainder being utilized partially for microstructural evolution (Haward, 1994) and hardening (Krairi and Doghri, 2014). The heat generated by the plastic work may cause the temperature of the material to rise. Since the mechanical behavior of polymers is known to be temperature dependent, a temperature increase during testing can significantly affect the mechanical response.

These experimental results also established that the change in internal temperature is significant for the
tensile tests carried out at 100 and 500 mm/min. Furthermore, the tensile test at 1 and 10 mm/min
resulted in insignificant internal temperature change. Thus, it can be concluded that the effect of test
speed on internal temperature change shows that higher test speed is not relevant for design. Instead,
tensile tests at lower test speeds allow little internal temperature rise during the experiments, that will
not result in the behavioral change of the geomembranes during testing. Hence, it serves as a caution to
engineers that if the temperature is a major concern at an installation site, it is important to consider
testing of geomembranes at a test speed of 10 mm/min or even lower.

We used the experimental data set of the study to determine whether the change in internal temperature of geomembrane specimens subjected to tensile testing could explain the change in tensile behavior when the tensile speed varied from 0.01 mm/min to 500 mm/min.

For all homogeneous geomembranes, it was shown that the test speed significantly modified the tensile
strength, regardless of the level of deformation. However, there are some specific cases, such as for the
EPDM geomembrane, for which the effect of the tensile speed is only observed at high levels of
deformation. For the PVC R and PVC G geomembranes, which respectively include an internal
reinforcement and a bonded geotextile, it was observed that this reinforcement component was not
sensitive to the test speed, whereas the PVC component alone was. Measurements of internal
temperature variations showed that the tensile test led to significant self-heating of the specimens only
from a speed of 100 mm/min. It can therefore be concluded that this self-heating effect is not the origin
of the rate dependency of the different geomembranes when they are subjected to a unidirectional tensile
test.

5 Conclusions

The paper discussed the influence of test speed on the tensile characteristics of various types of geomembranes. Tensile experiments were carried out at the test speeds of 0.01, 0.1, 1, 10, 100 and 500 mm/min along with studies on the internal temperature rise during the tensile tests carried out at the test speeds of 1, 10, 100 and 500 mm/min, using a thermal camera.
1. The test speed modifies the tensile strength of all geomembranes tested in this study, regardless of their nature: bituminous or polymeric (EPDM, HDPE, FPO and PVC). The magnitude of this effect depends on the nature of the geomembrane.

Generally, the higher the test speed, the higher is the tensile strength. The effect of the test speed on the strength of the different tested geomembranes is observed at small deformation, and in particular on the Young's modulus, at medium deformation and on the tensile strength at rupture.

2. Generally, regardless of the level of deformation, the increase in the tensile strength force 'F' as a function of the test speed 'v' can be interpreted by a logarithmic law of the form: $F = A \log v/v_0 + B$.

3. Some particular behaviors are observed. For the PVC geomembrane that includes an internal reinforcement and for the one that has a bonded geotextile, the resistance at the first peak of tensile strength, corresponding to the rupture of the internal reinforcement or the bonded geotextile, and is not sensitive to the test speed. On the other hand, the polymeric part of these two PVC geomembranes, the rupture of which occurs in a second stage at greater deformation, presents a behavior sensitive to the test speed. For EPDM geomembrane, tensile strength is only sensitive to test speed after the 200% elongation level. The ultimate tensile strength of the FPO is less sensitive to the test speed. For the bituminous geomembrane, at a very low test speed, the bitumen creeps by compression in the jaws of the tensile machine and it is no longer possible to measure its tensile strength.

4. It was observed that for the test speed of 100 and 500 mm/min, the geomembrane specimens showed significant internal heating, but for the tested lower test speeds, the internal heating was not significant. Apart from this, a significant change in the tensile behavior was observed. Thus, in the tested test speed range of 0.01 mm/min to 10 mm/min, it seems that only the viscous component of the geomembrane is responsible for the increase in tensile strength with increasing
rate. Beyond the test speed of 10 mm/min, there is a doubling effect related to the internal heating of the tested geomembrane specimens: the viscous component of the geomembranes induces an increase in tensile strength, but this effect is partly counterbalanced by the increase in internal temperature that reduces the internal viscosity of the geomembranes. From the test speed of 10 mm/min and onwards, the increase in the internal temperature 'ΔT' of the specimens just before rupture as a function of the test speed (i.e. test speed) 'v' can be interpreted according to a logarithmic law of the form: ΔT = C log v/v₀ + D.

