No abstract

Synchrotron Laue microdiffraction and Digital Image Correlation measurements were coupled to track the elastic strain field (or stress field) and the total strain field near a general grain boundary in a bent bicrystal. A 316L stainless steel bicrystal was deformed in situ into the elasto-plastic regime with a four-point bending setup. The test was then simulated using finite elements with a crystal plasticity model comprising internal variables (dislocation densities on discrete slip systems). The predictions of the model have been compared with both the total strain field and the elastic strain field obtained experimentally. While activated slip systems and total strains are reasonably well predicted, elastic strains appear overestimated next to the grain boundary. This suggests that conventional crystal plasticity models need improvement to correctly model stresses at grain boundaries.

Polyetherketoneketone (PEKK) is of increasing interest for the manufacture of composites in the aeronautical field. It is essential to evaluate the PEKK absorption of fluids, especially water, with which it may come into contact during its processing and use. In this work, we provide for the first time water transport parameters such as water diffusivity and solubility for PEKK in amorphous and semicrystalline states using water immersion as well as dynamic vapor sorption (DVS) experiments. Water diffusion is modeled using Fick’s second law with variable boundary conditions, taking into account possible relative humidity variation during the DVS experiments. Based on similar characterizations of PEEK, we discuss the fact that PEKK absorbs more water than PEEK in terms of polarity.

An original methodology using Digital Image Correlation (DIC) has been designed to precisely measure full-field shrinkages of injection molded polymer plates and then to give the opportunity to compare quantitatively extensive numerical simulations to experiments. The principle of the methodology is based on the full-field strain determination between a reference image of the mold and that of injection-molded parts, which are 275 × 100 × 2.2 mm3 plates. To allow for DIC calculation, 50 µm-depth engravings were machined by electro-discharge process at the surface of the mold. The result of the analysis is a 2D full-field shrinkage map over the whole plate surface (i.e. flow and transverse), with a standard deviation of 0.03%. The marking density has been shown to have a roughly linear influence on the precision of shrinkage measurement. This methodology allows the quantification of the effect of several injection parameters on in-plane shrinkage fields: holding pressure, injection flow rate and direction, geometry of injection gates, or geometrical constraints. Once the best set of parameters of material constitutive laws is identified for the simulation of polymer plates, the simulation procedure is ready to be applied on more complex 3D geometries.