Process-Induced Residual Stress Analysis by Resin Transfer Molding

Abstract

The objective of this study is to investigate the residual stress development during the resin transfer molding process. The analysis was based on the strain measurement tests during the entire cure process of unidirectional carbon fiber–epoxy matrix composite laminate using aluminum mold. The investigation efforts were particularly focused on the verification of the strain development mechanism. Although complex interference between the mold structure and the composite laminate was observed during the process, it was found that the final residual strain of the laminate was induced only by thermal mismatch during the cooldown stage. Based on the observation, the residual stresses were calculated by a viscoelastic classical laminated plate theory. The viscoelastic modulus in the calculations was obtained by a series of stress relaxation tests of the material. The curvatures of [0°/90°] asymmetric laminate were calculated, and the results were compared with the experimental data. The results showed that the residual stress developed by the resin transfer molding could be calculated by considering only the cooldown stage of the process.

A Review on the Mechanical Modeling of Composite Manufacturing Processes

“…There are two different forms of viscoelastic models: differential and integral form. Generally, the integral form has been used in literature by several researchers [ 64 , 95 – 103 ]. where and is the current reduced time, is the past reduced time, t is the current time, is the past time, is the temperature ( T ) and degree of cure or crystallization ( ) dependent shift factor.…”

“…In the manufacturing of complex shaped composite parts, the RTM is one of the widely used techniques which involves transfer of resin into a closed mold containing previously laid up dry reinforcement preforms. RTM simulations have been carried out in many studies to predict residual stress and deformations [ 37 , 59 , 66 , 67 , 95 , 148 – 151 ]. Process models were generally divided into sub-models including heat transfer and cure kinetics, flow and compaction and stress development [ 37 , 59 , 66 , 67 , 149 ].…”

“…The residual stress development was captured in [ 95 ] by implementing a viscoelastic model using the classical laminate theory (CLT). The thermal mismatch during the cooldown stage was found to be the dominant effect for the residual stress build up since the aluminum mold applied a strong constraint effect on the strain built up.…”

A comparison of process-induced residual stresses and distortions in composite structures with different constitutive laws

“…35 Some fundamental characteristics for some resin are investigated recently taking into account CTEs of materials, cure chemical shrinkage, and stress relaxation. 9,11,17,33,[36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] Substantial investigations on viscoelastic behaviors of composite structures have been presented to predict process-induced residual stresses and distortions in composite structures. 8,16,[54][55][56][57][58][59] The comparatively significant studies are presented by Zocher et al, 58 Kim and White, 60,61 Adolf and Martin, 41 Simon et al, 62 Prasatya et al, 44 Ruiz and Trochu, 31 and Zobeiry.. 34 Zocher et al proposed a three-dimensional finite element formulation for thermo-viscoelastic orthotropic media using integral form.…”

Investigation of cure stresses in non-conductive adhesive interconnects

“…Cure-induced stresses are very common and ubiquitous in such applications. Polymerization shrinkage in dental materials is a critical issue and the contraction stress that occurs during the curing process could cause the debonding and lead to clinical failures [118,119]. One of the significant problems in composite laminates is the development of process-induced stresses which lead to warpage of composite structures and could initiate the failure of the laminates [120][121][122].…”