Abstract This study aims at presenting a new analysis method for adhesive (interfacial) and cohesive (bulk) failures in aluminum (Al) and high-density polyethylene (HDPE) sandwich composites. The samples were submitted to tensile strength tests, according to ASTM C297 so as to obtain the pull-off stresses. The delaminated aluminum surfaces were analyzed with SEM/EDS (Scanning Electronic Microscopy with Energy Dispersive Scanning). The images were calculated using a genetic algorithm (GA), where the areas with cohesive and adhesive failures were identified by the presence or absence of organic compounds. The proposed method also uses the data from the pull-off tests to determine the stress values of adhesion and cohesion separately. Applying the new method, the mean stress of cohesion was 4.17 MPa, and for adhesion it was 0.57 MPa. Thus, it was possible to distinguish and calculate the failure stresses applied to metal/polymer composites.

In the present study, a methodology is appliedfor system reliability based design optimization (RBDO) to thin copper films that are deposited on flat surfaces of polypropylene polymer. The input data of the design of such polymer-metal joint was determined by the necessary normal stress to detach the copper film from the substrate of polypropylene by different forces and interface areas, obtained from uniaxial tensile test. The RBDO methodology was implemented in order to find the smallest bonding area required to assure different reliability levels, minimizing the detaching probability and cost (lower amount of the metallic film). The reliability level is treated as input data and considered as a constraint in the optimization problem. The used optimization methodology is the Genetic Algorithm (GA). This choice is due to the fact that GA presents good behavior when dealing with functions that may exhibit nonlinear behavior. The results shows that the applied methodology is efficient and it is concluded that high reliability requirements might impose larger areas. In the case of 98% of the reliability cases in not detaching the thin film, the resulted bonded area is 3.18 greater than the initial value without safety requirements.

En el presente estudio se aplica una metodología para la optimización de los sistemas basados en la confiabilidad (RBDO) a las películas delgadas de cobre que se depositan en una superficie plana de polímero de polipropileno. Se determinaron los datos de entrada, como el tamaño de la junta por la tensión normal necesaria para separar la película de cobre del sustrato de polipropileno por diferentes fuerzas y zonas de interfaz, que se obtiene a partir de un ensayo de tracción uniaxial. La metodología RBDO se implementó con el fin de encontrar la zona de unión más pequeño requerido para asegurar diferentes niveles de confiabilidad, reduciendo al mínimo la probabilidad de desprendimiento y el costo (menos cantidad de película metálica). El nivel de confiabilidad es tratado como datos de entrada y considerado como una restricción en el problema de optimización. La metodología de la optimización es el algoritmo genético (GA). La elección de esta metodología se debe al buen comportamiento en las funciones que pueden exhibir un comportamiento no lineal. Los resultados muestran que la metodología aplicada es eficiente y se concluye que los requisitos de alta confiabilidad pueden imponer zonas de colaje considerablemente más grandes. En el 98% de los casos de confiabilidad en la no separación de la película fina, resultó en una zona de unión que es 3,18 mayor que el valor inicial sin requisitos de seguridad.

The focus of this paper is to establish a characterisation method for seven polyamide (PA) grades to determine the major material to manufacture an automotive worm gear. The composite properties were measured according to the worm gear loadings: tensile strength, Young's modulus, abrasion and impact resistance. They were also correlated to the PA moisture absorption and its glass fibre (GF) reinforcement. The data from mechanical tests were applied in the finite element analysis (FEA) using the von Mises stress criterion. Before the rig tests of the PA worm gears, the injection process was evaluated, through the capillary rheometry. A higher difficulty to process PA 6/6 30% GF was found, due to its lower apparent viscosity. In the end, the influence of moisture absorption was as decisive to the gear's material selection as the GF to the pinion. Thus, the PAs with the best performance were: PA 6 with 30% GF (gear) and with PA 60% GF (pinion).