Elastic tensor stiffness coefficients for SLS Nylon 12 under different degrees of densification as measured by ultrasonic technique. http://dx.doi.org/10.1108/13552540810907929

Abstract

Purpose – In the present investigation the elastic tensor based on the engineering constants of sinterized Nylon 12 is characterized, which is modeled considering a transversely isotropic behavior as a function of apparent density (relative mass density).
Design/methodology/approach – The ultrasound propagation velocity measurement through the material in specific directions by means of the pulse transmission method was used, relating the elastic tensor elements to the phase velocity magnitude through Christoffel’s equation. In addition conventional uniaxial tensile tests were carried out to validate the used technique. Laser sintering of Nylon 12 powder (Duraform PA) has been performed at different laser energy densities, fabricating cube shaped coupons as well as dogbone flat coupons, using a SLS 125 beta machine.
Findings – Correlations for each one of the Young moduli, Shear constants and Poisson’s ratios, presenting an exponential behavior as a function of the sintering degree, were generated. In addition, as the apparent density reaches a maximum of 977 kg/m3 with an energy density of 0,032 J/mm2, the material behaves in an almost isotropic form, presenting average values for the Young modulus, Shear modulus and Poisson’s ratio corresponding to 2310 MPa, 803 MPa and 0,408 respectively.
Research limitations/implications – This research is limited only to one type of material within the elastic range. Validation of one Young modulus measured along one direction only is performed using a tensile test machine, due to the difficulties in evaluating Poisson’s ratios and Shear moduli using conventional tests.
Practical implications – The results presented can be applied to virtual design and validation processes such as Finite Element Analysis.
Originality/value – This paper incorporates detailed information respect to the complete elastic characteristics of Nylon 12 including additional measurements of the Shear moduli and Poisson’s ratios, those that had not been studied yet.