5. In practical terms, it can be concluded that the geomembrane tensile test standards (see **Table 1**) which mostly standardize test speed of 100 mm/min are ultimately only suitable for the production control of geomembranes, since the only objective is to verify by rapid tests the homogeneity of the geomembranes during their production process. On the other hand, for the design of geomembranes in civil engineering works and structures, in which the actual deformation rates are much lower than the standardized ones, the geomembrane tensile test standards (see **Table 1**) are not safe, because they lead to over-estimated traction resistance values. It is therefore recommended that geomembranes design engineers rely on tensile strength tests performed at very lower test speeds. The lowest test speed used in this study is 0.01 mm/min, but lower test speeds remain a prospect for this study.

6. Finally, in the case where it is necessary to know the resistance of the geomembrane as a function of the temperature, for example, in the case of an installation of this geomembrane in a particularly cold or hot environment, it is once again recommended to carry out tensile tests in a thermal chamber at controlled ambient temperature at test speed lesser than or equal to 10 mm/min, because higher test speeds lead to internal heating of the tested specimen, that modifies the behavior of the material.
# 6 Acknowledgments

This work is part of a PhD thesis carried out at the geosynthetics lab in the National Research Institute for Agriculture, Food and the Environment (INRAE), Aix-en-Provence, France. This thesis is carried out in the context of the project 'BECCA', financed by the European Union under the INTERREG ALCOTRA program.

Thus, the writers are extremely grateful to them for the opportunity to conduct this thesis and for providing the necessary funding. The writers are also grateful to Julien AUBRIET, Alexis DOGHMANE and Nesrin AKEL for their assistance in conducting the experimental tests.

For the purpose of Open Access, a CC-BY public copyright license has been applied by the authors to the present document and will be applied to all subsequent versions up to the Author Accepted Manuscript arising from this submission.

# References

Akel, N., Stoltz, G., Wautier, A., Nicot, F., Touze, N., 2025. Rate-dependent tensile response of Polyvinyl Chloride geomembranes. Geotext. Geomembr. 53, 445-456.
https://doi.org/10.1016/j.geotexmem.2024.11.004

Akpinar, M.V., Benson, C.H., 2005. Effect of temperature on shear strength of two geomembrane-geotextile interfaces. Geotext. Geomembr. 23, 443-453.
https://doi.org/10.1016/j.geotexmem.2005.02.004

ASTM D4885 - 01 (Reapproved 2023), 2023. , in: Standard Test Method for Determining Performance Strength of Geomembranes by the Wide Strip Tensile Method. ASTM International.

ASTM D5617 - 04 (Reapproved 2015), 2015, in: Standard Test Method for Multi-Axial Tension Test for Geosynthetics. ASTM International.
ASTM D6693/D6693M – 20, 2020. , in: Standard Test Method for Determining Tensile Properties of Nonreinforced Polyethylene and Nonreinforced Flexible Polypropylene Geomembranes. ASTM International.

ASTM D7003/D7003M – 03 (Reapproved 2021), 2021. , in: Standard Test Method for Strip Tensile Properties of Reinforced Geomembranes. ASTM International.

ASTM D7275 – 07 (Reapproved 2012), 2012. , in: Standard Test Method for Tensile Properties of Bituminous Geomembranes (BGM). ASTM Standards.

Barentsen, W.M., Heikens, D., 1973. Mechanical properties of polystyrene/low density polyethylene blends. Polymer 14, 579–583. https://doi.org/10.1016/0032-3861(73)90143-2

Bax, B., Müssig, J., 2008. Impact and tensile properties of PLA/Cordenka and PLA/flax composites. Compos. Sci. Technol. 68, 1601–1607. https://doi.org/10.1016/j.compscitech.2008.01.004

Boyce, M.C., Arruda, E.M., Jayachandran, R., 1994. The large strain compression, tension, and simple shear of polycarbonate. Polym. Eng. Sci. 34, 716–725. https://doi.org/10.1002/pen.760340904

Cazzuffi, D., Giroud, J., Scuero, A., Vaschetti, G., 2010. Geosynthetic barriers systems for dams. 9th Int. Conf. Geosynth. - Geosynth. Adv. Solut. Challenging World ICG 2010 115–164.

