Proceedings of the 10th World Congress on Mechanical, Chemical, and Material Engineering (MCM'21)
Prague, Czech Republic Virtual Conference – August, 2021
Paper No. ICMIE 102
DOI: 10.11159/icmie21.102

Experimental Investigation into Quasi-Static Crushing of CFRP
Composite Cylindrical Tubes after Thermal Aging
Tamer A. Sebaey

Engineering Management Department, College of Engineering,
Prince Sultan University, Riyadh, Saudi Arabia
Mechanical Design and Production Department, Faculty of Engineering,
Zagazig University, Zagazig, Sharkia, Egypt
sepaey@hotmail.com & tsebaey@psu.edu.sa
Abstract - For the effective design of polymeric composites, designers need not only to make sure that they meet specific mechanicalproperty criteria but also to consider the impact of environmental factors, which limit the development of safe and economical designs.
As one of the expected environmental factors during the composite service life, thermal aging is addressed in the current paper forcomposite tubes subjected to crushing loading. In the present experimental study, tubes of carbon/epoxy composites were subjected tothermal aging at 90ºC, 120 ºC, 150 ºC, and 180 ºC before being subjected to quasi-static crushing. Besides, non-aged specimens were
tested for comparison. The results showed that thermal aging has no effects on the load-displacement profile and crushing mode. On theother hand, the crashworthiness, assessed by the peak load, the energy absorbed and the specific energy absorbed, decreased by increasing
the aging temperature to 120 ºC, due to thermal fatigue of the matrix and the fiber/matrix interface. At 150 ºC (the closest value to the
𝑇𝑇𝑔𝑔 ), the crashworthiness improved as a result of the post-curing process. After that temperature, the crashworthiness parameters reduced
as a result of chain rupture and matrix oxidation. Based on these results, the designer needs to consider 10-15% margins in the energy
absorption of carbon fiber-reinforced plastic (CFRP) composites to compensate for the thermal aging effect.
Keywords: Thermal Aging; CFRP composites; Crushing; Energy Absorption

1. Introduction

Nowadays, Fiber Reinforced Polymers (FRPs) are used to produce parts of aircraft, marine, and automotive structures
to reduce overall weight, with adequate strength and stiffness, and reduce CO2 emission as well as improving the fuelefficiency [1]. Energy absorbers are used in automotive mainly to absorb the collision energy in a controlled manner in
accidents before transferring it to the passenger compartment, which increases passenger safety. Traditionally, metallic
structures have been extensively considered as energy absorbers because of their significant plastic deformation
characteristics and capabilities in processing. Nowadays, composites are being used widely in these structures due to its
ability to consume the impact energy in different damage mechanisms [2].
Several factors affect the crushing response of FRP composite tubes. These factors include the fiber orientation, the tube
geometry, the fiber and matrix material, the crushing speed, the triggering mechanism, the filler, and the impactors' geometry[3]. When exposed to environmental effects, various physical, and chemical reactions may occur in FRP composites, causing
degradation of their mechanical, physical and chemical properties [4]. The viscoelasticity of the matrix material substantiallyinfluences the temperature dependence of polymeric composites. When the ambient temperature is near/above the glasstransition temperature 𝑇𝑇𝑔𝑔 , the resin matrix softens, transitioning from a glass-like material into a rubber-like material [5]. In
this case, the resin matrix cannot provide sufficient stress transfer between the fibers and the matrix, resulting in reduced
matrix stiffness and a degraded fiber-matrix interface [6]. In the literature, several authors studied the effect of thermal aging
on tensile [6], compression [7], bending [8], and impact [9] properties of FRP composites. To the authors best of knowledge,
data available on the crushing after thermal aging of FRP composites is very limited [10]. The aim is to study the effect ofthermal aging on the crushing characteristics (both crushing and post-crushing stages) of the CFRP composite tube by thequasi-static axial compression test.

