Analysis of the Mechanical Properties of an Arc Sprayed WC-FeCSiMn Coating: Compression, Bending, and Tension Behavior

This paper is concerned with the elastic and plastic forming behavior of arc sprayed WC-FeCSiMn coatings. The mechanical properties were investigated by indentation, bending, and tensile tests. These were performed on coated mild steel substrates as well as spark eroded and ground freestanding coatings with different geometries. The results of the indentation, bending, and tensile tests were evaluated concerning the coating microstructure, element, and pore distribution, as well as the local microhardness. The critical role of pores and inhomogeneities within the sprayed coating was examined in detail. Micro- and macrocracking were investigated by scanning electron microscopy after the indentation and tensile tests. It was figured out that the WC-FeCSiMn coating featured a distinctive brittle behavior. During the bending and tension tests, brittle forced fracture of the layer appeared almost without plastic deformations. A significant difference was determined between the compression and tensile performance of the coating. For instance, the Young??s modulus for compression strains was measured to be approximately 60% higher than the tension case.     

Square cup deep drawing and 2D-draw bending analysis of Hadfield steel

Hadfield steel is the dominant material in the production of bullet proof steel helmet for military uses. The conventional bullet proof steel helmets are extensively fabricated by cold forming (deep drawing) 1.2 mm Hadfield steel sheets at room temperature. This paper presents the experimental analysis of the square cup deep drawing and 2D-draw bending of Hadfield steel as a continuation of an international bench mark research program organized by NUMISHEET'93 organising committee in Japan. The draw-in values of the flange have been determined for various punch travels in the square cup operation. The principal strains were evaluated in three directions from grid measurments for those punch travels. Springback values and sidewall curls were also described in 2D-draw bending operation. The experimental results were compared with that of ones in mild steel.     

Mössbauer analysis of the magnetic structure of a high-carbon austenitic steel upon deformation and under pressure

A large plastic deformation of Hadfield steel (frictional action, shear under pressure, filing, and rolling) leads to the growth of an internal effective field at ⁵⁷Fe nuclei, magnetic-degeneracy removal in the spectra, and delay of the paraprocess up to room temperature. In the Mössbauer spectrum of the 120G13 Hadfield steel, the reversible formation of a hyperfine structure, which is supposedly connected with magnetic ordering, has been detected in situ upon quasi-hydrostatic compression to 26 GPa. The observed growth of magnetic characteristics upon deformation and under high pressure is explained by the deformation-induced redistribution of carbon with the formation of short-range ordering of oxygen and manganese.     

Transferability of critical condition for ductile cracking in bent small scale specimen to evaluation of critical internal pressure for ductile cracking in axially notched linepipe

Abstract

For two types of API 5L X65 linepipes, the critical conditions for ductile cracking of the linepipe steel and their applicability to the evaluation of the ductile cracking of an axially notched linepipe were investigated. Static three point bending tests and finite element (FE) analyses for a Charpy V notch specimen were conducted to evaluate the critical conditions for ductile cracking from the notch tip. At the position of ductile cracking for the Charpy specimen, the calculated stress triaxiality was almost constant for both linepipe steels; however, the equivalent plastic strain for each linepipe steel was different. Hydrostatic burst tests were then conducted for internally patched linepipes with an axial through wall notch. The results of FE analyses for the hydrostatic burst tests indicated that the maximum equivalent plastic strain value within the wall thickness was almost the same as that obtained from the three point bending test in the Charpy V notch specimen. It was therefore ascertained that the critical conditions for ductile cracking of linepipes with an actual notch can be predicted from the results of a small scale test and FE analysis, which are used to evaluate the relationship between the stress triaxiality and the equivalent plastic strain.     

Measurements of anisotropic yielding,bauschinger and transient behavior of automotive dual-phase steel sheets

In order to present better prediction capability in computational analysis, mechanical properties of the dualphase high strength steel have been characterized especially for anisotropy as well as the Bauschinger and transient behavior. As for the anisotropy, the non-quadratic anisotropic yield function Yld2000-2d has been utilized and its material parameters have been obtained using the uni-axial tension tests as well as the hydraulic bulge test. To measure the hardening behavior including the Bauschinger and transient behavior, a newly developed test method has been applied for the uni-axial tension/compression and compression/tension tests, in which solid blocks along the both sides of the sheet specimen prevent buckling. From the tension/compression curves, the equations to describe isotropic and kinematic hardening behavior have been obtained. The modified Chaboche model has been confirmed to well represent the hardening behavior including the Bauschinger and transient behavior.     

