Additive manufacturing tensile stress

Fillers are not used to any extent in products made by the rotational molding process. Rotational molding is dominated by polyethylene (close to 90% volume) to which even small addition of pigments or fillers (less than 2 wt%) causes a decrease in tensile and impact properties of the products manufactured in this process. Polyethylene is vulnerable to environmental stress cracking which is made worse if fillers are present. 

Compression stress-strain tests may be conducted if in-service forces are of this type. A compression test is conducted in a manner similar to the tensile test, except that the force is compressive and the specimen contracts along the direction of the stress. Equations 6.1 and 6.2 are utilized to compute compressive stress and strain, respectively. By convention, a compressive force is taken to be negative, which yields a negative stress. Furthermore, because /q is greater than /, compressive strains computed from Equation 6.2 are necessarily also negative. Tensile tests are more common because they are easier to perform also, for most materials used in structural applications, very little additional information is obtained from compressive tests. Compressive tests are used when a material s behavior under large and permanent (i.e., plastic) strains is desired, as in manufacturing applications, or when the material is brittle in tension. 

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