Reference strength values to design against static and fatigue loading polylactide additively manufactured with in‐fill level equal to 100%

Abstract

The aim of this paper is to provide a quantitative examination of the state‐of‐the‐art knowledge of the static and fatigue behaviour of additively manufactured (AM) polylactide (PLA). To this end, existing literature was reviewed, and a number of data sets were extracted and re‐analysed in terms of static strength and standard S‐N curves. As long as objects are 3D‐printed flat on the build plate, printing direction appears to have little effect on the mechanical behaviour of AM PLA, therefore stress/strain analysis can be performed effectively by simply treating this polymer as a linear‐elastic, homogenous, and isotropic material. If static strength cannot be determined experimentally, a conservative reference value of 22 MPa is suggested as being used in situations of practical interest. As far as fatigue is concerned, findings from post‐processing reveal that non‐zero mean stresses can be modelled by simply using the maximum stress in the cycle. According to the statistical re‐analysis discussed in the paper, a reference fatigue curve for the design of AM PLA subjected to uniaxial cyclic loading (for a probability of survival larger than 90%) can be defined by taking the negative inverse slope equal to 5.5 and the endurance limit (at 2·106 cycles to failure) equal to 10% of the material ultimate tensile strength.