Browsing by Author "Leite, Afonso"
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- Crack onset in stretched open hole PMMA plates considering linear and non-linear elastic behavioursPublication . Leite, Afonso; Mantic, V.; Paris, F.Crack onset in PMMA holed plates subjected to tensile stresses is studied experimentally and by the coupled stress and energy criterion of the Finite Fracture Mechanics (CCFFM). The elastic, strength and fracture properties of PMMA are determined by the standard tests, a clearly nonlinear stress-strain relation being identified in the tensile tests. Thus, a novel numerical implementation of the CCFFM considering a non-linear elastic (NLE) material model, using the Ramberg-Osgood approximation, in addition to the usually used linear elastic (LE) model, is developed. Testing of plates with different hole sizes shows a hole size effect in the nominal failure load as expected. For a better fitting of the experimental results, higher strength values obtained by three point bending (TPB) flatwise and edgewise coupons (without any notch), for these material models, are used, apparently for the first time, in the CCFFM predictions. This approach reflects the observation that the strength values associated to smaller but highly stressed volumes, like those located at stress maxima in the holed plates and TPB specimens, are higher. For finite-width holed plates and both material behaviours, suitable FEM models are developed to implement the CCFFM for both LE and NLE models, considering plane stress state. Moreover, an inverse procedure is devised, using the experimental data for holed plates and predictions by CCFFM, to estimate the strength and fracture properties to be used in both material models, providing very good correlations of the CCFFM predictions with the experimental results.
- Design, control, and testing of a multifunctional soft robotic GripperPublication . Correia, A.; Charters De Azevedo, Tiago; Leite, Afonso; Campos, Francisco M.; Monge, Nuno; Rocha, André; Mendes, Mário J. G. C.This paper proposes a multifunctional soft robotic gripper for a Dobot robot to handle sensitive products. The gripper is based on pneumatic network (PneuNet) bending actuators. In this study, two different models of PneuNet actuators have been studied, designed, simulated, experimentally tested, and validated using two different techniques (3D printing and molding) and three different materials: FilaFlex 60A (3D-printed), Elastosil M4601, and Dragonskin Fast 10 silicones (with molds). A new soft gripper design for the Dobot robot is presented, and a new design/production approach with molds is proposed to obtain the gripper’s PneuNet multifunctional actuators. It also describes a new control approach that is used to control the PneuNet actuators and gripper function, using compressed air generated by a small compressor/air pump, a pressure sensor, a mini valve, etc., and executing on a low-cost controller board—Arduino UNO. This paper presents the main simulation and experimental results of this research study.