Abstract

The scale effect in Composite Materials is known as the delay in the appearance of damage in the weakest laminas of a laminate (typically 90 degrees laminas). The availability of ultra-thin plies, of up to 20 microns of thickness, has attracted the attention on this effect, as the use of these plies can imply the delay of the onset of damage at a laminate in a significant manner. The frame of the present work is a micromechanical study of the different phases of damage assumed to lead to the failure of the weakest lamina. Thus, it is assumed that the damage starts by isolated debondings between fibres and matrix, then continuing by the abandon of the interphase, the debonding crack kinking into the matrix, and finally the damage progressing either through the matrix itself or along the interfaces between fibres and matrix, to generate a transversal crack in the 90 degrees lamina. The study is carried out using a multi-scale model based on the Boundary Element Method, with control cells in which the damage at micromechanical level previously described is allowed. Concepts derived from Fracture Mechanics and Interfacial Fracture Mechanics are applied in the analysis. The conclusions obtained with this study are compared with those that clearly manifest the scale effect based on a global energy balance from the pristine state to the final situation with the 90 degrees lamina having a complete transverse crack.

Abstract

Soft exoskeletons are lightweight robotic devices currently used for physical therapy and rehabilitation. Most of the current research on soft exoskeletons has focused on the adult population, providing limited options for infant physical therapy and rehabilitation. Spina bifida, a condition affecting the infant’s brain and spinal cord, requires muscle movement treatment through physical therapy. Coupling physiological infant movement with soft robotics can provide solutions for rehabilitation and physical therapy. This study couples joint kinematics from a novel musculoskeletal model with a soft-robotic exoskeleton that uses vacuum-powered artificial muscles. The accuracy of the exoskeleton is assessed when replicating physiological infant kicks. Knee joint kinematics from the musculoskeletal model during infant movement were used to drive the soft exoskeleton. Preliminary results showed that the robotic system replicated infant kicks with lower frequency and small ranges of motion (RMS < 2 degrees) more accurately than those with higher frequency and large ranges of motion (RMS > 6 degrees). The proposed framework has the potential to replicate physiological infant kicks that could be used for infant physical therapy and rehabilitation.