单曲率焊接多面壳体液压胀形过程研究

球形容器无模胀形工艺是对传统球形容器制造工艺的重大变革。本研究针对该工艺在应用于建造大型球形容器时所遇到的困难,首次提出采用桔瓣式单曲率多面壳体作为胀形前的多面壳体,给出了桔瓣式单曲率多面壳体结构设计方法和计算公式,试验研究了该种多面壳体胀形建造的球形容器的不圆度、角度变形和壁厚分布,利用非线性有限元程序对桔瓣式单曲率多面壳体的胀形成球过程进行了数值模拟,给出了该类多面壳体胀形时的形状变化和壳体应力分布规律。 首次提出了多面壳体等面积球面的概念和等面积趋球原理,并用该原理判断了多面壳体无模胀形时其上各点的移动方向和起皱发生部位,估算了胀形后所得球形容器的直径。还首次对各种多面壳体起皱机理进行了研究,给出了起皱原因,起皱部位判据,以及减皱、消皱的措施。 采用桔瓣式单曲率多面壳体液压胀形方法成功地建造了20多台球形容器,其中包括直径8000mm,壁厚8mm的球形水塔和直径7100mm,壁厚24mm的液化石油气储罐(已安全运行两年多)。在这些球形容器的制造过程中,无一例胀裂事故发生。工程应用结果表明,桔瓣式单曲率多面壳体无模胀形适用于大型球形容器的建造。     

单曲率多面壳体高温胀形制造球形容器工艺

提出单曲率多面壳体高温胀形制造球形容器工艺的基本思想。对内切球面直径为μ420mm,壁厚为1．2mm的低碳钢单曲率多面壳体加热到胀形温度时的温度场进行了测量,对壳体的高温胀形成形过程进行了数值模拟。壳体加热结果表明,其温度场的最大温差值为80℃,数值模拟结果表明,在壳体壁的最高温度与最低温度相差达80℃时,单曲率多面壳体可以成形为球形容器。     

低碳钢薄壁焊管液压胀形行为

为了研究焊管液压胀形过程的变形行为,在管材胀形性能测试系统上进行了不同长径比条件下低碳钢(STKM11A)薄壁焊管的胀形实验,获得了焊管的壁厚分布规律、胀形区轮廓形状、极限膨胀率和应变分布规律。结果表明:管材焊缝区的减薄率仅为2.4%~5.5%,等效应变仅为0.05~0.10,变形程度相对母材区较小,主要发生几何位置移动。环向壁厚的最薄点位于以焊缝为中心的对称两侧士30°位置处。随着胀形区长度增大,管材破裂压力、减薄量、极限膨胀率均发生减小,胀形区轮廓逐渐偏离椭圆形,当长径比达到2.0时,已不再适合用椭圆函数描述。此外,胀形区长度增大过程中,管材从双拉向平面应变状态发生转变,在此基础上建立了焊管的成形极限图。     

多面壳体胀球时焊接接头变形的数值模拟和试验研究

用弹塑性有限元法模拟了多面壳体胀球时焊接头变形过程，并且云纹法和网络法对有限元结果进行了试验证。研究结果表明：胀形时内侧焊缝首先进入屈服，内侧应变大于外侧应变。板越厚，初始两面角越小，内侧焊趾应变越大，内外侧应变差越大。焊缝金属屈服强度低于母材，有利于缓和热影响区的变形，有利于棱角展平。     

铝合金马鞍形件充液成形工艺模拟分析

目的研究板材充液成形柔性制造高精度、高质量马鞍形件的工艺方法。方法利用有限元动力学显示分析方法,对充液拉深和液压胀形两种成形工艺方案进行分析,并对比分析减薄率和成形极限图判断工艺方案的合理性。结果针对铝合金马鞍形件,通过对比分析2种方案,充液拉深工艺中的最大减薄率达到14.3%,液压胀形最大减薄率为7.2%,位置均在型面补充件的顶部,2种方案的成形极限都在安全区域内,未见破裂现象。结论通过工艺模拟分析,得到对铝合金马鞍形件,采用一模两件液压拉深成形工艺较合理,成本较低,加工周期短,加工效率高,成形精度高。     

预拉深对气胀钛合金筒形件壁厚均匀性的影响

以钛合金筒形件为研究对象,针对传统气胀成形存在减薄率过大问题,开展了预拉深-气胀复合成形方法研究。采用数值模拟分析了传统气胀成形中筒底减薄率过大的原因,实验研究了不同加载路径对TA15筒形件减薄率的影响。结果表明:气胀成形的加载速度对减薄率有一定的影响,慢速气胀和快速气胀成形件最大减薄率分别为63.2%、54.2%,仅提高加载速度并不能满足壁厚均匀性要求;在有一定预拉深的情况下,通过热拉深-气胀复合成形,最大减薄率可减小到36.7%。热拉深-气胀复合成形工艺可有效改善成形件的壁厚分布均匀性.     

