Failure Analysis of Motor Tire Bead Wires During Torsion Test

Torsion testing is used to determine the quality of steel wire used for motor tire beads in pneumatic tires. These steel wires must have good-tensile strength so that the tire bead can support the finished tire safely, and yet retain adequate ductility to deform easily around the forming wheel. The present paper highlights premature failure of bead wire which failed during torsion test. Torsion property is one of the important parameters of tire bead as it monitors both the metallurgical soundness and surface quality of a drawn wire. From the analysis, it has been concluded that probable reason for premature failure is due to strain aging (dynamic and static) caused by interstitial atoms which bounds the mobile dislocations resulting in increases yield strength and decreases bead formability. Moreover, the microstructural study indicates that failed specimen has misaligned and broken lamella of pearlite with globular cementite which creates the array of voids. These voids hinder the rotation of pearlite during torsion test thus leading to brittle fracture.     

基于 CMT 电弧增材的焊缝成形尺寸规律研究

目的研究焊接参数对焊缝成形尺寸的影响规律。方法基于冷金属过渡技术,采用正交试验方法得到在不同参数组合下焊缝熔宽、余高和第2层增高,通过多元线性回归拟合,建立了焊缝熔宽、余高和第2层增高与焊接参数之间的回归模型。结果影响焊缝熔宽和余高的主要焊接参数是焊接速度,影响焊缝第2层增高的主要焊接参数是送丝速度,而层间温度的变化对熔宽会有显著影响,但是对余高和第2层增高的影响不大,而且焊缝第2层的增高与余高在数值上存在较大的差异,对比预测值和试验值验证了回归模型的准确性。结论通过改变焊接速度可以引起熔宽和余高的显著变化,层间温度对余高和第2层增高不会造成很大影响。     

Experimental investigation on the effects of process parameters of GMAW and transient thermal analysis of AISI321 steel

Gas metal arc welding (GMAW) develops an arc by controlling the metal from the wire rod and the input process parameters. The deposited metal forms a weld bead and themechanical properties depend upon the quality of the weld bead. Proper control of the process parameters which affect the bead geometry, the microstructures of the weldments and the mechanical properties like hardness, is necessary. This experimental study aims at developing mathematical models for bead height (HB), bead width (WB) and bead penetration (PB) and investigating the effects of four process parameters
viz: welding voltage, welding speed, wire feed rate and gas flow rate on bead geometry, hardness and microstructure of AISI321 steel with 10 mm thickness. The transient thermal analysis shows temperature and residual stress distributions at different conduction and convection conditions.     

胎圈钢丝工字轮包纸机的设计与试验

针对手工包装胎圈钢丝工字轮劳动强度高、生产效率低的问题,设 计了国内首台胎圈钢丝工字轮包装机,并对胎圈钢丝工字轮包装机的关键机 构进行了分析和设计。包装过程中气相防锈纸易偏移,为此设计了防止包装 材料偏移的纠偏机构,从夹纸位置和放纸位置分析纠偏机构,并确定了其结 构设计和工作参数。试验结果表明,胎圈钢丝工字轮包装机的包装成功率为 98.9%,纸带褶皱率为 0.05%,包装速度为 30.4 个 /h;比较同一时段内机器 包装和手工包装的数量和质量,一台机器可替代企业 10~12 名工人。本包装 机为企业降低了生产成本,也为胎圈钢丝工字轮包装提供了新的方向。     

不同时效工艺对82B钢盘条性能的影响

用OM,SEI技术和万能材料试验机研究对比了82B钢轧制线材集卷后,自然时效0～30d（天）过程中的力学性能变化、宏观断口形貌以及微观断口韧窝形态的差异,并对自然时效与集卷后人工时效（在250℃或300℃加热、保温2h后缓慢冷却）后的力学性能进行了对比。结果表明：人工时效的力学性能约相当于15d自然时效的效果,从而提高了生产效率。     

On the mechanics of wire cutting of cheese

The wire cutting process is used in the food industry during the manufacture and testing of products. The cutting process involves fracture as well as large strain deformation and surface friction. This paper investigates the mechanics of the wire cutting process of cheese through a combination of experiments, theory and finite element simulations. The experiments revealed that there was secondary damage on the cut surface, thus a higher fracture energy would be consumed than the common assumption of a single crack propagation. The numerical simulations showed that there was a six-fold change in the strain rate when wire diameters of 0.25  to 2 mm are used. This strain rate effect was modelled through a modification of a previous theoretical analysis of the wire cutting process. The numerical models were also used to predict the cutting forces using two failure criteria: critical strain, which was applied to the initiation of cracking, and a cohesive zone model to simulate crack propagation. Both criteria showed reasonable success in predicting the cutting forces, particularly for cuts made with small wire diameters.     

