Interface fails and Young's module approximation of multilayer flexible devices through finite element method.

Electronic flexible devices are prone to degrade their electrical performance or lose functionality when subjected to deformations. Brittle fracture is a common damaging effect observed in devices composed of low-thickness layered materials stacked onto a flexible substrate by dissimilar mechanical properties interaction. This work studies the mechanical behavior of Organic Flexible Solar Cells (OFSC) with a heterostructure PET/ITO/P3HT:PCBM/Ag subjected to uniaxial displacements through an experimental and numeric point of view. Experimental showed that damage proceeds in two ways. First, the formation of a grid crack pattern begins at the ITO layer, and second, the delamination in the ITO/P3HT:PCBM interface. The numerical model analyzed the force and displacements and the absorption/dissipation of strain energy on layers and interfaces of the device. The comparison of the global Young's module for experimental and numeric studies validated the numeric analysis, with results of 4.16 ± 0.05 GPa for experimental and 4.36 ± 0.15 GPa for numeric. Additionally, the model associates the ITO layer with the highest strain energy dissipation or the most prone to failure, which agrees with the experiments. Then, the model successfully predicts the mechanical behavior of OFSC and represents a valuable tool for studying flexible devices and predicting the appearance of mechanical damage when subjected to uniaxial deformations, even being able to avoid potential damage changing parameters such as the thickness of the layers.

A quantitative study of the influence of coprocessing of binders on the mechanical properties of paracetamol tablets

A 2³ factorial experimental design has been used to quantitatively study individual and interaction effects of the nature of binder (N), concentration of binder (C) and the applied pressure (P) on two mechanical properties, namely, tensile strength (TS) and brittle fracture index (BFI), of paracetamol tablets. The factorial design was also used to study the quantitative effects of coprocessing of binders on the mechanical properties. The results obtained from this study suggest that the nature (i.e. plastic/elastic) and ratio of binders coprocessed together alter the influence of C and P on TS and BFI.

Utilizou-se planejamento experimental fatorial 2³ para estudar, quantitativamente, os efeitos individuais e de interação da natureza do ligante (N), concentração do ligante (C) e a pressão aplicada (P) em duas propriedades mecânicas, como forças de ruptura (TS) e índice de fragilidade (BFI) de comprimidos de paracetamol. O planejamento fatorial foi, também, empregado para estudar os efeitos quantitativos do coprocessamento de ligantes nas propriedades mecânicas. Os resultados obtidos desse trabalho sugerem que a natureza (plástica/elástica) e a proporção de ligantes coprocessados, juntas, alteram a influência de C e P em TS e em BFI.

Impact and flexural strength, and fracture morphology of acrylic resins with impact modifiers.

OBJECTIVES: This study evaluated the impact and flexural strength and analyzed the fracture behavior of acrylic resins. METHODS: Eighteen rectangular specimens were fabricated of Lucitone 550, QC 20 (both unreinforced acrylic resins), Impact 1500 (extra strength impact), Impact 2000 (high impact) according to the manufacturers' instructions. The impact strength was evaluated in notched specimens (50x6x4mm) and flexural strength in unotched (64x10x3.3mm), using three-point bending test, as well as, stress at yield, Young modulus and displacement at yield. Fragments from mechanical tests were observed by SEM. Data from impact strength, stress at yield and displacement at yield were analyzed by 1-way ANOVA and Tukey test (alpha=0.05). Young modulus values were analyzed by One-way ANOVA and Dunnett T3 multiple comparisons test (alpha=0.05). RESULTS: Mean values of impact strength and stress at yield values were higher (P<.005) for Impact 2000 while Young modulus was higher (P<.05) for Lucitone 550; Impact 1500 and Impact 2000 showed significant values (P<.05) in the displacement at yield. Impact fractures of the all acrylic resins were brittle. Bending fractures of Lucitone 550 and Impact 2000 were brittle, QC 20 fractures were ductile and Impact 1500 showed brittle (75%) and ductile (25%) fractures. CONCLUSION: Within the limitations of this study, the Impact 2000 showed improved mechanical properties with high capacity of stress absorption and energy dissipation before the fracture.