Strain hardening upon twinning of $$ [\bar 111], [\bar 144]$$ , and [011] single crystals of hadfield steel

Transmission electron microscopy and X-ray diffraction have been used to experimentally study the mechanism of deformation of Hadfield steel single crystals oriented for tension along $ [\bar 111], [\bar 144]$ [\bar 111], [\bar 144] , and [011] directions. It has been established that at T = 23 ° C starting from the early degrees of deformation (ɛ > 0.5%) the process of plastic flow in single crystals of these orientations is connected with the development of predominantly mechanical twinning. The influence of the number of operative shear systems on the rate of strain hardening has been shown.     

Ladle-treated high manganese steel reinforced by Cr7C3 phase

This research programme was designed to study the effect of chromium addition on the characteristic properties of Hadfield steel that has been produced by using the ladle treatment process. Chromium-containing ladle-treated Hadfield steel and chromium-free ladle-treated Hadfield steel have been produced, comparing with the Hadfield steel that has been produced by the conventional process. It has been found that chromium addition has a significant effect on the characteristic properties of the ladle-treated Hadfield steel. For instance, wear abrasion resistance was enhanced approximately five times much higher than conventional Hadfield steel. Moreover, an industrial trial indicates that chromium-containing ladle-treated Hadfield steel has significant benefits from the perspective of performance, and production cost as well.     

预应变状态对J55油套管钢在长庆油田地下洛河水中腐蚀电化学性能的影响

利用电化学阻抗谱（EIS）和光电流技术研究了拉伸、压缩及弯曲三种状态下J55油套管钢在长庆油田洛河水中所成钝化膜电化学性能及光电特性。结果表明：随着拉应力的增加,传递电阻R₁、膜电阻R₂及扩散电阻减小,表明拉应力增加可使钝化膜对基体耐腐蚀的保护作用减弱;随着压应力和弯曲应力的增加,传递电阻R₁、膜电阻R₂及扩散电阻增加,说明在压、弯曲应力状态下钝化膜对基体的保护作用增强。Mott-Schottky曲线测试结果发现,拉应变程度增加,M-S曲线直线部分的斜率减小,说明钝化膜内的施主密度增加;而随着压、弯曲应力增加,M-S曲线直线部分的斜率增大,表明膜内的施主密度减小。光电流测试表明,光电流随着拉应变程度的增加而减小,随压缩和弯曲应变程度的增加而增大。     

An approach to evaluation of sheet bending force under successive multiaxial stress condition

A new bending under tension test is presented in this paper. This method tries to evaluate bending forces in sheet under successive multiaxial stress condition. This test is carried out in only one step with a pinned cylinder over a material that has been previously deformed to pure shear condition. Due to that, the bending process is made under higher back tension forces than the ones involved in the common methods previously studied in the literature. This entails high pressure values in the sheet-bending tool contact that affects the corresponding friction process. Material is strongly strengthened as a consequence of the deformation practiced in it, and as a result of that, bending forces have higher values if compared with the ones considered in traditional assays. Then, in order to reproduce die radius conditions in deep drawing processes, this test establishes more real results than BUT tests commonly used. We have tried out electrogalvanized DDQ steel as an application of the test. Moreover, apparent pressure in bending tool has been determined by direct measures, that has been added to the traditional methods. Taking into account the apparent pressure values, friction has been evaluated in bending tool and finally the bending force has been obtained from the experimental data. Three bending angles and three tool radii have been experimented and their influence has been evaluated. It has been proved that bending force depends on bending angle to a great extent. Finally, we have shown that die radius has a minor effect on the bending force.     

The Bauschinger effect in the supercooled austenite of SAE 52100 steel

During the heat treatment and the welding of steel components, the interactions between the thermal and phase transformation strains result in cyclic loading of the component, which often results in plastic deformation. Although this has long been a well-known fact, the cyclic hardening behavior of supercooled austenite was not investigated up to now. In this study, tension–compression tests were performed on the supercooled austenite of SAE 52100 ball bearing steel at several temperatures using Gleeble3500® thermomechanical testing machine. The results were compared with conventional hardening models used in heat treatment and welding simulation. The results indicate that the metastable austenite exhibits a complicated cyclic hardening behavior that can only be partially reproduced by commercial simulation software. In the outlook, it is concluded that more complicated cyclic hardening models should be implemented for better prediction of distortion and residual stresses after heat treatment or welding.     

