Predictive environmental hydrogen embrittlement on fracture toughness of commercial ferritic steels with hydrogen-modified fracture strain model

In this work, a practical numerical model with few parameters was proposed for the prediction of environmental hydrogen embrittlement. The proposed method adopts hydrogen enhanced plasticity-based mechanism in a fracture strain model to describe hydrogen embrittlement. Fracture toughness degradation of three commercial steels SA372J70, AISI4130 and X80 in high pressure hydrogen environment were investigated. Firstly, governing equations for hydrogen distribution and material damage evolution was established. Hydrogen enhanced localized flow softening effect was coupled within fracture strain dependency on stress triaxiality. Then, the numerical implementation and identification process of model parameters was described. Model parameters of the investigated steels were determined based on experiment results from literatures. Finally, with the calibrated model, fracture toughness reduction of the steels was predicted in a wide range of hydrogen pressure. The prediction results were compared with experimental results. Reasonable accuracy was reached. The proposed method is an attempt to reach balance between physical accurate prediction and engineering practicality. It is promising to provide a simplified numerical tool for the design and fit for service evaluation of hydrogen storage vessels.     

基于人工神经网络的智能化架空线路应变快速解调方法北大核心

为了提高智能化光纤复合架空线路态势感知的实时性,将人工神经网络方法应用于光纤沿线应变解调,确定了神经网络的结构。编程实现了基于洛伦兹模型的最小二乘谱拟合方法和神经网络方法,采用不同信噪比和布里渊频移的布里渊谱训练神经网络,将它们应用于某光纤复合架空线路沿线光纤应变的测量,从不同角度比较了两种方法的计算结果。计算结果表明,神经网络方法能有效获得光纤沿线的布里渊频移进而获得应变,具有与谱拟合方法相似的准确性,但应变解调时间仅约为谱拟合方法的1/20000。研究结果为提高智能光纤复合架空线路态势感知的实时性提供了参考。     

Numerical study of strain development in high-density polyethylene geomembrane liner system in landfills using a new constitutive model for municipal solid waste

Tensile strain development in high-density polyethylene (HDPE) geomembrane (GMB) liner systems in landfills was numerically investigated. A new constitutive model for municipal solid waste (MSW) that incorporates both mechanical creep and biodegradation was employed in the analyses. The MSW constitutive model is a Cam-Clay type of plasticity model and was implemented in the finite difference computer program FLAC?. The influence of the friction angle of the liner system interfaces, the biodegradation of MSW, and the MSW filling rate on tensile strains were investigated. Several design alternatives to reduce the maximum tensile strain under both short- and long-term waste settlement were evaluated. Results of the analyses indicate that landfill geometry, interface friction angles, and short- and long-term waste settlement are key factors in the development of tensile strains. The results show that long-term waste settlement can induce additional tensile strains after waste placement is complete. Using a HDPE GMB with a friction angle on its upper interface that is lower than the friction angle on the underlying interface, increasing the number of benches, and reducing the slope inclination are shown to mitigate the maximum tensile strain caused by waste placement and waste settlement.     

Improved electric-field-induced strain and strong photoluminescence properties in novel Er3+-modified 0.93Bi0.5Na0.5TiO3-0.07BaTiO3 multifunctional ceramics

Recently, the progress of electronic devices toward miniaturization has strongly promoted development of multifunctional materials possessing multiple desirable properties. In this study, we develop and fabricate 0.93Bi_0.5Na_0.5TiO₃-0.07BaTiO₃-xEr multifunctional ceramics which show simultaneously considerable electric-field-induced strain and bright green light emission properties. With the introduction of Er³⁺, the ceramics gradually transform from non-ergodic relaxor phase to ergodic relaxor phase which could reversibly transform to ferroelectric phase under the electric field. As a result, with improving Er³⁺ content, the shape of the polarization-electric field loops of the ceramics become pinched, and it is obvious that the negative strain disappears while the positive strain gradually increases and reaches a maximum value 0.46% at x = 1.2 mol%. Besides, After the ceramics are poled, the light emission peak are greatly enhanced attributed to the decreased crystal symmetry and increased domain size, and is the strongest at x = 1.2 mol%. These results indicate that 0.93Bi_0.5Na_0.5TiO₃-0.07BaTiO₃-xEr ceramics are good candidates for developing multifunctional optoelectronic devices.     

