Prediction of crack growth following a single overload in aluminum alloy with sheet and plate microstructure

The fatigue crack growth behavior under constant amplitude and under single overload of 2024 aluminum alloy in sheet and plate product form has been investigated. Constant amplitude fatigue crack growth tests showed superior crack growth resistance of the plate attributed to a pronounced roughness induced crack closure as a result of the coarse and elongated grain structure. Crack growth tests with single overload showed that the retardation effect caused by the overload is not primarily influenced by roughness crack closure at the crack path. In this case, the sheet material with lower yield strength revealed a higher retardation effect than the plate material. The observed crack growth behavior has been simulated with the LTSM-F model, which accounts for retardation of crack growth after an overload due to material strain hardening at the crack front. Dissimilar strain hardening at the crack tip due to different yield strength for the sheet and plate has been considered by means of strength gradients inside the overload plastic zone. The analytical results confirmed the observed material crack growth trends.     

单轴取向p型半导体CuI薄膜的制备与表征

在室温下用反应沉淀制取了CuI粉体,用溶液生长法在玻璃载体上制备了单轴取向p型半导体CuI薄膜。用XRD、SEM对样品进行了分析,结果表明,CuI粉体为片状结构;晶体薄膜是(111)晶面沿玻璃平行生长的单轴取向马赛克CuI薄膜。阐明了单轴取向CuI薄膜形成的机理。     

Investigation of sheet resistance in thin-film mixed-conducting solid oxide fuel cell cathode test cells

Patterned and thin-film electrode experiments are effective in isolating or separating the complex charge and mass transport processes involved in the oxygen reduction reaction within and on the surface of a mixed-conducting solid oxide fuel cell cathode, making it possible to correlate electrochemical performance with electrode geometry, reaction pathway, and limiting steps. Very little information about either the impact of sheet resistance on global response or on effective design of current collector configuration to avoid sheet resistance has been reported to date, however. In this contribution, an empirical numerical model is presented to simulate sheet resistance under various material and catalytic parameters, current collector configurations, and other experimental factors in thin-film, mixed-conducting working electrodes. This model is used to provide general guidance for effective current collector placement by mapping in parameter space. In general, continuous crisscrossing metal lines, deposited through e.g. photolithography, provide the best intra-film current collection while small, regularly spaced discrete contacts, provided by e.g. a metal mesh, provide less efficient intra-film current collection. Most thin-film aspect ratios and current collector configurations can be accommodated without severe intra-film sheet resistance limitation provided the current collectors are spaced appropriately.     

Drawing,flanging and hemming of metallic thin sheets: A multi-step process

This study deals with the multi-step classical hemming process on samples with complex geometries and a pre-strain state linked to the forming of curved surface. The influence of taking the anisotropy and the Bauschinger effect into account on the roll-in and loads is studied. The design of a specific device was realised so as to compare the numerical results and the experimental values. The simulations show a certain relevance in the use of shell elements compared to solid elements despite their use restriction, and good correlation between the calculations and the tests. The roll-in differences and the level of stress reached are low at the end of pre-hemming and hemming, although a significant rotation of sections which are initially perpendicular to the mean fiber is observed during flanging.     

Effect of anisotropic yield functions on the accuracy of hole expansion simulations

The deformation behavior of 780 MPa grade dual-phase steel sheet subjected to hole expansion is investigated both experimentally and analytically to clarify the effect of the material model (anisotropic yield function) on the predictive accuracy of finite element analysis of hole expansion. Biaxial tensile tests of the material were conducted; contours of plastic work and the directions of plastic strain rates are precisely measured and are in good agreement with those predicted from the Yld2000-2d yield function with an exponent of 4 ( [Barlat et al., 2003] and [Yoon et al., 2004]). Finite element and experimental analyses on the hole expansion of the material were conducted. The Yld2000-2d yield function with an exponent of 4 provides closer agreement with the experimental results than other yield functions. Consequently, the anisotropic yield functions significantly affect the predictive accuracy of the deformation behavior of the steel sheet subjected to hole expansion, and the biaxial tensile test is effective for identification of the appropriate anisotropic yield function to be used for hole expansion simulation.     

