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首頁> 外文學(xué)位 >Study of the effect of interface slip and diffusion mechanisms on the creep of metal and intermetallic matrix composites.
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Study of the effect of interface slip and diffusion mechanisms on the creep of metal and intermetallic matrix composites.

機譯：研究界面滑移和擴散機制對金屬和金屬間基復(fù)合材料蠕變的影響。

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Experimental results indicate that, in general, at modest temperatures the creep strength of metal and intermetallic matrix composites is better than that of the matrix material alone. However, at temperatures higher than approximately half the melting temperature of the matrix, the composite strength is limited and in some cases the strengthening imparted by the reinforcements is completely lost despite the absence of any debonding or damage accumulation along the matrix-reinforcement interface. Slip and diffusional flow along the interface, driven by the gradient in the normal stress, are suggested as mechanisms responsible for the loss of strengthening. The composite behavior is investigated by coupling the interface diffusion and slip mechanisms with the power-law creep of the matrix.; The steady state creep strength of a continuous fiber composite under transverse loading and a discontinuous fiber composite under axial loading are investigated. In the case of discontinuous fiber reinforced composites with a diffusive interface, the critical fiber aspect ratio needed for the composite to be stronger than the pure matrix is obtained.; The two relaxation mechanisms are used to explain the temperature dependence of the strength of gamma-TiAl matrix reinforced with Ti 2AlC particles. A methodology is suggested for extracting the properties of the interface combining the experimental measurements of the composite creep strength with the corresponding finite element based strength predictions.; The strength of the leading order singularity and the angular variation of the solution within a constant around the sharp corner of a discontinuous fiber are obtained in an asymptotic study. By comparing the asymptotic and the finite element solutions the value of this constant and the region of dominance for the singular solution are obtained. The region of dominance is found to be only of the order of 5 x 10-4 times the fiber radius.; The influence of the two mechanisms on the transient stress redistribution between the composite constituents is investigated. For a composite whose matrix-reinforcement interface is either perfectly bonded, freely slipping, or rapidly diffusive, the transient solution scales with the applied load and the matrix creep viscous modulus. The transient solutions at large times are found to approach the corresponding solutions obtained from the direct steady state analysis.
機譯：實驗結(jié)果表明，通常，在適中的溫度下，金屬和金屬互化物基體復(fù)合材料的蠕變強度要優(yōu)于單獨的基體材料。然而，在高于基質(zhì)熔化溫度的大約一半的溫度下，復(fù)合材料強度受到限制，并且在某些情況下，盡管沿基質(zhì)-增強界面沒有任何脫膠或損傷累積，但增強劑賦予的增強作用完全消失了。建議由法向應(yīng)力梯度驅(qū)動的沿界面的滑移和擴散流動是造成強度損失的原因。通過將界面擴散和滑移機制與矩陣的冪律蠕變耦合來研究復(fù)合行為。研究了橫向載荷下連續(xù)纖維復(fù)合材料和軸向載荷下不連續(xù)纖維復(fù)合材料的穩(wěn)態(tài)蠕變強度。在具有擴散界面的不連續(xù)纖維增強復(fù)合材料的情況下，獲得了使復(fù)合材料比純基質(zhì)強所需的臨界纖維縱橫比。兩種弛豫機制用于解釋Ti 2AlC顆粒增強的γ-TiAl基體強度的溫度依賴性。建議使用一種方法來提取界面的特性，該方法將復(fù)合蠕變強度的實驗測量結(jié)果與相應(yīng)的基于有限元的強度預(yù)測相結(jié)合。在漸近研究中，獲得了前導(dǎo)奇異性的強度以及溶液在不連續(xù)纖維尖角附近的常數(shù)內(nèi)的角度變化。通過比較漸近解和有限元解，可以得到該常數(shù)的值以及奇異解的支配區(qū)域。發(fā)現(xiàn)主導(dǎo)區(qū)域僅為纖維半徑的5 x 10-4倍。研究了兩種機理對復(fù)合材料成分之間瞬態(tài)應(yīng)力再分布的影響。對于基質(zhì)-增強界面完全粘合，自由滑移或快速擴散的復(fù)合材料，瞬態(tài)溶液隨施加的載荷和基質(zhì)蠕變粘彈性模量成比例增加。發(fā)現(xiàn)大量時間的瞬態(tài)解接近從直接穩(wěn)態(tài)分析獲得的相應(yīng)解。

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