INSTITUT

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

# THERMOMECHANICAL COMPREHENSION OF THE BEHAVIOR OF SELF-REINFORCED COMPOSITES AND ITS UHMWPE REINFORCEMENTS

C. Roiron¹,³, E. Lainé¹, J-C. Grandidier¹, N. Garois² and C. Vix-Guterl³

¹ Institut Pprime, UPR3346 CNRS, ISAE-ENSMA, Université de Poitiers, France

² Centre de Recherche Hutchinson, Châlette-sur-Loing, France

³ TotalEnergies S.A., Paris, France

<figure><img src="image_2.png" /></figure>

## CONTEXT

### Major challenge: reducing energy consumption

In the automotive industry, it must be done during:

* manufacturing phase,

* use phase,

* end of life of a vehicle

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

Lightening of
structures

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

Use recycled and
recyclable materials

<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /></figure>

When fibers nature
≠ from matrix
nature

<figure><img src="image_7.png" /></figure>

Potential of self-
reinforced
composites [2]

<figure><img src="image_8.png" /></figure>

Use of composite
materials

On the market, **95%** [1] are **glass fiber** reinforced polymer composites

## THERMOMECHANICAL BEHAVIOR OF UHMWPE YARNS

<figure><img src="image_9.png" /></figure>

Monotonous tensile tests at
different temperatures on yarns [3]

<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /></figure>

<figure><img src="image_12.png" /></figure>

Behavior transition (≈ [47;50]°C)

<figure><img src="image_13.png" /></figure>

DSC of UHMWPE yarns

<figure><img src="image_14.png" /></figure>

Phase transition is influenced by:

* A solicitation

* The stress (holding of yarns)

* Annealing

<figure><img src="image_15.png" /></figure>

Mold for preparing
composite plates

Compression molding process on a
tensile machine

Load-unload tensile tests at
different temperatures on yarns

<figure><img src="image_16.png" /></figure>

Counter-curvatures present,
synonymous of a **hyperelastic**
**type of behavior** (idem at 23°C)

Similar tangent modulus (at
location 2 and 4, idem at 23°C)

<figure><img src="image_17.png" /></figure>

No loops, behavior similar to
elasto-viscoplasticity

Similar tangent modulus (at
location 3 and 4)

Complex behavior for the UHMWPE yarns

<figure><img src="image_18.png" /></figure>

Tensile tests with strain control
thanks to marker tracking

<figure><img src="image_19.png" /></figure>

<figure><img src="image_20.png" /></figure>

## SPECIFIC BEHAVIOR OF SRPE COMPOSITES

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

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

Inflection point present for all conditions
analyzed

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

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

<figure><img src="image_25.png" /></figure>

Yarns are expressed from the beginning

As a consequence of fibers misalignment

**Inflection point** caused by the misalignment of the fibers due to their **compression**, generated during the **cooling** of the plates due to the large **difference in the thermal expansion coefficients** of the components

* ☒ Related to a too fast cooling speed

* ☒ Related to the nature of the matrix

* ☒ Related to a degraded interface

* ☒ Related to the nature of the SRP

* ☑ Related to the intrinsic nature of UHMWPE reinforcements

<figure><img src="image_26.png" /></figure>

SEM observations of the section of
a monofilament SRPE

<figure><img src="image_27.png" /></figure>

Tensile tests performed on SRPA
(Self-Reinforced PolyAmide)

## CONCLUSION

* **Complex behavior** of Doyentrontex® commercial yarns: observation of a behavior transition due to morphology transition under stress and/or temperature

* **Specific** behavior of SRPE for low deformations: appearance of an **inflection point** due to the **large difference between the thermal expansion coefficients** of the yarns and the matrix

* For these promising composites, and even more than for more conventional composites, it is very important to know the behavior of the reinforcements which is complex to improve the understanding and prediction of the thermomechanical behavior

<figure><img src="image_28.png" /></figure>

<figure><img src="image_29.png" /></figure>

<figure><img src="image_30.png" /></figure>

<footnote>[1] E. Witten, V. Mathes, M. Sauer, and M. Kühnel. 2018. « Composites Market Report 2018, Market developments, trends, outlooks and challenges »</footnote>

<footnote>[2] N. J. Capiati and R. S. Porter, 1975. « The Concept of One Polymer Composites Modelled with High Density Polyethylene ». Journal of Materials Science 10 (10): 1671-77. https://doi.org/10.1007/BF00554928.</footnote>

<footnote>[3] C. Roiron, E. Lainé, J.-C. Grandidier, D. Olivier, N. Garois, and C. Vix. 2020. « Study of the Thermomechanical Behavior of UHMWPE Yarns under Different Loading Paths ». Polymer Testing 89. https://doi.org/10.1016/j.polymertesting.2020.106717.</footnote>

<footnote>[4] L. Govaert, B. Brown, P. Smith. 1992. « Temperature Dependence of the Young's Modulus of Oriented Polyethylene ». Macromolecules 25 (13): 3480-83. https://doi.org/10.1021/ma00039a027.</footnote>