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Atomistic Finite Deformation Simulations: a Discussion on Effects of Multi-Axial Loading on Crystal Plasticity of Single- and Poly-Crystalline Nickels

機(jī)譯：原子有限變形模擬：多軸向載荷對(duì)單晶和多晶鎳的晶體可塑性影響的討論

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Embedded Atom Method (EAM), developed by Daw and Baskes [1], is employed to study the crystal plasticity behavior of single crystalline and polycrystalline Ni under bi-axial loading conditions in conjunction with the variations of ambient temperature and loading rates. Recently, EAM has been used to investigate the effects of crystalline structures and orientation to the plastic behavior of metal under shear loading with the influence of multiple length scales and time scales [2-4]. Spatial size scale effect on the yield stress was observed when studying single crystal Ni oriented at <011> [5], in which it was pointed out that the thermodynamic forces in the form of stresses should be used to study the spatial length scale effect in atomistic simulation. According to this concept, the crystal plasticity behavior of single crystalline and polycrystalline Ni under multi-axial loading conditions is implicitly expresses as a function of both loading ratio and rate as well as the variations of ambient temperature and loading rates. It should be noted that special care must be taken when applying boundary conditions to atoms. Extra constraints at edges and/or corners of the sample were found initiating earlier dislocation migration or causing slip along not globally active slip systems.Three spatial size scales were used in this study. The crystal plasticity of the single crystal Ni was studied with the ratio of bi-axial loads set ranging from 1 to 100 along crystalline coordinate [100] and [010]. The initiation of dislocation, the plastic flow and massive dislocation migration were recorded and noted on stress and strain response curve, which will pinpoint the effect of crystal plasticity inside single crystal on the behavior captured by the atomistic simulation. The sample with the least spatial size effect upon crystal plasticity was selected to study the effects of various loading rate and under room and elevated temperatures. Lastly, the same set of study was conducted on polycrystalline Ni. Large variations in plastic flow were observed between single- and poly- crystalline Ni. The effect of crystalline orientations and grain boundary orientations on stress and work hardening were systematically examined on polycrystalline Ni. The atomistic scale results are also qualitatively compared to macro-scale finite element simulations using internal state variables.
機(jī)譯：Daw和Baskes [1]開發(fā)的Embedded Atom Method（EAM）用于研究雙軸加載條件下單晶和多晶Ni的晶體可塑性行為，以及環(huán)境溫度和加載速率的變化。最近，EAM已被用來研究剪切結(jié)構(gòu)在多種長度尺度和時(shí)間尺度的影響下晶體結(jié)構(gòu)和取向?qū)饘偎苄孕袨榈挠绊慬2-4]。當(dāng)研究取向?yàn)?011>的單晶Ni時(shí)，觀察到了空間尺寸尺度對(duì)屈服應(yīng)力的影響[5]，其中指出應(yīng)以應(yīng)力形式的熱力學(xué)力來研究空間長度尺度效應(yīng)。原子模擬。根據(jù)這個(gè)概念，單晶和多晶鎳在多軸載荷條件下的晶體可塑性行為隱含地表示為載荷比和速率以及環(huán)境溫度和載荷率變化的函數(shù)。應(yīng)當(dāng)指出，在對(duì)原子施加邊界條件時(shí)必須格外小心。發(fā)現(xiàn)在樣品的邊緣和/或拐角處存在額外的約束，從而開始了較早的位錯(cuò)遷移或?qū)е卵胤侨只顒?dòng)的滑動(dòng)系統(tǒng)滑動(dòng)。 在這項(xiàng)研究中使用了三個(gè)空間大小尺度。研究了單晶Ni的晶體可塑性，其雙軸載荷比沿結(jié)晶坐標(biāo)[100]和[010]設(shè)置為1到100。記錄了位錯(cuò)的起始，塑性流和大量的位錯(cuò)遷移，并在應(yīng)力和應(yīng)變響應(yīng)曲線上記錄下來，這將查明單晶內(nèi)部晶體可塑性對(duì)原子模擬所捕獲行為的影響。選擇對(duì)晶體可塑性影響最小的空間大小的樣品，以研究各種加載速率以及在室溫和高溫下的影響。最后，對(duì)多晶鎳進(jìn)行了相同的研究。在單晶和多晶鎳之間觀察到塑性流動(dòng)的巨大變化。在多晶鎳上系統(tǒng)地研究了晶體取向和晶界取向?qū)?yīng)力和加工硬化的影響。原子尺度結(jié)果也與使用內(nèi)部狀態(tài)變量的宏觀有限元模擬進(jìn)行了定性比較。

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