Two mesomechanics models were analyzed in an attempt to reveal the relationship between stored energy and back stress. It has been indicated that the portion of elastic stored energy due to residual microstresses (E_SR) is closely related to intergranular back stress (X_inter), and the stored energy of dislocations inside grains (E_SD) can be estimated with the plastic work of intragranular back stress (X_intra). Then, the evolution of back stress during cyclic loading was studied, and the plastic work of back stress (W_pB) was calculated with the low cycle fatigue experimental data of Ti-6Al-4V. The result shows that W_pB is partially released at every reverse loading, sufficient to reproduce the evolution of stored energy correctly under cyclic loading. The study also reveals that partially released energy is related to the decrease of X_inter at the initial state of reversal loading resulting from the reduction of the plastic strain incompatibility between grains.

This study resolves the long-standing question of the origin of bilinear Low Cycle Fatigue (LCF) behavior in Ti-6Al-4V using a high-fidelity CPFEM-XFEM framework. We identify that the fundamental origin lies in a fundamental shift in the efficiency of converting macroscopic energy dissipation into microscopic damage. This energetic efficiency is directly governed by the evolution of plastic strain heterogeneity (quantified by the Coefficient of Variation, CV). At low strain amplitudes, high strain localization (high CV) creates a highly efficient “energy funnel,” concentrating dissipated energy into a few critical grains. This manifests physically as a single-crack failure mode, where the crack initiation phase is prolonged, consuming ~80% of the total fatigue life. Conversely, at high strain amplitudes, deformation homogenization (low CV) leads to inefficient, diffuse energy dissipation across many grains. The material must therefore activate a more drastic failure mechanism—multi-site crack initiation and coalescence—to accumulate sufficient damage, reducing the initiation phase to just ~45% of the total life. Therefore, the bilinear C-M curve is the macroscopic signature of this transition from an energetically efficient, localized damage mode to an inefficient, distributed one. This work provides a quantitative, mechanism-based framework for understanding and predicting the complex fatigue behavior of advanced metallic materials.

硅表面固有的菲涅耳反射, 使得硅基半导体光电器件(如太阳能电池、红外探测器)表面有30%以上的入射光因反射而损失掉, 严重影响着器件的光电转换效率. 寻找一种方法降低硅基表面的反射率, 进而提高器件的效率成为近年来研究的重点.本文基于纳米压印光刻技术, 在2 英寸单晶硅表面制备出周期530 nm, 高240 nm的二维六角截顶抛面纳米柱阵列结构. 反射率的测试表明, 当入射光角度为8° 时, 有纳米结构的硅片相对于无纳米 结构的硅片来讲, 在400到2500 nm波长范围内的反射率有很明显的降低, 其中, 800到2000 nm波段的反射率都小于10%, 在波长1360 nm附近的反射率由31%降低为零. 结合等效介质理论和严格耦合波理论对结果进行了分析和验证.

The uncertainties of the used parts bring much difficulties for the decision of the remanufacturing process. Thus, the remanufacturing decision-making framework (RDMF) built on case based reasoning (CBR) is proposed. The formalized knowledge containing the failure conditions is regarded as the input to the reasoning machine and the proper candidate cases that meet the preestablished relevancy calculated by the correlation function can be selected by the first-level reasoning of remanufacturing process and the second-level reasoning of remanufacturing coefficients. The selected candidates remanufacturing cases are then evaluated and modified by the experts in relation to the remanufacturing cost, feasibility and sustainability, and the final remanufacturing process route will be decided on and implemented. Finally, this case will be formulized into the technological procedure and saved to the remanufacturing database for future solution to the remanufacturing process.

—Glass fiber-reinforced composites (GFRP) are prone to undetectable damage, posing challenges to their safe application in aerospace, transportation, and other fields. This study integrated acoustic emission (AE), microscopic visualization, and digital image correlation (DIC) techniques to monitor and quantify damage in multidirectional pre-perforated GFRP laminates under tensile-tensile fatigue loading. It analyzed the intrinsic correlations between surface strain evolution, AE characteristic parameters (amplitude, energy, duration, etc.), and damage modes (matrix cracking, delamination, fiber breakage) of laminates with different fiber orientations, and established the AE-based damage variable D_AE. Its validity was verified using stress-strain curves and damage micromorphology. Results showed that fiber orientation significantly affected the mechanical response and damage behavior of laminates. AE parameters and surface strain effectively characterized damage mechanisms, with obvious differences in strain distribution, stress-strain curves, and AE signals among laminates with different orientations. The engineering error of D_AE for fatigue damage characterization was within 20%, confirming the feasibility of AE technology in quantifying composite fatigue damage and providing key support for composite structural damage monitoring and life prediction.