<p>In this paper, the effect of various additive manufacturing processing parameters on thermoplastic polyurethane's mechanical properties and the durometer hardness testing were evaluated. Additive manufacturing of thermoplastics is a rapidly growing field in many areas, from hobbyists to manufacturing industries.&nbsp; Parts are built layer by layer following the slicing software settings that convert a 3D object into a group of 2D regions that resembles CNC code. There is a need to understand how the mechanical properties are affected by the process parameters compared to traditional injection molding manufacturing. A material testing machine is a traditional equipment to test mechanical properties resulting in the development of a stress-strain curve, where materials are tested until fracture. Indentation hardness testing is another technique that allows nondestructive testing, where for metals, there is a correlation with tensile strength using portable and lower-cost equipment. This work is novel in that it explores the relationship between tensile strength and durometer hardness testing for thermoplastic polyurethane. This thermoplastic has use in many automotive industry applications and consumer products because of its elasticity and high abrasion resistance. A generic thermoplastic polyurethane, also known as flexible TPU, with Shore A durometer hardness of 95 was used for this task. Parameters as the number of shells (thickness of the external wall), the infill (density), and the flowrate (deposition rate) were varied for both tensile and durometer hardness testing. Tensile tests were performed on an Instron 5965 Universal Testing Machine following the ASTM D638-14 standard, while the durometer hardness tests used the ASTM standard D2240 for a type A hardness. Tension testing allows for the determination of properties, such as the tensile stress, tensile strain, modulus, and load at the breaking point, among others, to evaluate the influence of the 3D printing parameters. The durometer hardness testing was compared to establish a relationship between the tension tests and the printing settings. &nbsp;3D printing settings were varied to evaluate the change in mechanical properties. Durometer hardness testing shows the variability of up to 12 Shore A depending on which face was measured (facing the heated bed or facing the opposite face), and tensile testing shows a tensile strength up to 48 MPa. Infill percentage does not influence the tensile strength as much as the flow rate. Low flow rate was found to have the most dramatic change in mechanical properties, up to 20 MPa drop in tensile strength. The durometer hardness testing does not reflect this since it measures discrete points. This paper's results show the first reported mechanical properties for a generic flexible TPU, including a correlation of tensile strength and durometer hardness testing.</p>

Mechanical Properties and Durometer Testing Relationship of Thermoplastic Polyurethane

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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