Chen, K., Kang, G., Lu, F., Chen, J., Jiang, H., 2016. Effect of relative humidity on uniaxial cyclic softening/hardening and intrinsic heat generation of polyamide-6 polymer. Polym. Test. 56, 19–28. https://doi.org/10.1016/j.polymertesting.2016.09.020

Chen, W., Lu, F., Cheng, M., 2002. Tension and compression tests of two polymers under quasi-static and dynamic loading. Polym. Test. 21, 113–121. https://doi.org/10.1016/S0142-9418(01)00055-1

Giroud, J. p., 1995. Evaluation of PVC Geomembrane Shrinkage Due to Plasticizer Loss. Geosynth. Int. 2, 1099–1113. https://doi.org/10.1680/gein.2.0047

Giroud, J.P., 1994. Mathematical Model of Geomembrane Stress-Strain Curves with a Yield Peak 13, 1–22.
Haward, R.N., 1994. Heating effects in the deformation of thermoplastics. Thermochim. Acta 247, 87–109.
https://doi.org/10.1016/0040-6031(94)80115-0

Hine, P.J., Duckett, R.A., Kaddour, A.S., Hinton, M.J., Wells, G.M., 2005. The effect of hydrostatic pressure on the mechanical properties of glass fibre/epoxy unidirectional composites. Compos. Part Appl. Sci. Manuf., 7th International Conference on the Deformation and Fracture of Composites (DFC-7) 36, 279–289. https://doi.org/10.1016/j.compositesa.2004.06.004

Hsuan, G., Schroeder, H., Rowe, R., Mller, W., Greenwood, J., Cazzuffi, D., Koerner, R., 2008. Long-term performace and lifetime prediction of geosynthetics. EuroGeo4 1–40.

Jabbari-Farouji, S., Rottler, J., Lame, O., Makke, A., Perez, M., Barrat, J.-L., 2015. Plastic Deformation Mechanisms of Semicrystalline and Amorphous Polymers. ACS Macro Lett. 4, 147–150.
https://doi.org/10.1021/mz500754b

Jordan, B., Gorji, M.B., Mohr, D., 2020. Neural network model describing the temperature- and rate-dependent stress-strain response of polypropylene. Int. J. Plast. 135, 102811.
https://doi.org/10.1016/j.ijplas.2020.102811

Kennedy, M.A., Peacock, A.J., Mandelkern, L., 1994. Tensile Properties of Crystalline Polymers: Linear Polyethylene. Macromolecules 27, 5297–5310. https://doi.org/10.1021/ma00097a009

Krairi, A., Doghri, I., 2014. A thermodynamically-based constitutive model for thermoplastic polymers coupling viscoelasticity, viscoplasticity and ductile damage. Int. J. Plast. 60, 163–181.
https://doi.org/10.1016/j.ijplas.2014.04.010

Lamri, A., Shirinbayan, M., Pereira, M., Truffault, L., Fitoussi, J., Lamouri, S., Bakir, F., Tcharkhtchi, A., 2020. Effects of strain rate and temperature on the mechanical behavior of high-density polyethylene. J. Appl. Polym. Sci. 137, 48778. https://doi.org/10.1002/app.48778

Lin, P., Liu, J., Wang, S.-Q., 2016. Delineating nature of stress responses during ductile uniaxial extension of polycarbonate glass. Polymer 89, 143–153. https://doi.org/10.1016/j.polymer.2016.02.051
Maurel-Pantel, A., Baquet, E., Bikard, J., Bouvard, J.L., Billon, N., 2015. A thermo-mechanical large deformation constitutive model for polymers based on material network description: Application to a semi-crystalline polyamide 66. Int. J. Plast. 67, 102–126.
https://doi.org/10.1016/j.ijplas.2014.10.004

Merry, S.M., Bray, J.D., 1997. Time-Dependent Mechanical Response of HDPE Geomembranes. J. Geotech. Geoenvironmental Eng. 123, 57–65. https://doi.org/10.1061/(ASCE)1090-0241(1997)123:1(57)

Mullins, L., 1948. Effect of Stretching on the Properties of Rubber. Rubber Chem. Technol. 21, 281–300.
https://doi.org/10.5254/1.3546914

NF EN 14151, 2010., in: Geosynthetics - Determination of burst strength. AFNOR.

