  Rapid prototyping is an emerging technology for the fast make of engineering
components. A common technique is to laser cut a two-dimensional (2D) part from
polymethyl methacrylate (PMMA) sheet. However, both manufacturing defects and
design defects (such as stress raisers) exist in the part, and these degrade
its strength. In the present study, a combination of experiment and finite
element analysis is used to determine the sensitivity of the tensile strength
of PMMA hexagonal lattices to both as-manufactured and as-designed defects. The
as-manufactured defects include variations in strut thickness and in Plateau
border radius. The knockdown in lattice tensile strength is measured for
lattice relative density in the range of 0.07 to 0.19. A systematic finite
element (FE) study is performed to assess the explicit role of each type of
as-manufactured defect on the lattice strength. As-designed defects such as
randomly perturbed joints, missing cells, and solid inclusions are introduced
within a regular hexagonal lattice. The notion of a transition flaw size is
used to quantify the sensitivity of lattice strength to defect size.
