Process Induced Residual Stress in Thermoset Polymer with Metallic Insert

Jørgensen, Jens Grandjean

4. term

Design of Mechanical Systems, Master

2014

2014-06-02

85 pages

In this project, process induced stress and strain in a simple epoxy test specimen, with a steel insert, is considered. The subject is studied by both experimental and numerically methods. Through experimental in-situ measurements, using digital image correlation (DIC), the average strain is obtained, and afterwards separated into a thermal and a chemical contribution. The residual stress of the test specimen is evaluated by using photoelasticity. However, the stress-optical law is not valid for this problem, because the temperature varies over time. Hence, another approach is considered, where the change in the photoelastic measurement is considered, when the insert is removed. This is considered to yield good results of the residual stress at the end of the process. The test specimen is furthermore considered theoretically through a numerical model. The model is based on the finite element method (FEM), and has been coded in MATLAB. It includes the chemical curing process and material properties, which is dependent on degree of cure and temperature. Different material models have been implemented in the numerical model, based on elastic, viscoelastic, or pseudo-viscoelastic considerations. The numerical model yields strain results which correlate very well with the average strain, obtained by the DIC measurements. By using the pseudo-viscoelastic model, known as the cure hardening instantaneously linearly elastic (CHILE) model, reasonable correlation with the photoelastic stress measurements is obtained.

Process inducerede egenspændinger ; Hærdeplast ; Epoxy ; Ulineær viscoelastisk FEM

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