Interlayer Bonding Capability of Additively Manufactured Polymer Structures under High Strain Rate Tensile and Shear Loading

Abstract

Additive manufacturing of polymers via material extrusion and its future applications are gaining interest. Supporting the evolution from prototype to serial applications, additional testing conditions are needed. The additively manufactured and anisotropic polymers often show a weak point in the interlayer contact area in the manufacturing direction. Different process parameters, such as layer height, play a key role for generating the interlayer contact area. Since the manufacturing productivity depends on the layer height as well, a special focus is placed on this process parameter. A small layer height has the objective of achieving better material performance, whereas a larger layer height is characterized by better economy. Therefore, the capability- and economy-oriented variation was investigated for strain rates between 2.5 and 250 s−1 under tensile and shear load conditions. The test series with dynamic loadings were designed monitoring future applications. The interlayer tensile tests were performed with a special specimen geometry, which enables a correction of the force measurement. By using a small specimen geometry with a force measurement directly on the specimen, the influence of travelling stress waves, which occur due to the impact at high strain rates, is reduced. The interlayer tensile tests indicate a strain rate dependency of additively manufactured polymers. The capability-oriented variation achieves a higher ultimate tensile and shear strength compared to the economy-oriented variation. The external and internal quality assessment indicates an increasing primary surface profile and void volume content for increasing the layer height.

Significant Shear Failure Difference among Additively Manufactured Polymers Using Different Techniques

“…Of course, the actual shear failure process in this study was extremely complicated; so, our purpose was to promote immediate interest from interdisciplinary researchers. Specifically, not many studies have focused on the shear failure of 3D printing polymers [ 11 , 12 , 13 ]. Our future work will be focused on the shear crack propagation of the same PA12 material, but the specimens will be made with SLS and FDM.…”

Nonlinear Impact Force Reduction of Layered Polymers with the Damage-Trap Interface

“…With the fast development of additive manufacturing [32,33], our basic research work can be easily used for practical applications. For example, during a multi-material 3D printing process, several polymer layers are printed first, then a DTMI layer is printed before more polymer layers are printed above the DTMI layer.…”

“…Simplified contact mechanics analysis showed that the low Young's modulus of the added adhesive layer is one of the key parameters to reducing the maximum impact force in layered polymers, which leads to dynamic crack arrest at interfaces. Therefore, an efficient material design principle was proposed to develop future material sys- With the fast development of additive manufacturing [32,33], our basic research work can be easily used for practical applications. For example, during a multi-material 3D printing process, several polymer layers are printed first, then a DTMI layer is printed before more polymer layers are printed above the DTMI layer.…”