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2. Material and Test Specimen

Roll wrapped unidirectional tubes, manufactured by DragonPlateTM, are used in the current analysis. This highstrength to weight carbon fiber tubing is fabricated from unidirectional carbon fiber. The layers are oriented to provide
high bending stiffness and axial strength and high hoop strength (resistance to crushing from a side load). The composite
tube is made of carbon fiber of 2.3 x 105 MPa elastic modulus and 4800 MPa ultimate strength with a matrix glasstransition temperature of 𝑇𝑇𝑔𝑔 = 160 ºC. The tubes were delivered as one beam of 1200 mm length, 25.4 mm inner diameter,and 1.143 mm wall thickness. Each tube was sliced into the desired specimens' height of 60 mm using a computercontrolled abrasive cutting machine.
Parts of the tubes were cut and used to estimate the fiber volume fraction. The cut samples were measured (massand volume) and subjected to ignition, as per the ASTM D3171. After ignition, the fibers remained in the container,
where its mass was used to estimate the fiber volume fraction. Five samples were measured using the current
methodology, and the result was that the fiber volume fraction 𝜐𝜐𝑓𝑓 = 54.1% with a standard deviation of 2.6%.

3. Thermal Aging

The effect of temperature aging on the crushing behavior of composite tubes was studied using an insulated
temperature-controlled air oven (JS0F-150) to provide high-temperature environments. Specimens were subjected to a
constant temperature for six hours, the constant aging time used for the current study. The aging temperature values
were 23 ºC (RT), 90 ºC, 120 ºC, 150 ºC, and 180 ºC. It is well-established that the aging temperature effect is highly
dependent on the value of the 𝑇𝑇𝑔𝑔 [11]. Consequently, the values of the temperatures were selected to have most of thereadings before the 𝑇𝑇𝑔𝑔 and one reading after the Tg. During its working conditions, composites are usually subjected totemperatures that are mostly below the 𝑇𝑇𝑔𝑔 . However, in some cases, during its service time, composites can be subjected
to temperatures higher than its glass-transition temperature [12]. The mass values of the specimens were measured before
and after the thermal exposure, and the values are recorded in Table 1. The values listed in Table 1 are the average per
three samples tested at each temperature. The differences in the mass with the different temperature shows an
insignificant effect, which can be justified with the short aging time, compared to the data available in the literature [13].
Table 1: Average mass of the CFRP composite tubes before and after the thermal aging.

Temperature
(ºC)

90
120
150
180

Mass before
(g)
8.77
9.03
8.14
8.08

Mass after
(g)
8.73
8.99
8.11
8.05

4. Quasi-Static Crushing Tests

Difference in mass
Percentage
Standard deviation
0.4
0.08
0.37
0.05
0.37
0.01
0.37
0.12

Quasi-static crushing tests were performed to assess the crushing capabilities of the composite tubes after thermal
aging. The tests were conducted using an Instron 8500 digital testing machine with a full-scale load range of 250 kN.
Two steel platens were set parallel to each other before starting the test, and the behavior of each specimen undercompression was monitored and recorded. The acquisition system of the universal testing machine recorded the loaddisplacement data at a constant cross-head speed of 5 mm/min [14]. Three samples were tested for each condition andgood agreement between their results were obtained.
The load-displacement data and profile were used to assess the energy absorption [15]. Peak load 𝑃𝑃𝑖𝑖 is usuallyindicated highest point before the post-crushing zone. The mean load 𝑃𝑃𝑚𝑚 is the average load during the post crushingstage. The collapsible energy absorption devices must also provide a long deformation path to sufficiently and gradually
reduce the deceleration of the protected occupants. Therefore, when evaluating the crashworthiness of an energy
absorption device, great attention should be directed to its instantaneous crush force efficiency 𝐶𝐶𝐶𝐶𝐶𝐶, which is definedas the ratio between 𝑃𝑃𝑚𝑚 and 𝑃𝑃𝑖𝑖 . The energy absorbed 𝐸𝐸 is the force value at each compression distance, which it evaluates
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the area under load-displacement, and is defined as 𝐸𝐸 = ∫ 𝑃𝑃 𝑑𝑑𝑑𝑑. Finally, to access the amount of energy consumed by each
unit mass, the specific energy absorbed (𝐸𝐸𝑆𝑆 ) is used. Details on each parameter can be found in [10].

5. Results and Discussions

5.1. Load-displacement and crushing mechanism
The direct output of the machine is the load-displacement profile. As samples, the data obtained for the specimens atroom temperature and at 120 ºC is shown in Figure 1. Good repeatability is shown in Figure 1, for the same condition. It is
worth remarking that the same behavior is shown for the other three test conditions.

