Influence of constituent properties and geometric form on behavior of woven fabric reinforced composites

Th potential for woven fabric composite forms to increase the interlaminar strength and toughness properties of laminated composite septems is studied. Experimental and analytical studies were performed on a z-axis fabric

Behavior of composite bolted joints at elevated temperature

Experimental results from an investigation which examines the combined effects of temperature, joint geometry and out-of-plane constraint upon the response of mechanically fastened composite joints are presented. Data are presented for simulated mechanically fastened joint conditions in two laminate configurations fabricated from Hercules AS/3501-6 graphite-epoxy. Strength and failure mode results are presented for the test temperatures of 21 C, 121 C and 177 C and for a range of the geometric parameters W/D and e/D from 3.71 to 7.43 and 1.85 to 3.69, respectively. A hole diameter, D of 5.16 mm was utilized for all tests. Pin bearing tests with out-of-plane constraint were conducted at room temperature only. All elevated temperature data were generated for pin bearing conditions. Ultrasonic C scan inspection of the failed specimens was employed to assess the damage region and to determine failure mode. Comparative data are presented for pin bearing and out-of-plane constraint conditions for the above mentioned joint configurations. The joint under pin loading was modeled by two dimensional finite element methods. Predicted net section strain concentrations were compared with experimental results

Long discontinuous fiber composite structure: Forming and structural mechanics

Cost effective composite structure has motivated the investigation of several new approaches to develop composite structure from innovative material forms. Among the promising new approaches is the conversion of planar sheet to components of complex curvature through sheet forming or stretch forming. In both cases, the potential for material stretch in the fiber direction appears to offer a clear advantage in formability over continuous fiber systems. In the present study, the authors have established a framework which allows the simulation of the anisotropic mechanisms of deformation of long discontinuous fiber laminates wherein the matrix phase is a viscous fluid. The initial study focuses upon the establishment of micromechanics models for prediction of the effective anisotropic viscosities of the oriented fiber assembly in a viscous matrix. Next, the developed constitutive relation is employed through an analogy with incompressible elasticity to exercise the finite element technique for determination of local fiber orientation and laminate thickness after forming. Results are presented for the stretch bending of a curved beam from an arbitrary composite laminate and the bulging of a clamped sheet. Structural analyses are conducted to determine the effect of microstructure on the performance of curved beams manufactured from long discontinuous fiber composites. For the purposes of this study, several curved beams with ideal and non-ideal microstructures are compared for response under pure bending. Material parameters are determined from a separate microstructural analysis

НЕ ПРЕВРАТИТСЯ ЛИ ЕВРОПА В ЕВРАБИЮ

Will Europe become Eurabia?Не превратится ли Европа в Еврабию

Mechanically fastened joints in woven fabric composites

Strength analysis for composite bolted joints involves the mating of a stress analysis with an appropriate mode specific failure criterion for each of the primary failure modes. The stress analysis and failure criteria are independent of each other and can be manipulated separately in order to optimize the strength analysis package formed by their coupling. Material properties tests were conducted on rubber toughened graphite-epoxy material to measure the basic strength and stiffness in the warp and fill directions and in shear. Test matrices are summarized for investigations of laminate configuration, stacking sequence, fastener diameter, edge distance, fastener half spacing, laminate thickness, and fastener torque. A three dimensional finite element analysis computer program was written and failure criteria for net tension, shearout, and bearing were determined

The impact of the Arab Spring on democracy and development in the MENA region

© 2019 John Wiley & Sons Ltd. In evaluating the consequences of the Arab Spring 8 years later, this paper not only focuses on the short-term consequences of the uprisings that swept through a number of countries in the Middle East and North African region but also analyzes the long-term prospects for democratization and development in the MENA region. The impact of the Arab Spring, despite its promises and the expectations of the rest of the world, has been dismal. While only Tunisia made a successful transition to a democratic polity with a constitution guaranteeing the basic rights of the people, the rest of the Arab Spring countries remain in the grip of the authoritarian rule, and countries such as Syria, Libya, and Yemen have been degenerated into bloody civil wars with dwindling hope of peace and freedom. On economic front, the growth has been tardy, showing little difference with countries that were unaffected by the Arab Spring. Yet, the paper concludes, echoing historian Eric Hobsbawm\u27s view, that revolutionary outcomes need not be judged as failure too quickly as they are likely to be partial success in the long term. The impact may be observed in the area of social opening, newer class alliances, and the emergence of a less rapacious, reformed, hybrid authoritarianism

Conspiracy theories as part of history: The role of societal crisis situations

In the present contribution we examine the link between societal crisis situations and belief in conspiracy theories. Contrary to common assumptions, belief in conspiracy theories has been prevalent throughout human history. We first illustrate historical incidents suggesting that societal crisis situations—defined as impactful and rapid societal change that calls established power structures, norms of conduct, or even the existence of specific people or groups, into question —have stimulated belief in conspiracy theories. We then review the psychological literature to explain why this is the case. Evidence suggests that the aversive feelings that people experience when in crisis—fear, uncertainty, the feeling of being out of control—stimulate a motivation to make sense of the situation, increasing the likelihood of perceiving conspiracies in social situations. We then explain that after being formed, conspiracy theories can become historical narratives that may spread through cultural transmission. We conclude that conspiracy theories originate particularly in crisis situations, and may form the basis for how people subsequently remember and mentally represent a historical event