无相变合金淬火热应力演变机理的理论模型——（3）淬火热应力拓扑模型及形状影响热应力规律

建立了几何拓扑模型和热应力拓扑模型,从这2种拓扑模型的结构、形状和对称性、特别是多次对称轴之间的关系,深入分析了角端、边缘、表层、内部4种淬火模型以及淬火角端效应和动态薄膜效应之间的内在联系,并指出了各种具体的工业实际应用.淬火过程中,热力学拓扑模型的对称轴(特别是n次对称轴)将以变化的θ角围绕几何拓扑模型的对称轴(特别是n次对称轴)不停转动,θ的大小由几何拓扑模型和动态薄膜共同决定,θ=0°或θ很小时,是理想状态层状分布热应力,θ较大甚至接近90°时,发生淬火角端效应和淬火动态薄膜效应.并且热力学拓扑模型的对称轴(特别是n次对称轴)指向的表面出现拉应力,和该轴成垂直方向的表面出现压应力.     

7050铝合金零件淬火过程中温度场及热应力场的模拟研究

综合考虑了7050铝合金材料热物性参数与力学性能参数的非线性问题,借助有限元软件ABAQUS对7050铝合金法兰盘零件进行了淬火过程中温度场、热应力场的计算机数值模拟,得到其冷却曲线与热应力分布情况.结果表明:7050铝合金零件淬火过程中表层金属承受拉应力,心部金属承受压应力的空间分布特征,且无论是拉应力还是压应力都在淬火开始不久出现峰值,至冷却结束时整个零件的应力状态趋于平衡,应力降低至最小值.     

无相变合金淬火热应力演变机理的理论模型——（2）表层和内部淬火热应力模型及淬火动态薄膜效应

建立并深入分析了3种表层淬火热应力模型和2种内部淬火热应力模型及其实际应用。同时建立了不发生淬火角端效应时角端和边缘的二维和三维淬火模型及其实际应用。提出了淬火动态薄膜效应，按照有无动态薄膜效应归类分析了各种常见淬火介质淬火热应力的分布形态并深入讨论了淬火动态薄膜效应与淬火角端效应之间的联系与区别。     

空心圆柱件内孔的淬火应力

为了分析空心圆柱件淬火时内孔开裂的原因,通过二次开发在Abaqus软件平台上建立了空心圆柱件淬火时温度场、组织场和应力场的三场耦合模型。基于数值模拟对空心圆柱件淬火时的热应力及相变应力(组织应力)进行了分析,并对冷却介质换热系数对内孔淬火应力的影响进行了研究。结果表明：薄壁件在水淬后内壁表层及次表层的残余应力均为拉应力,厚壁件在经水淬后内壁和外壁表面残余应力均为压应力,内外壁的中间位置为拉应力;厚壁件内壁的最大拉应力在冷却过程中出现;引起薄壁件和厚壁件内壁开裂的原因是相变应力。通过分析空心件内孔淬火应力的影响因素并结合实际情况,提出了降低圆柱件内壁淬火应力的工艺方法。生产实践表明：基于数值模拟设计的淬火工艺未出现淬火开裂现象,并且材料的各项力学性能满足要求。     

5CrNiMo钢挤压模具淬火过程的数值模拟

借助ABAQUS有限元分析软件对几何形状复杂的5CrNiMo钢挤压模具淬火过程的温度场及热应力场进行数值模拟.计算综合考虑了非线性的材料热物性参数、力学性能参数、表面换热系数及相变潜热的影响.研究表明,淬火初期,工件表面与心部仅存在较小的温差,随淬火时间的延长,该温差不断增大,淬火约5s时,该温差达到最大值,此时表面温度虽已降低到192℃,但心部温度仍高达780℃,此后该温差不断减小,淬火约460s时,工件表面和心部温度趋于与介质相同的温度(20℃);淬火过程的热应力变化在工件内外表现为不同的特点,对于表面和心部节点,其主要表现为:表面先呈拉应力后呈压应力,心部先呈压应力后呈拉应力.     

6063铝合金在线淬火实验及有限元模拟

通过淬火试验获得了6063铝合金的在线淬火冷却曲线,结合数值方法获得该合金的在线淬火换热系数,运用ABAQUS有限元软件动态模拟了其在线淬火过程.结果表明:喷水淬火初始阶段,换热系数较小,随着淬火温度降低,换热系数逐渐增大至峰值约47 kW/(m2·℃),随后又逐渐减小;有限元模拟获得的冷却曲线与实测冷却曲线基本吻合;淬火时试样的温度分布符合一维传热特征,轴向应力呈“内压外拉”状态,且无论是拉应力还是压应力都在淬火开始不久后出现峰值.     