Discrete dislocation plasticity analysis of single crystalline thin beam under combined cyclic tension and bending

The cyclic plastic response of a single crystalline thin beam subject to combined cyclic tension and bending is analyzed using two-dimensional discrete dislocation plasticity. In this contribution, special attention is paid to the difference in the inherent mechanism of the size effect for different cyclic loads. Results show that the cyclic plastic response has a strong size effect for both cyclic pure tension–compression and pure bending. However, the inherent mechanisms are different. The dislocation starvation mechanism dominates the cyclic tension–compression while the geometrically necessary dislocation dominates the cyclic pure bending. When the combined cyclic tension and bending are applied to the thin beam, the cyclic moment–rotation response shows strong size effect while the stress–strain response shows weak or even no size effect. In addition, it is also found that the cyclic loading paths have considerable influences on the shape of the cyclic stress–strain loops.     

Influence of Tension-Compression Asymmetry on the Mechanical Behavior of AZ31B Magnesium Alloy Sheets in Bending

Magnesium alloys are promising materials for lightweight design in the automotive industry due to their high strength-to-mass ratio. This study aims to study the influence of tension-compression asymmetry on the radius of curvature and energy absorption capacity of AZ31B-O magnesium alloy sheets in bending. The mechanical properties were characterized using tension, compression, and three-point bending tests. The material exhibits significant tension-compression asymmetry in terms of strength and strain hardening rate due to extension twinning in compression. The compressive yield strength is much lower than the tensile yield strength, while the strain hardening rate is much higher in compression. Furthermore, the tension-compression asymmetry in terms of r value (Lankford value) was also observed. The r value in tension is much higher than that in compression. The bending results indicate that the AZ31B-O sheet can outperform steel and aluminum sheets in terms of specific energy absorption in bending mainly due to its low density. In addition, the AZ31B-O sheet was deformed with a larger radius of curvature than the steel and aluminum sheets, which brings a benefit to energy absorption capacity. Finally, finite element simulation for three-point bending was performed using LS-DYNA and the results confirmed that the larger radius of curvature of a magnesium specimen is mainly attributed to the high strain hardening rate in compression.     

基于有限元分析的摩擦系数测定

在塑性体积成形有限元模拟中,摩擦模型和摩擦系数的确定是一个关键问题.本文采用圆环镦粗法研究体积成形中摩擦系数的确定.利用有限元分析确定一组摩擦系数标定曲线,用圆环镦粗试验确定圆环内径变化率百分比与圆环高度压缩百分比关系曲线.通过曲线对比得到模具材料和成形材料之间的摩擦系数.针对6A02CZ材料在钢模具中体积成形时6A02CZ材料与钢之间的摩擦系数进行确定,6A02CS材料在无润滑剂和润滑油做润滑剂两种情况下的摩擦系数分别为0.325和0.3.研究表明,采用有限元方法和圆环镦粗试验相结合的方法更适合塑性体积成形中的有限元分析.     

AZ31B镁合金板材折弯过程中性层偏移规律研究

有效预测和评估板材变形程度对折弯成形工艺和产品精度控制有着现实的指导意义,且中性层偏移是衡量折弯板材拉压区域不均匀变形程度的重要参数。依据塑性变形理论中微元体应力平衡条件,基于能够体现镁合金拉压不对称性的Yoon2014屈服准则,得到了AZ31B镁合金板材折弯过程中中性层偏移量计算模型,并辅以有限元模拟和相应实验对中性层偏移模型进行验证。结果表明：所建立模型能够对镁板中性层偏移现象进行可靠预测,镁板在折弯过程中,受拉压不对称性的影响,中性层向拉伸侧偏移;折弯后角度越小,中性层偏移量越大,在折弯角度至90°,压下量为40～47 mm之间时的中性层偏移程度最明显。     

Reverse effect of tensile force on sidewall curl for materials with tensile/compressive strength difference

