Polycarbonate is an amorphous polymer which exhibits a pronounced strength-differential effect between compression and tension. Also strain rate and temperature influence the mechanical response of the polycarbonate. The concept of stress mode dependent weighting functions is used in the proposed model to simulate the asymmetric effects for different loading speeds. In this concept, an additive decomposition of the flow rule is assumed into a sum of weighted stress mode related quantities. The characterization of the stress modes is obtained in the octahedral plane of the deviatoric stress space in terms of the mode angle, such that stress mode dependent scalar weighting functions can be constructed. The resulting evolution equations are updated using a backward Euler scheme and the algorithmic tangent operator is derived for the finite element equilibrium iteration. The numerical implementation of the resulting set of constitutive equations is used in a finite element program for parameter identification. The proposed model is verified by showing a good agreement with the experimental data. After that the model is used to simulate the laser transmission welding process.

a b s t r a c tGlassy polymers such as polycarbonate exhibit different behaviours in different loading scenarios, such as tension and compression. To this end a flow rule is postulated within a thermodynamic consistent framework in a mixed variant formulation and decomposed into a sum of weighted stress mode related quantities. The different stress modes are chosen such that they are accessible to individual examination in the laboratory, where tension and compression are typical examples. The characterisation of the stress modes is obtained in the octahedral plane of the deviatoric stress space in terms of the Lode angle, such that stress mode dependent scalar weighting functions can be constructed. Furthermore the numerical implementation of the constitutive equations into a finite element program is briefly described. In a numerical example, the model is used to simulate the laser transmission welding process.

This article presents the influence of the process parameters in laser transmission welding for plastics on the residual stress in the welded part. The contour welding process is modeled by means of finite element (FE) simulation. In this process, the weld seam is only partially heated, i.e., only part of it melts. The calculations are performed using a material model that describes the time-dependent temperature and stress development in a plate geometry, making allowance for the material's asymmetric compressive-tensile behavior. Experimental data were measured under different load cases to present the time-dependent material behavior, and then implemented in numerical terms by formulating the necessary constitutive equations. The calculations to simulate the influence of process parameters on the residual stress behavior were performed using a finite element model that was developed. The simulation covers the entire welding process, including the heating and cooling stages.

No abstract

No abstract