(a)

(b)

Fig.1: Load-displacement profile of the specimens (a) without thermal aging and (b) with thermal aging at 120 ºC. Three samples areshown for each condition.

The load-displacement profiles in Figure 1 are typical for composite tube subjected to axial crushing, see for example
the results in [16]. The first stage is the pre-crushing stage. During this stage, the load-displacement relationship is linear, as
it is clear in Figure 1. No visible damage is associated with this pre-crushing stage, Figure 2(i). The end of the first stage isthe peak load, after which a drop in the load-carrying capacity of the specimen is recognized. After the peak load, the postcrushing stage starts. On the load-displacement profile, this stage is characterized by several peaks and valleys, with a small
amplitude, which indicates a steady-state crushing. On the specimen, Figure 2(ii-vi), this stage is characterized by tearing,fragment, and folding damage. Several authors [17,18] studied the fractography during the post-crushing stage. They
concluded that most of the known damage mechanisms (matrix cracking, fiber-matrix debonding, fiber micro buckling,delaminations, and fiber failure) are contributing to the composite tube behavior. This stage continues until the specimen's
final densification (at which the specimen is not able to carry any extra load and the stiffness of the machine starts tocontribute to the load-displacement profile). The images of the damage propagation and initiation do not show any
dependency of the aging temperature. The image of the specimen after crushing shows that the outer layer (0º) experiences
longitudinal splitting driven by matrix cracking, and then it is folded outside, Figure 2(vii). The other layers are crushinginward to fill in the internal hole of the tube.
5.2. Crashworthiness Assessment
Figure 3 shows the effect of the aging temperature on the load-displacement profile of the CFRP composite tubes. The
data is considered for a maximum displacement of 50 mm, for ease comparing the energy absorbed at different temperatures.
The load-displacement profile shown in Figure 3 is the mean of three specimens assessed by each condition. The data showsthat the highest load-carrying capacity is recorded at RT, as well as at 150 ºC. During the post crushing stage, profiles arevery similar. In more detail, the peak force 𝑃𝑃𝑖𝑖 and the average crushing force 𝑃𝑃𝑚𝑚 are shown in Figure 4. The highest peak

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load is recorded at RT, which decreases by increasing the aging temperature up to 120 ºC. At 150 ºC, an increase in thepeak load is recorded; another decrease follows that. Three different phenomena govern this fluctuation in the loadcarrying capacity.

Fig. 2: Crushing mechanism of the CFRP composite tube.

For aging with temperatures much lower than 𝑇𝑇𝑔𝑔 , thermal fatigue due to the mismatch of the thermal expansion
coefficient between the carbon fibers and the epoxy matrix participates to the material degradation [19], which is the
responsible of the first degradation in the 𝑃𝑃𝑖𝑖 between RT and 120 ºC. For aging temperatures close but lower than 𝑇𝑇𝑔𝑔 , theconsolidation phase occurs due to the post-curing reaction that facilitates the adhesion between the fibers and the matrix,
maintaining and improving the load-carrying capacity of the composite tube. Similar results were already reported by
Garcia-Moreno [20] under impact and bending and by Shaoquan et al. [21] under impact loading. At aging temperatures
above 𝑇𝑇𝑔𝑔 , chemical aging mechanisms, which involve chain rupture, oxidation, and catalytic reaction of gases andpyrolization, occurred [5], which is the responsible of the second degradation in the peak load after 150 ºC.
On the other hand, the aging temperature does not show any impact on the average crushing load (the values shownin Figure 4 are the average of three samples). As a result, the crush force efficiency (CFE) increases by decreasing thepeak load and vice versa, Table 2. Although it is improving by temperature up to 120 ºC, the 𝐶𝐶𝐶𝐶𝐶𝐶 of the tubes underinvestigation is still low, compared to the optimal value of 100%. A woven layer on the surface and/or a filler may
improve such a parameter, which is beyond the scope of the current study. Similar to the load-carrying capacity, theenergy absorbed, Figure 5, and the specific energy absorbed, Table 2, are affected by the chemical changes during thethermal aging. The energy absorbed at room temperature is the highest recorded, which is followed by a reduction in
the energy absorbed, up to 120 ºC. At 150 ºC, the energy absorbed increases due to the post-curing reaction before being
decreased after the 𝑇𝑇𝑔𝑔 . The reduction in the energy absorbed due to the thermal aging from RT to 120 ºC is 10%. On thenormalized values (𝐸𝐸𝑆𝑆 ), Table 2, the maximum reduction is 13.6%. Due to the post-curing process at 150 ºC, thesecomposite tubes recover most of its original energy per unit mass (𝐸𝐸𝑆𝑆 ).
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Fig. 3: Summary of the effect of the aging temperature on the load-displacement profile of the CFRP composite tubes.