Predicting of bead undercut defects in high-speed gas metal arc welding (GMAW)

In the gas metal arc welding (GMAW) process, when the welding speed reaches a certain threshold, there will be an onset of weld bead undercut defects which limit the further increase of the welding speed. Establishing a mathematical model for high-speed GMAW to predict the tendency of bead undercuts is of great significance to prevent such defects. Under the action of various forces, the transferred metal from filler wire to the weld pool, and the geometry and dimension of the pool itself decide if the bead undercut occurs or not. The previous model simplified the pool shape too much. In this paper, based on the actual weld pool geometry and dimension calculated from a numerical model, a hydrostatic model for liquid metal surface is used to study the onset of bead undercut defects in the high-speed welding process and the effects of different welding parameters on the bead undercut tendency.     

Predicting of bead undercut defects in high-speed gas metal arc welding (GMAW)

In the gas metal arc welding (GMAW) process, when the welding speed reaches a certain threshold, there will be an onset of weld bead undercut defects which limit the further increase of the welding speed. Establishing a mathematical model for high-speedGMAWto predict the tendency of bead undercuts is of great significance to prevent such defects. Under the action of various forces, the transferred metal from filler wire to the weld pool, and the geometry and dimension of the pool itself decide if the bead undercut occurs or not. The previous model simplified the pool shape too much. In this paper, based on the actual weld pool geometry and dimension calculated from a numerical model, a hydrostatic model for liquid metal surface is used to study the onset of bead undercut defects in the high-speed welding process and the effects of different welding parameters on the bead undercut tendency.     

Strain gradient theory based on a new framework of non-local model

A new framework of non-local model for the strain energy density is proposed in this paper. The global strain energy density of the representative volume element is treated as a non-local variable and can be obtained through a special integral of the local strain energy density. The local strain energy density is assumed to be dependent on both the strain and the rotation-gradient. As a result of the non-local model, a new strain gradient theory is derived directly, in which the first and second strain gradients, as well as the triadic and tetradic stress, are introduced in the context of work conjugate. For power law hardening materials, size effects in thin metallic wire torsion and ultra-thin cantilever beam bend are investigated. It is found that the result predicted by the theoretical model is well consistent with the experimental data for the thin wire torsion. On the other hand, the calculation result for the micro-cantilever beam bend clearly shows the size effect.     

Effects of temperature distribution on plasticity in laser dieless drawing

Temperature measurement based on grey body radiation spectrum is used to determine the temperature profile of hot wires in the deformation region in laser dieless wire drawing, with spatial resolution down to a few micrometers. The Voce parameters characterizing the high temperature plastic flow behavior of the wires are calculated using the temperature and diameter profiles of the wires in the deformation region. These parameters are determined for as-drawn and annealed pure nickel wires of 500 m diameter. Recrystallization and grain growth during the drawing process are studied. The effects of temperature, grain size and precursor wire diameter on wire drawability and strain rate are analyzed. The measured temperature and diameter profiles agree well with theoretical results. Grain growth increases rapidly with increasing temperature after recrystallization, and the grain size follows the thermal activation law. The effective activation energy increases for larger wire diameter. Surface morphology of the drawn wires and strain rate calculation show that dislocation motion is the dominant deformation mechanism.     

Investigating effects of resistance wire heating on AISI 1023 weldment characteristics during ASAW

In this article, effects of advanced submerged arc welding process parameters on weld bead geometry have been investigated. A novel water-cooled torch has been developed which allow a use of higher preheat current values for a continuous advanced submerged arc welding (ASAW) operation. Weld beads have been deposited on AISI 1023 steel plates by varying open circuit voltage, wire feed rate, welding speed, nozzle to plate distance, and preheat current as per central composite design. The relationships between welding parameters and weldment characteristics namely bead width, penetration, reinforcement, and dilution have been developed using multiple linear regression. The effects of individual process parameters and their interactions on response parameters were examined. Finally, single and multiobjective optimization of process parameters were performed using desirability approach and Jaya algorithm. The results reveal that a smaller bead width and lower dilution can be achieved with the developed torch by allowing the use of higher preheat current values.     