大直径埋地管道应力应变有限元分析与计算

利用通用分析软件ABAQUS，应用“生死单元” 技术，模拟了基坑开挖、填埋过程对Φ1 620 mm×20 mm大直径埋地管线应力应变的影响。通过对不同埋深管体应力应变的有限元分析，得出施加内压2.5 MPa，埋深8 m时，管体受到的等效应力最大（130 MPa），未超过材料的屈服强度，管体并未发生塑性变形，管体横向最大位移为2.47 mm。通过理论计算校核，埋深8 m时，管体水平方面最大变形量为12.5 mm，远小于标准规定的48.6 mm，管体径向稳定性可靠。     

Inhibition of stress corrosion cracking in 304 stainless steel through titanium ion implantation

The effects of titanium ion implantation on the stress corrosion cracking (SCC) behaviour of 304 austenitic stainless steel were studied. Slow strain rate tests (SSRTs) were conducted on 304 steel in air and in 5?wt-% NaCl solution. The microscopic effects of ion implantation were evaluated by Stopping and Range of Ions in Matter Procedures (SRIM). Fracture morphologies and microstructures were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The fracture surfaces illustrate that ion implantation significantly inhibits the corrosion pits that initiate SCC. A dense passive film, which inhibits SCC, was formed during the ion implantation process. SCC initiation was restrained due to the dense dislocation nets that were generated by titanium ion implantation.

Highlights

• Ion implantation inhibits SCC susceptibility.

• The lack of Cr at the grain boundary leads to the expansion of SCC along the grain boundary.

• Implantation-induced damage leads to high-density dislocations.

• The surface was amorphised due to high-density dislocations.

     

Structural optimization with an automatic mode identification method for tracking the local vibration mode

Traditional optimization methods, which take a specific order of modal frequency as the design constraint, could fail to obtain the desired solution because of modal substitution. An improved optimization model with continuous sizing variables is established to solve this problem, in which the minimum weight and a given local modal frequency are considered as the objective and the constraint. To capture accurately the expected mode of vibration, a local mode identification technique is proposed based on the strain energy ratio between the local area and the whole structure. With that scheme, an optimization system is developed, in which the local mode can be effectively identified and the constraint can be updated with it in the iteration process. Two numerical examples, of a reinforced plate and a satellite structure, are applied to illustrate the effectiveness and efficacy of the proposed method.     

不同距离应变片测定Ⅰ型动态应力强度因子对比试验研究

基于线弹性断裂力学理论，采用应变片法开展了冲击动荷载作用下的三点弯曲试验，探讨距扩展裂纹不同距离的应变片测定Ⅰ型应力强度因子的差异。当应变片与扩展裂纹成特定锐角和钝角时，采用与裂纹扩展速度和应变片的位置相关的二项式表征裂纹尖端附近应变场，并结合理论解析和试验实测的应变与裂纹扩展时间曲线，推导得到了应力强度因子计算公式。同时，采用动焦散线试验对比分析应变片法测定的动态应力强度因子值。结果表明，应变片在裂纹尖端附近合理区域内，测定的裂纹尖端动态应力强度因子值与动焦散线试验结果吻合较好;明确了不同距离对测定Ⅰ型裂纹应力强度因子的影响，随着应变片粘贴距离变大，测定的动态应力强度因子值与动焦散线法相差增大。研究结果为进一步应用应变片法研究岩石类材料的断裂性能提供了试验基础。     

Second- and third-order elastic constants of kesterite CZTS and its electronic and optical properties under various strain rates

In this paper, the continuum approach is used to calculate the second-order elastic constants and the third-order elastic constants of the kesterite CZTS semiconductor. In this approach, by applying the various deformation types to matter and using density functional theory the energy–strain curves are plotted and the corresponding elastic coefficients are extracted. In this paper, the effect of symmetrical strains on CZTS electronic and optical properties has been investigated. For kesterite CZTS, a bandgap of about 0.2 and 1.8 eV with revised Perdew?–Burke?–Ernerhof for solids functional and HSE06 approximation, respectively, ? is obtained. This semiconductor has been conductive in tensile strains and in return, increased its bandgap in compressive strain. In addition, its bandgap becomes indirect in the strains about ?9%. Also, the first peak in the imaginary section of the dielectric function has well conformity to experimental results and its changing process can show the changing process of optical bandgap under external strains such as temperature variations and substrate mismatch.