Effect of stretching angle on the stress plateau behavior of main-chain liquid crystal elastomers

Stretching angle for a main-chain liquid crystal elastomer has pronounced effects on the width of the stress plateau as well as the ultimate elongation, while it has no effect on the plateau height.

Experimental Analysis and Optimization to Maximize Ultimate Tensile Strength and Ultimate Elongation of Friction Stir Welded AA6082 Aluminum Alloy

Friction stir welding (FSW) is a well-established welding technique, which allows joining abutting surfaces by generating heating through a rotating and translating tool specifically shaped. Differently from the conventional techniques, continuous welding processes can be executed by FSW, thus supporting the economy of scales objectives. This paper deals with the selection of the optimal process parameters for the FSW of the AA6082 aluminum alloy. Three welding parameters, namely tool plunging, rotational speed and welding speed, have been handled as independent variables for developing two mathematical models by means of a non-linear regression-based approach, with the aim of predicting both ultimate tensile strength and ultimate elongation of the welded joints. A set of additional experimental tests has been used to validate the mentioned metamodels and finally three different metaheuristic algorithms have been implemented for selecting the best process parameters able to maximize the aforementioned mechanical properties. A comparison analysis based on further experimental tests confirmed the accuracy of the predicting metamodels and the quality of solutions yielded by the proposed optimization approaches.

The Influence of the Structure Parameters on the Extensibility of Woven Fabrics

Fabric deformation properties considerably depend on its structure. Garment elasticity is an important factor that allows a garment wearer to move freely. Fabric deformation depends on the structure parameters of yarrn and fabric. It has been known that elongation at break of fabric with elastane yarn is higher than of ordinary fabric. The aim of this work was to analyse elongation at break parameters of the and warp and weft yarn in fabrics. Ten commercially produced samples of woven fabrics were used in the experiment. Some samples were with elastan yarn in the warp and weft directions or only in the weft direction. Elongation at break was measured applying a standard method. The results showed that elongation at break of the main elastic component or another component may occur simultaneously when an elastic component or elastane yarn may reach fabric ultimate elongation.

Fatigue Delamination Crack Growth of Potting Compounds in PCB/Epoxy Interfaces Under Flexure Loading

Electronics components operating under extreme thermo-mechanical stresses are often protected with underfills and potting encapsulation to isolate the severe stresses. By encapsulating the entire PCB, the resin provides complete insulation for the unit thereby combining good electrical properties with excellent mechanical protection. In military and defense applications these components are often subjected to mechanical shock loads of 50,000g and are expected to perform with reliability. Due to the bulk of material surrounding the PCB, potting and encapsulation resins are commonly two-part systems which when mixed together form a solid, fully-cured material, with no by-products. The cured potting materials are prone to interfacial delamination under dynamic shock loading which in turn potentially cause failures in the package interconnects. The study of interfacial fracture resistance in PCB/epoxy potting systems under dynamic shock loading is important in mitigating the risk of system failure in mission critical applications. In this paper, three types of epoxy potting compounds were used as an encapsulation on PCB samples. The potting compounds were selected based on their ultimate elongation under quasi-static loading. Potting compound, A is a stiffer material with 5% of ultimate elongation before failure. Potting compound, B is a moderately stiff material with 12% ultimate elongation. Finally, potting compound C is a softer material with 90% ultimate elongation before failure. The fracture properties and interfacial crack delamination of the PCB/epoxy interface were determined using three-point bend loading with a pre-crack at the interface. The fatigue crack growth of the interfacial delamination was characterized for the three epoxy systems. A prediction of number of cycles to failure and the performance of different epoxy system resistance under cyclic bending loading was assessed.

Interfacial Delamination and Fracture Properties of Potting Compounds and PCB/Epoxy Interfaces Under Flexure Loading After Exposure to Multiple Cure Temperatures

Electronics components operating under extreme thermo-mechanical stresses are often protected with conformal coating and potting encapsulation to isolate the thermal and vibration shock loads. Development of predictive models for high-g shock survivability of electronics requires the measurement of the interface properties of the potting compounds with the printed circuit board materials. There is scarcity of interface fracture properties of porting compounds with printed circuit board materials. Potting and encapsulation resins are commonly two-part systems which when mixed together form a solid, fully cured material, with no by-products. The cured potting materials are prone to interfacial delamination under dynamic shock loading which in turn potentially cause failures in the package interconnects. The study of interfacial fracture resistance in PCB/epoxy potting systems under dynamic shock loading is important in mitigating the risk of system failure in mission critical applications. In this paper three types of epoxy potting compounds were used as an encapsulation on PCB samples. The potting compounds were selected on the basis of their ultimate elongation under quasi-static loading. Potting compound, A is stiffer material with 5% of ultimate elongation before failure. Potting compound, B is a moderately stiff material with 12% ultimate elongation. Finally potting compound C is a softer material with 90% ultimate elongation before failure. The fracture properties and interfacial crack delamination of the PCB/epoxy interface was determined using three-point bend loading with a pre-crack in the epoxy near the interface. The fracture toughness and crack initiation of the three epoxy systems was compared with the cure schedule and temperature. Fracture modeling was performed with crack tip elements in ABAQUS finite element models to determine the crack initiation and interfacial stresses. A comparison of the fracture properties and the performance of epoxy system resistance to delamination was shown through the three-point bend tests. The finite element model results were correlated with the experimental findings.

ULTIMATE ELONGATION OF CONCRETE

It is shown the results of experimental studies of the deformation and concrete fracture process under the axial tension and under the conditions of non-homogeneous state of stress when changing the deformation gradient over the cross section. The test samples were loaded by the short duration load to the point of structural and with load alleviation under the stresses close to destruction. The basic influencing factors on the ultimate elongation of studied types of concrete are found out and the analytical dependences for their description are proposed. The experiments have shown that under the non-uniform stress state the ultimate elongation is not constant; it varies within a wide range and depends on the critical strain gradient. For solving applied problems, the suitable, for practical use, universal form of connection load – deformation was offered, which truly reflects the unity of the relation between stress and deformation of concrete, which is in the condition of homogeneous and non-homogeneous stress states.

The Inhibitory Effect of Polypropylene Fibers towards the Shrinkage of Cement Based Material

At present, polymers, fiber and other additives are added to the cement based materials by researchers at home and abroad for the purpose of dealing with the difficult problems occur in practical application, such as low tensile strength, small ultimate elongation, remarkable brittleness, easy to crack and other issues. In this paper, the shrinkage deformation of cement based materials are classified into four types upon the analysis of shrinkage reasons, then the inhibitory effect and its mechanism of polymers fiber for cement based material are investigated.

Study on Conductive Polypyrrole/P(Ba-co-Aa)-g-PMMA-GMA Composites

A novel PPy/P(BA-co-AA)-g-PMMA-GMA (terpolymer) composites were prepared and the preparation conditions, characterization and properties of the composites were investigated. The results indicate that the oxidant types, molar ratio of oxidant/monomer, polymerization time, PPy content affect greatly the conductivity of the PPy/terpolymer composites. The ultimate elongation of composites decreases with increasing PPy content,while high PPMM content brings forth high tensile strength.

The Conductive of Composites Made from Polypyrrole and PBA-g-PMMA-GMA

A novel PPy/PBA-g-PMMA-GMA (copolymer) composites were prepared and the preparation conditions, characterization and properties of the composites were investigated. The results indicate that the oxidant types, molar ratio of oxidant/monomer, polymerization time, PPy content affect greatly the conductivity of the PPy/terpolymer composites. The ultimate elongation of composites decreases with increasing PPy content,while high PPMM content brings forth high tensile strength.