铝合金大型锻件淬火过程的有限元模拟

采用Deform V11有限元软件,计算了T形7N01铝合金锻件的表面综合换热系数,仿真模拟了锻件淬火过程中的温度场、应力场与形变位移变化规律,分析了温度与热应力对锻件淬火形变的影响与作用机制。结果表明,淬火初期因温度梯度(最大温差达225 ℃)与热应力巨大差异,锻件肋板一侧在淬火时间为10 s时产生了最大程度的弹性与塑性变形,远大于无肋一侧,弯曲曲率增大;淬火中期锻件主要发生弹性形变,厚度大的肋板一侧收缩变形加剧,曲率变小,50 s时锻件基本不再变形;淬火后期阶段热应力趋于零,锻件冷却产生微量弹性形变,淬火结束后,锻件整体产生趋向肋板一侧的塑性弯曲变形,曲率半径大于加热前。     

Al-Zn-Mg-Cu系高强铝合金厚板淬火过程数值模拟

采用Simufact有限元分析软件,对4000 mm×720 mm×285 mm尺寸的Al-Zn-Mg-Cu新型高强铝合金厚板淬火过程进行了模拟分析。结果表明,淬火过程中厚板表面和心部存在很大的温度梯度,同时各部分温降速率不断变化,淬火26 s时表面平均温降速率由10.43℃/s急降至小于0.01℃/s,而心部温降速率则是缓慢减小。厚板残余应力,淬火初期表现为外拉内压,淬火后期则为外压内拉。淬火后,厚板表面最大残余压应力分量约为-175 MPa,心部最大残余拉应力分量约为199 MPa。     

大型锻件水空交替淬火过程的数值模拟

建立了33N iCrMoV14-5钢淬火过程温度-组织-应力耦合的数学模型,用自主有限元软件模拟了淬火过程中锻件温度场、组织场、应力场的演化过程,对不同的淬火工艺进行了比较。模拟结果表明水冷-空冷交替的淬火工艺可改善锻件表面附近的淬火应力状态,同时获得足够的心部冷速。对锻件内部应力场的计算表明水空交替淬火中,相变对应力场变化的影响大于热应力。     

42CrMo钢输出法兰感应淬火的数值模拟及验证

基于电磁-热-组织-应力耦合模型,采用数值模拟研究了42CrMo钢输出法兰感应淬火过程中的温度、组织和应力的变化规律,同时采用硬化轮廓对比和硬度检测验证了模拟的可靠性。研究表明,在加热阶段,输出法兰圆弧过渡区的上、下尖角比中间位置先到达奥氏体化温度,感应区域温度到达材料居里点后加热效果逐渐减小;随着温度升高,法兰表面的组织由原始组织向奥氏体组织转变;法兰表面应力在加热阶段为压应力状态,加热开始阶段迅速增大,随着内部温度升高逐渐减小;在淬火阶段,温度迅速降低,表层奥氏体快速转变成马氏体,表层处应力经过短暂拉应力时刻,然后转变成压应力(轴向、径向和切向应力都为压应力),其中径向压应力最大,约为460 MPa。     

预拉伸对铝合金焊接残余应力和变形的影响

在预拉伸应力作用下，进行了厚度为4mm的5A05铝合金试板的焊接，焊后残余应力及变形的测定结果表明．预拉伸焊接法可有效减小铝合金薄板焊后的纵向残余应力、纵向挠曲变形和平面变形。在弹性应力范由内，随着预应力的增大，试板的残余应力峰值、纵向挠曲变形及平面变形均逐渐减小。分析认为，预拉伸应力部分抵消了焊接区热膨胀产生的压缩应力，从而减小了压缩塑性变形，进而减小了冷却时焊接区域的拉伸应力水平，相应地远离焊缝区域的压缩应力也随之减小。     

Experimental and Simulation Analysis of Thermal Shock with Rapid Heating Followed by Water Quenching for CuW70 Alloys

通过铜钨合金在快速加热后水冷的热冲击实验,研究了材料在热冲击后的力学性能变化。另外,应用有限元方法分析了合金在热冲击过程中的温度及热应力的分布及变化。结果表明,随着热冲击次数的增加,材料的强度减小而韧性明显增加;热冲击中,最大热应力出现在加热及冷却阶段的开始时刻,多次热冲击过程中,材料的内部和外部承受着在拉应力与压应力之间相互转换的交变载荷。     

数值计算模拟工艺参数对管道环焊缝残余应力的影响

以热——弹塑性理论为基础,建立了厚壁管环焊缝残余应力的二维轴对称有限元模型,利用ANSYS有限元程序分析了三种焊接工艺参数对管道环焊缝残余应力的影响,计算中考虑了材料热物理性能参数和力学性能参数的温度相关性.结果表明,管道内表面焊缝和近缝区的轴向和环向残余应力均为拉应力,而管道外表面焊缝和近缝区的轴向残余应力和环向残余应力均为压应力;接头内表面应力水平高于外表面;残余应力的最大值均位于距管道外表面一定距离处,其数值接近于材料的屈服应力;随着焊接热输入的增加,残余应力峰值变化不大,塑性变形区宽度增加.     

