Experimental and numerical study on the effect of infill pattern on mechanical behaviour of 3D printed rubber-like material

Soft robotics is a fast growing field of research, their inherent softness and flexibility allows for safe interaction with their environment. Soft robotic systems are defined by their compliance, which allows for continuous and often responsive localized deformation. These features make soft robots especially interesting for integration with human tissues, for instance, the implementation of biomedical devices, and for robotic performance in harsh or uncertain environments, exploration in confined spaces or locomotion on uneven terrain.\par To be able to fabricate the soft robots with increasing levels of geometric complexity, new manufacturing methods is needed to be investigated. 3D printing has been gaining traction with their ability to recreate such geometries even with elastomeric materials. These activities should be supported by knowledge on how different settings of process parameters impact the mechanical behavior of the products. However, obtaining this information is a quite complex task given the large variety of possible combinations of materials, 3D printers and slicing software process parameters. \par According to the fact that different printing parameters will affect the mechanical behaviour of the part, in this study the effect of two printing parameters, which are printing infill density and infill pattern, on the mechanical behaviour of a rubber-like elastomer is investigated. The material used in this thesis is one of the most common elastomers in the field of soft robotics, with brand name Ninjaflex. Investigation of mechanical behaviour has been done employing, firstly by determination of the maximum tensile stress and maximum tensile strain at the breaking point for six infill patterns with three infill densities each. In addition to the importance of the maximum tensile stress and strain, understanding the deformation behaviour of the material in the elastic region is significantly crucial in the field of soft robotics. The main reason for this concern is related to actuation and controlling of the soft end-effector. In other words, the information about exact deformation behaviour during loading and unloading of the elastomers in their range of working load will be in input data for inverse kinematics in order to detect the exact position of the end-effector and eventually to actuate the effector to reach the next desired position. This study focuses on three main steps. Firstly, choosing the 3D printing machine and corresponding printing parameters in order to have excellent quality samples. The second step is to determine the maximum tensile stress and maximum tensile strain for samples with six different infill patterns and three different infill densities, performing a tensile test up to the failure point. Eventually, performing a tensile loading and unloading test in the elastic region with for all samples in order to obtain the deformation behaviour and the shape of the loading and unloading curves. The presented results show that printing infill pattern and printing infill density have a significant effect both on the values of the stress and strain at the breaking point and shape of the loading and unloading curves in the elastic region. The project is conducted in the context of a collaboration with Additive design and manufacturing Laboratory at Concordia University, Montreal CA.