NF EN 12311-1, 1999., in: Flexible Sheets for Waterproofing - Part 1: Bitumen Sheets for Roof Waterproofing - Determination of Tensile Properties. AFNOR.

NF EN 12311-2, 2013., in: Flexible Sheets for Waterproofing - Determination of Tensile Properties - Part 2: Plastic and Rubber Sheets for Roof Waterproofing. AFNOR.

NF EN 17323, 2020., in: Geosynthetics – Determination of Tensile Properties of Polymeric Geosynthetic Barriers. AFNOR.

Nielsen, L.E., 1969. Cross-Linking–Effect on Physical Properties of Polymers. J. Macromol. Sci. Part C 3, 69–103. https://doi.org/10.1080/15583726908545897

Noval, A.M., 2015a. Estudio del comportamiento de tres geomembranas de EPDM, PVC-P y PEAD a lo largo del tiempo (Tesis doctoral). Universidad Carlos III, Madrid, Spain.

Ovalle Rodas, C., Zaïri, F., Naït-Abdelaziz, M., 2014. A finite strain thermo-viscoelastic constitutive model to describe the self-heating in elastomeric materials during low-cycle fatigue. J. Mech. Phys. Solids 64, 396–410. https://doi.org/10.1016/j.jmps.2013.10.010
Rowe, R.K., Rimal, S., Sangam, H., 2009. Ageing of HDPE geomembrane exposed to air, water and leachate at different temperatures. Geotext. Geomembr. 27, 137-151.
https://doi.org/10.1016/j.geotexmem.2008.09.007

Shen, F., Kang, G., Lam, Y.C., Liu, Y., Zhou, K., 2019a. Thermo-elastic-viscoplastic-damage model for self-heating and mechanical behavior of thermoplastic polymers. Int. J. Plast. 121, 227-243.
http://dx.doi.org/10.1016/j.ijplas.2019.06.003

Shen, F., Kang, G., Lam, Y.C., Liu, Y., Zhou, K., 2019b. Thermo-elastic-viscoplastic-damage model for self-heating and mechanical behavior of thermoplastic polymers. Int. J. Plast. 121, 227-243.
https://doi.org/10.1016/j.ijplas.2019.06.003

Srivastava, V., Chester, S.A., Ames, N.M., Anand, L., 2010. A thermo-mechanically-coupled large-deformation theory for amorphous polymers in a temperature range which spans their glass transition. Int. J. Plast., Special Issue In Honor of Lallit Anand 26, 1138-1182.
https://doi.org/10.1016/j.ijplas.2010.01.004

Wesseloo, J., Visser, A.T., Rust, E., 2004. A mathematical model for the strain-rate dependent stress-strain response of HDPE geomembranes. Geotext. Geomembr. 22, 273-295.
https://doi.org/10.1016/j.geotexmem.2004.02.002

Zanzinger, H., Engelsing, K., Gerets, B., 2023. Strain hardening behavior of HDPE geomembranes. E3S Web Conf. 368, 02009. https://doi.org/10.1051/e3sconf/202336802009

Zhang, X., Ma, Z., Wu, Y., Liu, J., 2021. Response of Mechanical Properties of Polyvinyl Chloride Geomembrane to Ambient Temperature in Axial Tension. Appl. Sci. 11, 10864.
https://doi.org/10.3390/app112210864

Zhang Y., Yan Z., 1993. THE GENERAL THEORY OF VISCOELASTICITY UNDER NONCONSTANT TEMPERATURE STATES. Chin. J. Theor. Appl. Mech. 25, 685-696. https://doi.org/10.6052/0459-1879-1993-6-1995-694