热模拟试验机试样热压缩数值分析

针对热模拟试验机(Gleeble 3500)热轧试样高温压缩试验的动态变形、材料内部应力、组织损伤、动态应变量及材料各部分塑性变形差异性等问题，利用Deform 3D软件数值仿真开展研究。结果表明：随着压缩的进行，试样表面积先减少后增加，约在5 s时表面积最小，下降率为4.1%，在8.4 s后剧烈增加，增加率为14.4%。在整个压缩阶段试样两端承受应力最大约为70 MPa。破坏性损伤Damage值为0.22，应变为1.43，顶部区域变形速率最大为1.19 mm/s。空冷和淬火冷却过程中，试样顶底边界面角部区域温度下降最快，高温区域变化趋势为由长方形向圆角长方形，再向椭圆形转变。     

7050铝合金残余应力冷变形消减工艺仿真研究

实测了7050铝合金热物性参数得到了高温应力-应变曲线及淬火过程温度变化曲线,构建了7050铝合金热处理和冷变形工艺仿真模型,分析了7050铝合金试块固溶淬火、冷压过程的应力变化.结果表明:残余应力累积主要产生在固溶淬火阶段,淬火后残余应力为外压内拉状态.随着淬火温度的降低,试块心部拉应力有所提高.单向压缩后,心部的三...     

Predicting Quenching and Cooling Stresses within HVOF Deposits

Due to the nature of the HVOF and other thermal spray processes, residual stress build up in thick deposits is a significant and limiting problem since it impedes the coating behavior in service. The residual stress-state that evolves in a deposit is largely dependent on the thermal conditions to which the substrate/coating system has been subjected, and is a combination of quenching stresses, peening stresses that develop in some cases in HVOF, both of which arise during deposition, and cooling stresses, postdeposition. It follows that precise control of these phenomena is essential, if a thick deposit or one with low levels of residual stress are to be thermally sprayed. This paper applies looks at analytical and finite element techniques used to predict quenching and cooling stresses within tungsten carbide-cobalt thermally sprayed deposits. The analysis investigates and predicts the quenching and cooling stresses using improved analytical and finite element analysis techniques by validating the models with experimental results such as X-ray diffraction and the hole drilling method. The result of this paper is a thermo-mechanical equation for quenching stress which includes the effects of misfit strain, the Poisson’s effect, variation of coating and substrate thicknesses, thermal expansion, and process temperature effects.     

Changes in the misfit stresses in an Al/SiCp metal matrix composite under plastic strain

Results are presented from neutron diffraction measurement of the strains in each phase, matrix and reinforcement, of a metal matrix composite bar before and after deformation beyond the elastic limit by four-point bending. The strains in each phase have been converted to stress. A stress separation technique was then applied, and the contributing mechanisms separated and identified. In this way the changes in the different contributions owing to plastic deformation have been determined. It is found that, initially, the average phase stresses can be explained in terms of a combination of essentially hydrostatic phase average thermal misfit stresses in the matrix (tension) and particles (compression) combined with a parabolic macrostress from quenching. After plastic bending the change in axial macrostress is as expected for that for a monolithic bar, but unexpectedly the misfit stresses had relaxed to approximately zero in both the tensile and compressive plastically strained regions of the bar.     

Thermal residual stresses and stress distributions under tensile and compressive loadings of short fiber reinforced metal matrix composites

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Gas Quenching during Age Hardening of the Aluminium Casting Alloy Al-7Si-0.3Mg

For quenching of age hardenable aluminium alloys today predominantly aqueous quenching media are used,which can lead due to the Leidenfrost phenomenon to a non-uniform cooling of the parts and thus to thermal stresses.Particularly at thin-walled or complex shaped parts local plastic deformations can occur by the uneven thermal stresses. In relation to the conventional quenching procedures in aqueous media, gas quenching exhibits a number of technological,ecological and economical advantages. In comparison to liquid quenching media, gas does not change its phase during quenching. Moreover, the cleaning problem of the parts can be avoided. The quenching intensity can be adjusted by the variable parameters gas pressure and gas speed as well as the kind of gas and thus can be adapted to the requirements of the alloy. By the higher uniformity and the better reproducibility, gas quenching offers a high potential to reduce distortion. The goal of these investigations is to clarify, if the cooling rate during gas quenching is sufficient to obtain the specific required strength after age hardening of the alloy Al-7Si-0.3Mg. For this purpose different tests in high-pressure gas quenching facilities, gas nozzle fields and water quenching baths were performed.