Effect of rolling speed on the occurrence of strain aging during and after warm rolling of a low-carbon steel

In this study, effect of rolling speed on strain aging phenomena in warm rolling of a carbon steel has been investigated. For this purpose, by using a mathematical model and predicting temperature and strain rate fields, the possibility of occurrence of dynamic strain aging during the warm rolling was first evaluated. In the next stage, warm-rolled samples were aged up to 11 months at room temperature for studying the kinetics of static strain aging, while mechanical tests as well as microstructural evolutions have been performed to determine the effect of strain aging on material behavior. The results indicate that dynamic strain aging may not occur for the employed rolling program; however, static strain aging takes place after warm rolling leading to changes in the mechanical behavior of the warm-deformed samples. In addition, by increasing rolling speed, the aging time required to achieve the maximum hardness increases.     

Characterisation of quasi‐stationary temperature fields in laser welding by infrared thermography

In this work, high‐speed thermography is shown to effectively capture quasi‐stationary temperature fields during the laser welding of steel plates. This capability is demonstrated for two cases, with one involving the addition of a ferritic‐bainitic filler wire, and the other involving the addition of a low‐transformation‐temperature (LTT) filler wire. The same welding parameters are used in each case, but the temperature fields differ, with the spacing between isotherms being greater in the case where the low‐transformation‐temperature filler material is added. This observation is consistent with the differences in the extent of the heat‐affected zone in each sample, and the shape of the weld pool ripples on the weld bead surfaces. The characterization of temperature fields in this way can greatly assist in the development of novel methods for reducing residual stresses, such as the application of low‐transformation‐temperature filler materials through partial‐metallurgical injection (PMI). This technique reduces or eliminates tensile residual stresses by controlling the temperature fields so that phase transformations take place at the optimum times, and success can only be guaranteed through precise knowledge of the temperature fields in the vicinity of the welding heat source in real time.     

Effect of Welding Parameters on Dilution and Weld Bead Geometry in Cladding

The effect of pulsed gas metal arc welding （GMAW） variables on the dilution and weld bead geometry in cladding X65 pipeline steel with 316L stainless steel was studied. Using a full factorial method, a series of experiments were carried out to know the effect of wire feed rate, welding speed, distance between gas nozzle and plate, and the vertical angle of welding on dilution and weld bead geometry. The findings indicate that the dilution of weld metal and its dimension i.e. width, height and depth increase with the feed rate, but the contact angle of the bead decreases first and then increases. Meantime, welding speed has an opposite effect except for dilution. There is an interaction effect between welding parameters at the contact angle. The results also show forehand welding or decreasing electrode extension decrease the angle of contact. Finally, a mathematical model is contrived to highlight the relationship between welding variables with dilution and weld bead geometry.     

Pass schedule of wire drawing process to prevent delamination for high strength steel cord wire

The high-speed drawing of high carbon content steel wires is usually conducted at room temperature employing a number of passes or reductions through several dies. In the multipass drawing process, the temperature rise at each pass affects the mechanical properties of the final product (such as its bending and torsion properties, and its tensile strength). This temperature rise during deformation encourages delamination in the wire, which has a deleterious influence on the torsional properties and durability of the wire. In this study, we investigated the delamination of wires using torsion tests and evaluated the wire temperature during drawing. Our data shows that one of the main reasons for delamination was an excessive rise in wire temperature. Based on our experimental results, in order to prevent delamination due to an excessive rise in wire temperature, a new isothermal pass schedule that could control the wire temperature was designed. The pass redesign for the conventional high carbon (0.75 wt%C) steel cord wire drawing process with delamination was carried out by using the isothermal pass schedule to control the wire temperature. In order to verify the effectiveness of the proposed method, wire drawing and torsion test were conducted. From the results of experiments, it was possible to produce high carbon steel cord wire without delamination.     

Characterization of Austenite Dynamic Recrystallization under Different Z Parameters in a Microalloyed Steel

A low carbon Nb-Ti microalloyed steel was subjected to hot torsion testing over the temperature range 850-1100℃ and strain rates 0.01-1s-1 to study the influence of deformation conditions on the dynamic recrystallization characteristics of austenite.The results show that dynamic recrystallization occurs more easily with the decrease of strain rate and the increase of deformation temperature.The complete dynamically recrystallized grain size as a function of Zener-Hollomon parameter was established.It was found that dynamically recrystallized grain sizes decrease with increasing strain rate and decreasing deformation temperature.The effect of microalloying elements on peak strain was investigated and the solute drag corrected peak strain was determined.Also,the dynamic recrystallization map of austenite was obtained by using recrystallization critical parameters.     