Fig. 4: Peak and average crushing force as functions of the aging temperature.
Table 2: Crush force efficiency CFE and the specific energy absorbed Es of the test campaign at different aging temperature. (CoV isthe coefficient of variation of the measurements at each aging temperature)

Temperature
(ºC)

23
90
120
150
180

Crush force efficiency
𝐶𝐶𝐶𝐶𝐶𝐶 (%)
𝐶𝐶𝐶𝐶𝐶𝐶 (%)
52.6
10.1
57.1
8.14
62.8
3.74
58.6
8.31
61.5
14.1

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Specific energy
𝐶𝐶𝐶𝐶𝐶𝐶 (%)
𝐸𝐸𝑆𝑆
80.7
8.34
72.2
8.83
69.7
15.9
50.5
1.34
78.4
4.40

Fig. 5: Energy absorbed 𝐸𝐸 as functions of the aging temperature

In real structure applications, composite tubes can be exposed to air at -73 ºC to 80 ºC in aerospace whereas, it is
exposed to -140 ºC to 120 ºC in space applications [22]. In automotive, the temperature around the engine and exhaustcan exceed the 200 ºC [23]. For light weighting, transportation applications use polymeric fiber-reinforced composites
for their structures, with an extra advantage of its crashworthiness. The results obtained in the current study
recommended that 10-15% design margins need to be considered while designing FRP composites to compensate forthe temperature aging in real working environment.

6. Conclusion

The current paper pretested an experimental study to investigate the effect of thermal aging on the crashworthinessparameters of cylindrical CFRP tubes. The specimens were tested under compression after thermal aging at 90ºC, 120ºC,
150ºC, and 180ºC, in addition to tests at room temperature. The peak and average crushing forces, the crush force
efficiency, the energy absorbed, and the specific energy were used to assess the composite tubes' crashworthiness.
The results did not show any dependency of the load-displacement profile neither the apparent crushing mechanismon the applied thermal aging. On the other hand, the peak force, the energy, and the specific energy showed degradation
by increasing the temperature up to 120 ºC, controlled by the matrix cracking and debonding due to thermal mismatch
between the fiber and matrix and matrix degradation. At 150 ºC, the crashworthiness improved, as a result of the postcuring process of the matrix. At a temperature higher than the 𝑇𝑇𝑔𝑔 (at 180 ºC), the crashworthiness parameters decreased
as a result of the chain rupture, oxidation, and catalytic reaction of the matrix.

Acknowledgements

The author would like to acknowledge the support of Prince Sultan University for covering the conference
attendance of this article. In addition, the financial support of the PSU through the S&M Lab and SEED-PSU-2020-16
is acknowledged.

References[1] F. K. Rajak, D. D. Pagar, R. Kumar, C. I. Pruncu, “Recent progress of reinforcement materials: a comprehensive
overview of composite materials,” J. Mater. Res. Technol., vol. 8, pp. 6354-6374, 2019.
[2] E. Mahdi, T. A. Sebaey, “An experimental investigation into crushing behavior of radially stiffened GFRP composite
tubes,” Thin-Walled Struct., vol. 76, pp. 8-13, 2014.
[3] E. Mahdi, A. M. S. Hamouda, A. S. Mokhtar, D. L. Majid, “Many aspects to improve damage tolerance of collapsible
composite energy absorber devices,” Compos. Struct., vol. 67, pp. 175-187, 2005.

