Defects and shape distortions can arise during thermoforming of thermoplastic composites. Design guidelines for thermoplastic composites can help to prevent such defects. The material selection and geometry definition are part of the design guidelines. A test to check the formability of a material is developed as an aid for the material selection. Strips of varying widths are thermoformed inducing double curvature, in order to find the width at which the material starts to wrinkle. The thermoformed strips of quasi-isotropic UD carbon/PEEK and quasi-isotropic 8HS glass/PPS show a clear difference in formability. The UD carbon and the 8HS glass strips develop wrinkles through-the-thickness of the laminate at a width of 40 mm and 90 mm respectively. The test shows good potential to be used as part of the design guidelines.
The frictional performance of several rubbers after pulsed-DC plasma treatments has been examined. In all cases, the treated rubbers showed better performance than the corresponding untreated ones. Stronger treatments, in terms of longer process time and/or higher substrate bias voltage, led to larger reductions of coefficient of friction and wear. The addition of hydrogen to the argon plasma did not show any additional positive effect. Nevertheless, different degrees of improvement were observed for different rubbers. In fact, the energy consumed during the tribotest scales with the maximum working temperature of the rubbers, indicating that the plasma treatment is more effective in the case of more sensitive rubbers.
Standard finite elements can exhibit the numerical artifact of intra-plyshear locking during forming simulations. The displacement fields of elementsare piecewise continuous and cannot correctly capturediscontinuities in the shear field. This shear locking is illustrated insimulations of bias-extension experiments with an unaligned mesh. Two simpletests were developed as a critical indicator of intra-ply shear locking intriangular elements. A single-element-test shows the origin of the locking anda pull-out test indicates locking caused by small misalignments of theelements.
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