Indentation size effects in poly(methyl methacrylate) (PMMA) were studied through nanoindentation. Two factors of indentation size effects in PMMA, namely yield criterion and shear transformation-mediated plasticity, were analysed in detail. The yield criterion that considers strength differential (SD) effects and pressure sensitivity was constructed by performing the combined shear-compression experiments. The relationship between hardness and normal stress can then be obtained based on Tabot’s relation. Shear transformation-mediated plasticity was also applied to model the measured hardness as a function of the indentation depth at different strain rates. Results show that the yield criterion contains the terms of SD effects and pressure sensitivity gives the best description of the yielding of PMMA. Additionally, the volume of single shear transformation zone calculated through the presented criterion agrees well with simulation and exhibits increases with increasing strain rate. Indentation size effects in PMMA under different strain rates were discussed and an appropriate indentation depth range was suggested for calculating the hardness and modulus.

Recent methods for video question answering (VideoQA), aiming to generate answers based on given questions and video content, have made significant progress in cross-modal interaction. From the perspective of video understating, these existing frameworks concentrate on the various levels of visual content, partially assisted by subtitles. However, audio information is also instrumental in helping get correct answers, especially in videos with real-life scenarios. Indeed, in some cases, both audio and visual contents are required and complement each other to answer questions, which is defined as audio-visual question answering (AVQA). In this paper, we focus on importing raw audio for AVQA and contribute in three ways. Firstly, due to no dataset annotating QA pairs for raw audio, we introduce E-AVQA, a manually annotated and large-scale dataset involving multiple modalities. E-AVQA consists of 34,033 QA pairs on 33,340 clips of 18,786 videos from the e-commerce scenarios. Secondly, we propose a multi-granularity relational attention method with contrastive constraints between audio and visual features after the interaction, named MGN, which captures local sequential representation by leveraging the pairwise potential attention mechanism and obtains global multi-modal representation via designing the novel ternary potential attention mechanism. Thirdly, our proposed MGN outperforms the baseline on dataset E-AVQA, achieving 20.73% on WUPS@0.0 and 19.81% on BLEU@1, demonstrating its superiority with at least 1.02 improvement on WUPS@0.0 and about 10% on timing complexity over the baseline.

The polymethyl methacrylate (PMMA) subjected to hygrothermal aging was applied to nanoindentation tests under different indentation strain rates. The influences of hygrothermal aging on the indentation behaviors of PMMA are discussed. Results show that the indentation elastic modulus and hardness decrease with increasing aging time. Furthermore, the indentation size effects (ISE) can be observed in aged PMMA specimens as they are sensitive to aging time as well as to the indentation strain rate. The quantitative analysis of ISE is proposed on the basis of shear transformation-mediated plasticity and was presented in our companion paper.

Titanium Ti6Al4V alloy is a superior material that has extremely high strength, hardness and good anti-corrosion resistance. Dynamic shear-compression experiments were carried out on the alloy to investigate the micro-mechanisms of adiabatic shear banding (ASB) formation. The split Hopkinson pressure bar (SHPB) setup were used for the tests at high strain rates. It was found that the shear deformation localization (SDL) was considerably affected by the complex loading conditions. The micro-mechanisms for the ASB formation relied on different shear compressive proportion of loadings (SCLPs). Scanning electron microscope (SEM) observations showed that the ASB width was related with the SCLP and the fracture failure of alloy was induced by the nucleation and growth of microvoids. In transmission electron microscope (TEM) analysis, the microstructural changes of material within the ASB were characterized by dynamic recrystallization (DRX) and twining grain formation, dislocation migration, and stacking and grain refining processes. The results in this article demonstrates a complex image of microstructural evolution of alloy in the shear localization process.