The elasticity problem for a thick-walled cylinder containing a circumferential crack

The elasticity problem for a long hollow circular cylinder containing an axisymmetric circumferential crack subjected to general nonaxisymmetric external loads is considered. The problem is formulated in terms of a system of singular integral equations with the Fourier coefficients of the derivative of the crack surface displacement as density functions. The stress intensity factors and the crack opening displacement are calculated for a cylinder under uniform tension, bending by end couples, and self-equilibrating residual stresses

Transient thermal stress problem for a circumferentially cracked hollow cylinder

The transient thermal stress problem for a hollow elasticity cylinder containing an internal circumferential edge crack is considered. It is assumed that the problem is axisymmetric with regard to the crack geometry and the loading, and that the inertia effects are negligible. The problem is solved for a cylinder which is suddenly cooled from inside. First the transient temperature and stress distributions in an uncracked cylinder are calculated. By using the equal and opposite of this thermal stress as the crack surface traction in the isothermal cylinder the crack problem is then solved and the stress intensity factor is calculated. The numerical results are obtained as a function of the Fourier number tD/b(2) representing the time for various inner-to-outer radius ratios and relative crack depths, where D and b are respectively the coefficient of diffusivity and the outer radius of the cylinder

Thermal shock resistance of ceramic matrix composites

The experimental and analytical investigation of the thermal shock phenomena in ceramic matrix composites is detailed. The composite systems examined were oxide-based, consisting of an aluminosilicate matrix with either polycrystalline aluminosilicate or single crystal alumina fiber reinforcement. The program was divided into three technical tasks; baseline mechanical properties, thermal shock modeling, and thermal shock testing. The analytical investigation focused on the development of simple expressions for transient thermal stresses induced during thermal shock. The effect of various material parameters, including thermal conductivity, elastic modulus, and thermal expansion, were examined analytically for their effect on thermal shock performance. Using a simple maximum stress criteria for each constituent, it was observed that fiber fracture would occur only at the most extreme thermal shock conditions and that matrix fracture, splitting parallel to the reinforcing fiber, was to be expected for most practical cases. Thermal shock resistance for the two material systems was determined experimentally by subjecting plates to sudden changes in temperature on one surface while maintaining the opposite surface at a constant temperature. This temperature change was varied in severity (magnitude) and in number of shocks applied to a given sample. The results showed that for the most severe conditions examined that only surface matrix fracture was present with no observable fiber fracture. The impact of this damage on material performance was limited to the matrix dominated properties only. Specifically, compression strength was observed to decrease by as much as 50 percent from the measured baseline

Eficiência de uso da radiação fotossinteticamente ativa em canola sob distintos espaçamentos.

A radiação solar é a fonte primária de energia para vários processos vitais do ecossistema, dentre eles destaca-se o crescimento vegetal e seu acúmulo de fotoassimilados. Neste contexto, a mensuração da radiação fotossinteticamente ativa interceptada (RFAin) por dosséis de plantas e sua interação com as diferentes estruturas da planta, especialmente as folhas, condiciona a capacidade de crescimento e produção

Experimental Comparison of Preferential vs. Common Delta Connections for the Star-Delta Starting of Induction Motors

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Rendimento de grãos de canola sob diferentes ambientes em Santa Maria-RS.

A canola (Brassica napus L. var. oleifera) é uma cultura típica de clima temperado e muito responsiva às condições ambientais, especialmente às condições hídricas. Em função disso, a determinação da data de semeadura mais adequada para cada genótipo é um dos fatores determinantes para alcançar o sucesso produtivo com a cultura