Strength prediction of sheet to tube single sided resistance spot welding

Single-Sided Spot Welding (SSSW) procedure is considered as a feasible method to join hydroformed or closed section parts to others in vehicle productions. A ‘doughnut’ shaped or ring nugget can be formed between the two workpieces during this process. The strengths of conventional button spot welds can be determined by the attributes of weldments and many functions that link weld diameter, sheet thickness and material properties to weld strength have been established. For welds of sheet to tube joining, the strength prediction model is greatly different from that of conventional welds for the completely different nugget form. In this study, computer experiments were conduced using the concept of design of experiments (DOE) and the method of finite element used to simulate the tensile-shear tests. The stress and strain distribution contour clouds during tensile-shear process were analyzed and quantitative relationship models were established to link a weld’s geometric and material properties to its tensile-shear strength. The results can give a simple judgment whether a ring spot weld was good only by its appearance.     

热处理对14MnVTiRE钢4 mm薄板组织和力学性能的影响

14MnVTiRE钢[/%:0.10～0.15C、0.30～0.60Si、1.20～1.60Mn、0.03～0.09V、0.07～0.16Ti、0.10～0.15RE(加入量)]4 mm薄板的生产流程为180 t顶底复吹转炉-180 mm×1 260 mm连铸板坯-连轧-卷取工艺。在连铸时由结晶器喂φ2.5 mm RE丝。试验研究了950℃正火,950℃正火+690℃1～5 h回火对薄板组织和力学性能的影响。结果表明,正火后钢的组织为铁素体+细珠光体,在正火+690℃回火1～3 h钢中的珠光体片层碳化物发生球化,分布在晶界和晶粒内部,随回火时间进一步增加,碳化物呈点状和三角形,全部分布在晶界,材料的强度降低很大。14MnVTiRE钢薄板的最佳热处理工艺为950℃正火+690℃1～2 h回火,其屈服强度为510～610MPa,抗拉强度630～680 MPa,伸长率22%～25%。     

大轴重铁路货车车轴用新型LZ45CrV钢坯的开发

大冶特钢采用60tUHP EBT EAF-LF-VD-6.5t铸锭-850初轧开坯的工艺流程试制了大轴重车轴用260mm×260mm和280mm×280mm新型LZ45CrV钢坯(/%:0.43C、0.27Si、0.77Mn、0.007P、0.005S、0.55Cr、0.10V、0.10Mo)。通过电弧炉配加45%铁水和优质废钢,控制终点[C]≥0.15%,[P]≤0.005%,LF喂铝线,使Al控制在0.035%～0.045%,VD真空处理≥20min等工艺措施,LZ45CrV钢坯的氧含量为8.5×10^-6,非金属夹杂物≤1.0级,晶粒度7～8级,力学性能符合标准和设计要求。     

50 t EBT EAF-LF( VD) -CC流程生产G55SiMoVA轴承钢的工艺实践

石油钻具用轴承钢G55SiMoVA(/%:0.52~0.55C,0.90~1.10Si,0.30~0.50Mn,0.40~0.60Mo,0.20~0.30V,≤0.015P,≤0.015S)的工艺流程为废钢+60%~70%铁水-50 t UHP EBT EAF-60 t LF-VD-260 mm×300 mm连铸。通过采用电弧炉全程泡沫渣埋弧操作,EBT出钢合金化,控制LF二次精炼渣(/%:46~54CaO,10~16SiO₂,11~13Al₂O₃,4.5~7.0MgO)碱度3.2~4.5,SiC扩散脱氧和60~80 L/min流量氩气搅拌,VD 67 Pa真空状态下保持20 min,连铸全程保护浇铸,所生产G55SiMoVA轴承钢轧材中氧含量为9×10^-6~10×10^-6。     

Q345E低合金高强度钢Φ600 mm连铸圆坯的生产实践

Q345E钢(/%:0.14~0.17C、0.20~0.30Si、1.28~1.38Mn、≤0.011P、≤0.005S、0.015~0.030Al、0.032~0.045V)大圆坯的生产流程为65 t LD-LF-VD-Φ600 mm圆坯CC工艺。通过出钢时滑板挡渣,加入预熔合成渣(/%:40~50CaO、≤9SiO₂、30~40Al₂O₃~7MgO、8~10Al)、钢芯铝、脱氧剂和合金,控制拉速0.22 m/min,32 t中间包钢水过热度(25±5)℃,恒液面900 mm,全程保护浇铸和电磁搅拌等措施,试生产法兰用Q345E钢Φ600mm连铸圆坯。生产结果表明,铸坯表面无可见冷疤、鼓肚等缺陷,中心缩孔0.5级,中心疏松1.0级,碳偏析≤1.09,-50℃低温冲击功超过100 J,完全满足标准要求。