Determining the Co-Efficient of End Constraint of Stretch Formed Microtruss Materials

Abstract

Microtruss cellular metals are a class of multifunctional materials, composed of a regular arrangement of supporting struts. They can be fabricated by stretching perforated metal sheets out of plane by applying force at strut intersections. Once fabricated, external loads are resolved axially along the struts resulting in stretch dominated deformation, yielding enhanced weight specific strength and stiffness at lower densities compared to conventional metallic foams. Given the slenderness of the struts making up the microtruss architecture, failure often occurs by inelastic buckling and is therefore dependent on the rigidity of the strut end constraints. During column buckling the limiting conditions are pin jointed (k=1) and rigid jointed (k=2), with microtruss struts typically having end constraints intermediate to these boundaries. Experimental and finite element methods were used to determine the value of k in IN600 microtrusses. Because of the non-linear stress-strain behavior of the parent metal, the relative significance of end constraint uncertainty is a function of the strut slenderness ratios and the material in question.