Everyday work investigations for safety

A key theme in safety is the investigation and improvement of work processes and conditions. This is built on a tradition of studying accidents, but there is growing interest in the investigation of everyday work. Researchers have started using terms such as success, normal and everyday work investigations, but behind these can be different activities. This paper makes explicit some considerations behind investigations of everyday work, how these considerations shape an investigation, and how they reflect different schools of thought. These considerations can be used as an aid for designing everyday work investigations for safety and serve as a first step towards critical reflection on investigating everyday work.     

Elastic modulus of nanocrystalline cemented carbide

The purposes of this work were to obtain the accurate elastic modulus of the nanocrystalline WC–Co cemented carbides, and to propose the mechanism for the difference of elastic modulus between the nanocrystalline and conventional polycrystalline cemented carbides. The nanocrystalline cemented carbide was prepared by spark plasma sintering (SPS) technique. The conventional polycrystalline cemented carbides were prepared by SPS and sinter-HIP techniques as references, respectively. The sintered cemented carbides were characterized by X-ray diffractometry, scanning electron microscopy and the transmission electron microscopy with precession electron diffraction technology. The elastic modulus was obtained by averaging the values measured with the continuous stiffness measurement method of the nanoindentation technology. The results show that the nanocrystalline cemented carbide has a relatively low modulus, which could be attributed to the more interface area and higher fraction ratio of the hcp cobalt phase caused by the rapid heating and cooling process during SPS.     

汽车用钢弹性模量测试探讨

采用静态拉伸试验方法对系列汽车用钢材料进行测试，得到了汽车用钢材料的弹性模量，分析了强化方式、轧制方向、塑性变形等对材料弹性模量的影响。结果表明：强化方式影响材料的弹性模量，固溶强化的汽车用钢材料弹性模量最大；材料的弹性模量表现出各向异性特点，垂直于轧制方向的弹性模量最大；塑性变形降低材料的弹性模量。研究结果为工程设计、冲压模拟、碰撞模拟、回弹模拟等提供计算依据。     

纳米压痕法研究单晶Al3Sc相的硬度和杨氏模量

使用EBSD和纳米压痕法研究毫米级块状单晶Al₃Sc对应的取向、硬度和杨氏模量。试验结果表明,选用过共晶Al-Sc合金加热至液态后缓慢冷却(60 ℃/h)可以得到毫米级单晶Al₃Sc,通过EBSD和纳米压痕法得到五个不同取向(567)、(139)、(124)、(113)和(144)单晶Al₃Sc的硬度在3.7~4.3 GPa,复合弹性响应模量在143.6~146.1 GPa。对比不同泊松比下各取向的杨氏模量理论值与试验值,发现泊松比为0.188时二者之间差异最小,对应各取向的杨氏模量试验值在157.5~160.6 GPa。     

Elastic modulus prediction based on thermal conductivity for silica aerogels and fiber reinforced composites

The speed of sound is a critical parameter in the test of mechanical and thermal properties. In this work, we proposed a testing method to obtain the elastic modulus of silica aerogel from the sound speed formulas. The solid thermal conductivity of the silica aerogel is experimentally measured for predicting the sound speeds, and then the elastic modulus is calculated based on the elasticity sound speed model. The experimental data of the solid thermal conductivity of silica aerogels with different densities are employed and the obtained elastic modulus is fitted as a power-law exponential function of the density. Two existing sound speed models and three groups of available experimental data are also employed to validate the present fitting relation, and good agreement is obtained for the silica aerogel in the density range of 150–350 kg/m³. The fitting formula can also be extended to estimate the elastic modulus of the glass fiber-reinforced silica aerogel composite. The results show that the elastic modulus of the aerogel composite is sensitive to the glass fiber volume fraction, while the thermal conductivity is weakly dependent on the glass fiber volume fraction at room temperature in the studied range of fiber volume fraction.     

Experimental determination of elastic modulus of elasticity and Poisson’s coefficient of date palm tree fiber

The present study is an attempt to valorize local vegetable fibers by evaluating thire effectiveness as a new composite biomaterial. Our aim was to determine the mechanical characteristics, namely the elastic modulus and Poisson’s coefficient, of a fiber, locally called “Lif,” that is a natural material extracted from different date palm tree varieties in Biskra, a region situated in southeastern Algeria. This study compares the mechanical characteristcs of the Lif date palm tree fiber with other synthetic and plant fibers studied previously.     

