Abstract
This paper investigates size effects on the mechanical response of additively manufactured lattice structures based on a commercially available polylactic acid (PLA) polymer. Initial attention is focused on investigating geometrical effects in the mechanical properties of simple beams and cubes. Following this, a number of geometrically scaled lattice structures based on the body-centered cubic design were manufactured and tested in order to highlight size effects in their compression properties and failure modes. A finite element analysis was also conducted in order to compare the predicted modes of failure with those observed experimentally. Scaling effects were observed in the compression response of the PLA cubes, with the compression strength increasing by approximately 19% over the range of scale sizes investigated. Similar size-related effects were observed in the flexural samples, where a brittle mode of failure was observed at all scale sizes. Here, the flexural strength increased by approximately 18% when passing from the quarter size sample to its full-scale counterpart. Significant size effects were observed following the compression tests on the scaled lattice structures. Here, the compression strength increased by approximately 60% over the four sample sizes, in spite of the fact that similar failure modes were observed in all samples. Finally, reasonably good agreement was observed between the predicted failure modes and those observed experimentally. However, the FE models tended to over-estimate the mechanical properties of the lattice structures, probably as a result of the fact that the models were assumed to be defect free.
Highlights
In recent years, there has been an unprecedented increase in the use of additively manufactured parts in a range of engineering applications [1,2,3,4,5]
A conti0n.u6omums polylactic acid (PLA) polymer filaLmayenert Tmhaitcekrniaelssis heated and extruded through a0.n5omzzmle according to the parametersDgeivfaeunltinPrTianbtilneg1S. pTeheedmajority of the specimens30w0e0rme pmr/imntiend. along the horizontal orientatIionnfiltloPcerrecaetnetnagoeminally fully dense solid lattice stru1c0t0u%res
Additional square plates with an edge length of 120n mm and a thickness of 4n mm, i.e., similar to the lower baseplate were produced separately and subsequently bonded to the upper surface of the lattice structures using a two-part Araldite epoxy adhesive. This was necessitated by the fact that it was not possible to build the top plates directly on top of the lattice structures during the manufacturing process
Summary
There has been an unprecedented increase in the use of additively manufactured parts in a range of engineering applications [1,2,3,4,5]. Experimental studies on the effects of specimen size on the flexural and tensile properties of carbon fibre–epoxy composite beams tested under scaled loading conditions were conducted by Jackson et al [16,17]. The results were found to be in good agreement with the predicted scaling behaviour over the range of parameters studied Another investigation on the effects of scaling on the strength of notched composite laminates based on a unidirectional carbon-fibre/epoxy prepreg system was conducted by Green et al [22]. They showed that the strength of the composite decreased with increasing specimen size.
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