Thermoformed glass fiber reinforced polypropylene: Microstructure, mechanical properties and residual stresses

Abstract

The objective of this work was to characterize the microstructure, mechanical properties and residual stresses in glass fiber reinforced polypropylene (PP) composites with respect to the thermoforming parameters and as a function of the fiber‐matrix interface quality. First, differential scanning calorimetry (DSC) was used to investigate the crystallization behavior of the PP matrix. Second, short beam shear tests and tensile tests in the ±45° directions have been conducted to characterize respectively the interfacial strength and the matrix properties in the composites. Finally, residual stresses were measured via the curvatures of unsymmetric cross‐plied laminates. The cooling rate was found to be a critical parameter of the molding process since the matrix crystallization temperature, the interfacial strength as well as the residual stresses showed large variations with various cooling rates. At slow cooling, the crystallization process initiates at higher temperatures and covers longer time periods resulting in more spherulitical matrix structures. In this case, the composites becomes stiffer but also fragile indicating a decrease in the stress transfer efficiency at the interface level. This effect was also observed in the improved interface system, suggesting that the fiber‐matrix interaction operates through the amorphous phase surrounding the fibers. The fiber‐matrix interface improvement was accompanied by an increase in residual stresses, possibly due to the inhibition of some stress relief mechanism.

Effects of thermal histories on interfacial properties of carbon fiber/polyamide 6 composites: Thickness, modulus, adhesion and shear strength

“…And these features are, in turn, affected by variations of thermal histories [5] which is here defined as the thermal treatment process polymers experience from their molten temperature to their final service temperature. However, inconsistencies also exist for the influences of cooling rate [1,[6][7][8][9][10] and annealing treatment [1,6,11,12] on IFSS and LTE mainly for the differences of fiber/polymer systems and processing conditions. This implies that a systematic study is required to characterize these parameters and clarify the thermal history effects on them and strength of interface and composites, which is essential for the optimization of the fabrication process from the material design point of view as well as for improving macroscopic mechanical performance from the structural design point of view [13,14].…”

Influence of Cure Regime on the Strain Development in an Epoxy Resin as Monitored by a Fiber Bragg Grating Sensor

“…Due to warpage of a non-symmetrical structure of laminates based on the classical laminate theory conclusions can be drawn from the induced stresses. [30,31] Further techniques to determine residual stresses are of destructive character and often based on the stress relaxation behaviour of the material. [32][33][34] The build-up of residual stresses in thermoset films was investigated for resins with different crosslink densities by Lange.…”

Computational and experimental analysis of fusion bonding in thermoplastic composites: Influence of process parameters

“…The manufacturing of semi-crystalline thermoplastic composites in particular requires a well defined thermal process history. (Bureau et al, 2002;Bureau and Denault, 2004;Perrin et al, 2003;Trudel-Boucher et al, 2006;Youssed and Denault, 1998;Plummer et al, 2003;Cho and Kardos, 1995;Ghasemi Nejhad, 1993;Ye et al, 1995;Schultz, 1984). The primary objective of this study is to investigate the influence of the process parameters on the bond strength.…”