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[4] T. Q. Liu, X. Liu, P. Feng, “A comprehensive review on mechanical properties of pultruded FRP composites subjected
to long-term environmental effects,” Compos. Part B, vol 191, no. 107958, 2020.
[5] M. Leone, S. Matthys, M. A. Aiello, “Effect of elevated service temperature on bond between FRP EBR systems andconcrete. Compos. Part B, vol 40, pp. 85-93, 2009.
[6] E. J. Bosze, A. Alawar, O. Bertschger, Y. I. Tsai, S. R. Nutt, “High-temperature strength and storage modulus in
unidirectional hybrid composites,” Compos. Sci. Technol., vol 66, pp. 1963-1969, 2006.
[7] H. Katoh, T. Ogasawara, S. Sugimoto, T. Ishikawa, “Durability of carbon fiber/epoxy composites under the elevatedtemperatures,” in Proceedings of the 15th Composite Durability Workshop, Kanazawa, JAPAN. 2010.
[8] T. R. Gentry, L.C. Bank, A. Barkatt, L. Prian, “Accelerated test methods to determine the long-term behavior ofcomposite highway structures subject to environmental loading,” J. Compos. Technol. Res., vol. 20, pp. 38-50, 1998.
[9] S. Ma, Y. He, L. Hui, L. Xu, “Effects of hygrothermal and thermal aging on the low-velocity impact properties of carbon
fiber composites,” Adv. Compos. Mater., vol 29, no. 1630054, 2019.
[10] T.A. Sebaey, “Effect of Exposure Temperature on the Crashworthiness of Carbon/Epoxy Composite Rectangular Tubes
Under Quasi-Static Compression,” Polymers, vol. 12, no. 2028, 2020.
[11] G. M. Odegard, A. Bandyopadhyay, “Physical aging of epoxy polymers and their composites,” J. Polym. Sci. Part B,
vol. 49, pp. 1695-1716, 2011.
[12] C. Soutis, “Fibre reinforced composites in aircraft construction,” Prog. Aeosp. Sci., vol. 41, pp. 143-151, 2005.
[13] P. Alam, C. Robert, C. M. Bradaigh, “ Tidal turbine blade composites - A review on the effects of hygrothermal aging
on the properties of CFRP,” Compos. Part B, vol. 149, pp. 248-259, 2018.
[14] T. A. Sebaey, E. Mahdi, “Crushing behavior of a unit cell of CFRP lattice core for sandwich structures application,”Thin-Walled Struct. vol. 116, pp. 91-95, 2017.
[15] T. A. Sebaey, E. Mahdi, A. Shamseldin, E. O. Eltai, “ Crushing behavior of hybrid hexagonal/octagonal cellularcomposite system: All made of carbon fiber reinforced epoxy,” Mater. Des., vol. 60, pp. 556-562, 2014.
[16] E. Mahdi, A. M. H. Hamouda, T. A. Sebaey, “ The effect of fiber orientation on the energy absorption capability ofaxially crushed composite tubes,” Mater. Des., vol. 56, pp. 923-928, 2014.
[17] R. D. Hussein, D. Ruan, G. Lu, I. Sbarski, “Axial crushing behaviour of honeycomb filled square carbon fibre reinforced
plastic (CFRP) tubes,” Compos. Struct., vol. 144, pp. 166-179, 2016.
[18] Y. Wang, J. Feng, J. Wu, D. Hu, “Effects of fiber orientation and wall thickness on energy absorption characteristics ofcarbon-reinforced composite tubes under different loading conditions. Compos. Struct., vol.153, pp. 356-368, 2016.
[19] L. Olivier, C. Baudet, D. Bertheau, “ Development of experimental, theoretical and numerical tools for studying thermo
oxidation of CFRP composites,” Compos. Part B, vol. 40, pp. 1008-1016, 2009.
[20] I. Garcia-Moreno, M. A. Caminero, G. P. Rodriguez, J. J. Lopez-Cela, “Effect of thermal ageing on the impact damage
resistance and tolerance of carbon-fibre-reinforced epoxy laminates,” Polymers, vol 11, no. 160, 2019.
[21] W. Shaoquan, D. Shangli, G. Yu, S. Yungang, S, “Thermal ageing effects on mechanical properties and barely visible
impact damage behavior of a carbon fiber reinforced bismaleimide composite,” Mater. Des., vol 115, pp. 213-223, 2017.
[22] E. Ernault, E. Richaud, B. Fayolle, “Origin of epoxies embrittlement during oxidative ageing,” Polym. Test., vol. 63,
pp. 448-454, 2017.
[23] P. Merati, C. Davis, K. H. Chen, J. P. Johnson, “Underhood buoyancy driven flow-an experimental study,” J. Heat
Transfer, vol. 133, no. 082502, 2011.

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