The rapid manufacturing process of selective laser melting has been used to produce a series of stainless steel 316L microlattice structures. Laser power and laser exposure time are the two processing parameters used for manufacturing the lattice structures and, therefore, control the quality and mechanical properties of microlattice parts. An evaluation of the lattice material was undertaken by manufacturing a range of struts, representative of the individual trusses of the microlattices, as well as, microlattice block structures. Low laser powers were shown to result in significantly lower strand strengths due to the presence of inclusions of unmelted powder in the strut cross-sections. Higher laser powers resulted in struts that were near to full density as the measured strengths were comparable to the bulk 316L values. Uniaxial compression tests on microlattice blocks highlighted the effect of manufacturing parameters on the mechanical properties of these structures and a linear relationship was found between the plateau stress and elastic modulus relative to the measured relative density.

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A range of metallic lattice structures were manufactured using the selective laser melting (SLM) rapid prototyping technique. The lattices were based assemblies of repeating unit-cells with their strands oriented at 0°, ±45°, and 90° to the vertical when viewed from the front. Mechanical tests on the strands and the lattice blocks showed that these systems exhibit a high level of reproducibility in terms of their basic mechanical properties. An examination of the compression failure mechanisms showed that the [±45°] and [±45°, 90°] lattices failed in bending and stretching modes of failure, whereas the [0°, ±45°] lattices failed as a result of buckling of the vertical pillars. Sandwich structures were manufactured by binding woven carbon-fiber reinforced plastic to the lattice structures. Subsequent three-point bend tests on these structures identified the principal failure mechanisms under flexural loading conditions. Here, cell crushing, hinge rotation, and gross plastic deformation in the strands were observed directly under the point of loading. Low-velocity impact tests were conducted on the sandwich beams and a simple energy-balance model was used to understand how energy is absorbed by the sandwich structures. The model suggests that the majority of the incident energy of the projectile was absorbed in indentation effects, predominantly in the core material, directly under the steel indenter.

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The results of a series of quasi-static and impact tests on four scale-model sizes of fiber—metal laminate (FML) are compared to a scaling law that predicts response parameters based on a simple geometrical relationship of the input parameters. The FMLs consist of an aluminum alloy and a self-reinforced thermoplastic composite based on polypropylene fibers in a polypropylene matrix. The scaled FML laminates were arranged in a 2/1 configuration, and ply-level scaling of the FML constituent materials was employed to yield specimens with a nominally constant composite volume fraction, as well as correctly scaled in-plane and bending stiffness properties. In the initial part of this experimental program, the tensile and flexural properties of these hybrid materials were investigated at quasi-static rates of loading. Here, no significant scaling effects were observed in the mechanical response of the laminates. Following this, simply-supported scaled beams and plates were subjected to low-velocity impact loading in order to investigate scaling effects in the processes of damage development and target perforation. Here, response parameters such as the target deflection, the impact force, and the damage threshold energy were found to obey the scaling law. It is believed that experimental data of this nature will give greater confidence to engineers involved in the design of components based on hybrid materials such as fiber—metal laminates.

The strain-rate sensitivity of a hot-compacted formed self-reinforced thermoplastic composite, based on polypropylene fibers in a polypropylene matrix, was investigated through a series of quasi-static and dynamic tensile tests. Characterization of the mechanical property dependence on strain-rate for a self-reinforced thermoplastic is an important issue when the material forms one part of a hybrid system, as in the case of a thermoplastic fiber—metal laminate that is prone to localized impact loading events. Strain-rates in the range from quasi-static (10—4 s—1) up to 10 s—1 were achieved in the gauge region of rectangular specimens loaded in a servo-hydraulic test machine. A measurable rate effect was observed in key mechanical properties of the self-reinforced composite, and constitutive equations were successfully applied to characterize the strain-rate behavior of the yield stress. Failure of the longitudinal ply fibers was the dominant failure mechanism, whilst the degree of inter-ply delamination varied over the dynamic loading range.

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