Local demand shocks and firms' survival: An application to the Italian economy during the Great Recession

The Italian economy is characterised by a large number of micro-firms and small firms and by a long-lasting gap between North and South Italy. Therefore, global shocks – such as the Great Recession – have had a heterogeneous impact at the local level: the collapse in private demand was unequally distributed across different products, services and regions. The aim of this paper, therefore, is to evaluate the impact of the Great Recession on firm's survival for the universe of Italian firms in the light of two relevant indicators: local exposure to crisis and local demand shocks. The results suggest a strong negative impact of local demand shocks on the survival of firms, whereas the degree of exposure to the crisis generally has a weak effect.     

An investigation of the elastic properties of viscoelastic clusters of particles: A comparison between two methods

Most industrial process lines involve mixing complex dispersions, which can include non-Newtonian liquids and viscoelastic particles. Knowledge of the parameters of these components may provide a key for understanding how dispersions are formed and how equipment should be designed. One parameter is the shear modulus, which describes the ability of particles to resist mechanical stresses. This parameter may play the main role in the mixing process, when a dispersion is formed by the mechanical influence of a rotor (slice or shear in a rotor-stator mixer). In this work, two methods were chosen for measuring the shear modulus: the evaluation method, based on the Warner-Bratzler cut test, and the oscillatory method. Both methods were used for measuring viscoelastic clusters of particles, and the results were adjusted for the purposes of the comparison. The comparison shows that the shear modulus values obtained from Warner-Bratzler are higher than the values obtained from the oscillatory test for the same conditions. This difference can be explained by differences in the mechanical processes during the experiments.     

A novel constitutive stress-strain law for compressive deformation of the gas diffusion layer

Substantial compressive deformation occurs in the gas diffusion layer (GDL) under the pressure applied during the fuel cell assembly. The GDL deformation has a direct impact on the efficiency and performance of the fuel cell since it leads to the alteration of the GDL microstructure and porosity. This makes the accurate characterization of the GDL compressive behavior crucial for analyzing the fuel cell performance and its optimal design. In this paper, analytical, experimental, and numerical methods have been employed to comprehensively study the constitutive law of the GDL under compression. Starting from the recently developed stress-density relations, the constitutive stress-strain equations are derived for the GDL and the relation between the stress-density and stress-strain laws are revealed. Experimental compression tests have been performed on GDL samples and the capability of the proposed constitutive law in capturing the real behavior of the material has been proved. It has been observed that the simplifying assumption of constant zero Poisson's ratio in the through-plane direction made in many previous studies cannot accurately represent the GDL material behavior and a modification is proposed. The developed constitutive law has been successfully implemented in a finite element model of the GDL-bipolar plate assembly in the fuel cell structure and the variations of the GDL porosity, density, and through-plane Young's modulus and Poisson's ratio have been investigated for different vertical displacements of the bipolar plate.     

Failure load prediction and optimisation for adhesively bonded joints enabled by deep learning and fruit fly optimisation

Adhesively bonded joints have been extensively employed in the aeronautical and automotive industries to join thin-layer materials for developing lightweight components. To strengthen the structural integrity of joints, it is critical to estimate and improve joint failure loads effectually. To accomplish the aforementioned purpose, this paper presents a novel deep neural network (DNN) model-enabled approach, and a single lap joint (SLJ) design is used to support research development and validation. The approach is innovative in the following aspects: (i) the DNN model is reinforced with a transfer learning (TL) mechanism to realise an adaptive prediction on a new SLJ design, and the requirement to re-create new training samples and re-train the DNN model from scratch for the design can be alleviated; (ii) a fruit fly optimisation (FFO) algorithm featured with the parallel computing capability is incorporated into the approach to efficiently optimise joint parameters based on joint failure load predictions. Case studies were developed to validate the effectiveness of the approach. Experimental results demonstrate that, with this approach, the number of datasets and the computational time required to re-train the DNN model for a new SLJ design were significantly reduced by 92.00% and 99.57% respectively, and the joint failure load was substantially increased by 9.96%.