基于焊道尺寸控制的电弧增材成形高氮奥氏体不锈钢与316L不锈钢交织结构EI北大核心CSCD

采用高氮奥氏体钢与316L不锈钢丝材,对高氮奥氏体不锈钢熔覆焊道、单道多层、单层多道表面成形特性进行分析,筛选适宜的工艺参数。通过控制两种材料焊道尺寸,获得最适用于成形异材交织结构的工艺参数。利用不同道间距实验得到异材焊道的最佳道间距,并采用合理路径,制备电弧增材成形交织结构。结果表明:工艺参数的变化对高氮奥氏体不锈钢焊道表面成形特性影响极大,易出现气孔;提出异材焊道几何尺寸、截面面积匹配误差法,获得最佳工艺参数:其中高氮奥氏体钢丝材的送丝速率为5.7 m/min,316L不锈钢丝材的送丝速率为5.6 m/min,焊接速率均为0.6 m/min。通过降低起弧次数,采用闭合路径,提高了异材交织结构成形精度,减少了后处理加工。     

爆炸驱动多层球形破片初速场分析

为准确计算多层球形破片在爆炸驱动下的初速场,通过对装药结构的等效分析,基于Gurney假定和相邻层颗粒之间力和力的波动量等概率传递假定,忽略排列方式引起的孔隙率变化,应用动量和能量守恒建立了破片初速场的理论计算模型。该模型反映了炸药参数和破片的密度、层数和直径等因素对破片初速的影响;针对典型的爆炸驱动前向多层破片模型,用LS-DYNA3D非线性有限元程序对多层钨球破片的爆炸驱动过程进行数值模拟,开展了相关验证试验并分析了理论计算值与试验误差产生的原因,分析讨论了不同球形破片直径和不同破片层数下破片初速的变化情况。结果表明:理论计算值与数值模拟及试验结果吻合较好;随着相同直径破片层数的增大,破片初速减小,相邻层间破片的速度差值更大;层数相同时,随着破片直径的减小,破片初速增大,但相邻层数破片的速度差值更小。     

Single Pass Laser-Arc Hybrid Welding of Maraging Steel Thick Sections

Maraging steel 250 grade plates of 10 mm thickness were welded in single pass using a laser-arc hybrid welding (LHW) setup comprising 3.5 kW CO₂ laser and synergic pulse metal inert gas (MIG) welding power source at a welding speed of 1 m/min. The influence of single-pass welding on the bead characteristics, microstructure, and mechanical properties was investigated. The size and volume fraction of reverted austenite was effectively reduced in the fusion zone. Moreover, the width of the heat-affected zones (HAZ) was reduced and the microhardness results did not show significant softening in the HAZ after post weld aging. Tensile testing of the welds in transverse direction showed 97.3% weld efficiency. The fusion zone exhibited K_Ic fracture toughness of 77.4 MPa√m which was affected by the distribution pattern of reverted austenite. The study vividly brings out the process advantages of LHW for accomplishing thick section welds of maraging steel in single pass with narrow groove and lesser filler wire consumption.     

An Analysis of the Factors Influencing the Data Derived from a Plug Type Three-Dimensional Strain Rosette under Compression and Torsion

Abstract:  The embedding of three-dimensional strain rosettes embedded into epoxy models provides an experimental technique for analysing complex structures; however, this technique has been known to produce data that were difficult to explain in terms of their physical significance. To gain a greater insight into the behaviour of a three-dimensional strain rosette used in this way, a three-dimensional strain rosette was embedded into each of two separate prismatic bars of square cross-section and subjected to fundamental tests of compression and torsion in standard commercial testing machines. In initial tests on a bar containing a three-dimensional strain rosette (Bar A) the data derived from the individual gauges sometimes departed from the theoretical values by more that 30  μ e. After critical evaluation of the procedures used for making and testing Bar A, further tests were carried out on Bar B, which led to a reduction in the difference between theoretical and experimental data to 14  μ e, acceptable for most practical purposes. The use of square plugs containing three-dimensional strain rosettes which are embedded into square cavities in the model, and the measurement of the actual direction cosines of the gauges on the square plug prior to embedment is a distinct advantage over the use of cylindrical plugs. In addition, the use of testing machines with a fixed base as opposed to a floating lower platen is recommended.