Sidewall curl occurring by the removal of tool surfaces after forming is one adverse phenomenon that should be effectively reduced in sheet metal forming operations. Among several process parameters controlling sidewall curl, a constraint tensile force is widely used along with attainable formability by introducing blank holder and drawbead. The classic but common knowledge is that sidewall curl is suppressed for conventional sheet metals as the constraint tensile force increases. Interestingly, however, for magnesium alloy sheets that have unusual asymmetry in tension and compression it has been recently reported that springback increases as the tensile force increases within a specific range of tension. The major deformation in the sidewall usually consists of bending and unbending under tensile force. Therefore, this unique stress-strain response of sheet materials with strength-differential, including magnesium alloys, should be considered for an accurate estimation of sidewall curl. In the present study, a semi-analytical bending/unbending theory incorporating characteristic constitutive behavior of magnesium alloys was developed to evaluate the moment-curvature relationship for various levels of constraint tensile forces. The present analysis proved that the reverse effect of constraint tensile force on sidewall curl was caused by the lower resistance to plastic yielding in compression with proper combination of applied tensile force.     

On the role of residual internal stresses and dislocations on Barkhausen noise in plastically deformed steel

The dependence of Barkhausen noise on elastic and plastic deformations, achieved in tension and in compression, has been investigated both in Armco iron and a low carbon steel. These materials exhibit quite different behaviours, especially with regard to the effect of plastic deformation: a tensile plastic deformation (>1%) induces a marked increase in Barkhausen noise for Armco iron while it induces a steep decrease in the low carbon steel. The comparison between the tensile and compressive behaviours, as well as between the elastic and plastic regimes of deformation enables us to attribute these effects to two underlying mechanisms, i.e. effect of residual internal stresses through magneto-elastic coupling and dislocation–domain wall interaction. In Armco iron, the latter mechanism seems to have the strongest influence on the Barkhausen noise, while in the low carbon steel the influence of residual internal stresses prevails.     

DEFORMAION AND WORK HARDENING OF HADFIELD MANGANESE STEEL

高锰钢的加工硬化主要来自两个方面:一是大量的孪晶变形使全位错和不全位错在共格的孪晶界面上运动受阻,一是变形过程中产生大量Mn-C原子对或MV-CC(锰-空位碳-碳)原子团,造成强烈的不对称畸变。高锰钢变形时,滑移不断调整孪晶变形,产生应力弛豫,从而使其既具有高的硬化率又有良好塑性。     

铜基非晶合金板弯曲塑性及剪切带间距的研究

制备了一种压缩断裂塑性应变接近2％的铜基块状非晶板材,并利用三点弯曲实验进行了其弯曲塑性、剪切带间距与试样厚度关系的研究．结果表明：非晶合金的弯曲断裂塑性应变明显依赖于试样厚度,即弯曲断裂塑性应变随试样厚度增加呈指数衰减关系减少;弯曲时剪切带间距随试样厚度增加而线性增加;剪切带间距与试样厚度的比值对于同一非晶合金为恒定值,但随非晶合金种类的不同而变化,与非晶合金的塑性变形能力有关．     

DEFORMATION AND WORK HARDENING OF HADFIELD MANGANESE STEEL

The work hardening of Hadfield manganese steel arises mainly form two causes;1)a largeamount of twinning makes perfect dislocations or Shockley dislocations to be blocked at thecoherent twin boundaries.2)the deformation leads to strong unsymmetrical distortion due tothe occurrence of a large number gf Mn-C pairs or Mn-vacancy carbon-carbon cluster.Ithas been demonstrated by TEM observation and internal friction tests.As deformation pro-ceeds,the slip constantly accomodates twinning shear giving rise to stress relaxation.Thus,the Hadfield steel exhibits both rapid work hardening and good ductility.     

Analysis of the interpretation of yielding and strengthening behavior in small-size samples

In recent literature related to mechanical testing of small-volume metal specimens, plastic strain bursts during apparent elastic loading have been reported for materials commonly known to exhibit smooth yielding. Interpretation of the observed plastic yielding effects in these tests have ignored a significant part of the actual experimental findings, and produced conclusions regarding dislocation structure that these tests do not unequivocally support. It is pointed out that the heterogeneity of dislocation debris left in the microstructure does not clearly represent deformation resistance, nor give a clear indication of strain within the specimen. The measured high rate of strain hardening and stability of plastic flow in the small-volume specimens are dependent on stress-state, and are shown to be not correlated with dislocation debris or dislocation-starvation concepts; rather the reason for the observed strengthening is related to the resistance to slip propagation through the specimen surface to form surface steps, viewed as an atomic-scale shear fracture process, elaborated in a companion paper. In a compression test the surface is closed under high compressive stress, thus repeatedly blocking the process, but in a tension test the surface separates more easily, causing loss of plastic stability.