厚壁管低熔点塑性介质挤胀成形实验研究

采用低熔点塑性材料作为传力介质挤胀成形厚壁空心构件，研究了空心构件低熔点塑性介质挤胀成形机理和主要影响因素，分析了低熔点塑性介质挤胀管坯的成形过程和壁厚分布规律．研究结果表明：低熔点塑性介质挤胀成形时管坯和塑性介质两种材料同时发生塑性变形，管坯的变形流动是塑性介质的内压和冲头轴向挤压共同作用的结果；轴向压力和径向内压力的匹配关系是低熔点塑性介质挤胀成形工艺的关键；管坯胀形区的壁厚有较大的减薄，但与自然胀形相比壁厚减薄的程度较小。     

椭球壳体无模液压成形实验探索

对椭球壳体的整体无模胀形成形工艺进行了实验研究。实验壳体采用单曲率椭球内接多面壳体。对实验壳体的尺寸变化、变形过程中的表面应变分布、变形前后的壁厚变化规律进行了测试分析,探讨了壳体的趋球变形过程,壳体的长短轴变化趋势及塑性变形规律。实验证明,在封闭椭球壳体内塑性趋球规律仍然起作用,椭球无模液压整体成形工艺值得进一步探讨研究。     

薄壁罐气压胀形参数优化研究

为提高金属薄壁罐气压胀形的成形质量,减少壁厚减薄严重及皱折破裂等成形缺陷,采用数值模拟的方法,分析了摩擦因数、模具圆角半径、坯料厚度、胀形压力对壁厚减薄率、最大应力值、轴向收缩的影响规律,试验验证与数值模拟结果吻合。研究结果对工艺优化和过程控制具有实用意义。     

弯头推制中金属流动规律的研究

在用机械力将坯料金属管推挤成弯头时，通过研究刻划在坯料表面上正方形网格的变化，可以发现金属管变形时的流动规律，并定量地显示金属坯料沿径向和沿轴向的应变，据此又找到了计算各处壁厚数值的公式，从而可以判断各处壁厚减薄量是否超限。所发现的金属流动规律是：弯头内侧金属向两侧流动，外侧金属不流动，但有部分金属重新分布；弯头外侧壁厚与坯料原料相同，从外侧向内侧壁厚逐渐减薄，内侧壁厚减薄量最大。壁厚分布规律与弯头的实际应用要求一致，因而应当推广推制弯头。     

瓜瓣式多面壳体胀形成球变形规律研究EI

本文通过实验研究了瓜瓣式多面壳体液压胀形成球过程中壳体的变形规律。结果表明该种多面壳体的成球过程是其棱边非平角焊接接头平角化的过程。     

Numerical and experimental applications of the least-squares method to determine mode-II stress intensity factors for double fillet welded lap joints

Due to its simplicity, the least-squares method provides an efficient means to evaluate the stress intensity factors (SIFs) of cracks in complicated structures. This paper demonstrates numerical and experimental applications of the least-squares method to study mode-II SIFs of double fillet welded lap joints. In the numerical application, double fillet welded lap joints with different geometric parameters, including overlap length, weld leg size, plate thickness and plate length, were systematically analysed by the finite-element method combined with the least-squares method. The computed SIF results were then employed to develop the general formulae of the shearing fracture mode (mode-II) stress intensity factors. To validate the numerical results, three double fillet welded lap joint specimens were tested by a non-contact optical experiment using a common digital camera and a proposed image processing scheme. The measured crack shearing displacements near the crack tip were substituted into the least-squares procedure to obtain the SIFs of the specimens. The numerical and experimental results were in good agreement with the existing numerical results for double fillet welded lap joints provided in the handbook (Murakami, 1987). The non-contact optical experiment makes the field measurement of SIFs possible, which is very useful for fracture analysis or fatigue evaluation of structures like steel bridges, naval structures and offshore structures.     

复杂截面冷弯成形圆角减薄率工艺优化研究

目的 针对复杂截面车门中导轨冷弯成形过程复杂、道次繁多、Z字筋圆角减薄率过大等问题,基于车门中导轨冷弯成形工艺,优化Z字筋圆角冷弯成形工艺和减薄率。方法 利用COPRA FEA有限元仿真软件对车门中导轨成形过程进行分析,研究轧辊圆角半径、成形速度、成形策略等对圆角减薄率的影响,结合有限元分析手段不断优化工艺参数来实现中导轨Z字筋圆角精确成形,最终提出最优工艺方案并进行实验验证。结果 对于大圆角成形工艺,圆角处弯曲中性层完全位于料厚范围内,在料厚方向上既有压应力又有拉应力,壁厚减薄量较小;对于小圆角成形工艺,圆角处中性层偏出内弧面,在料厚方向上均受拉应力,壁厚只存在减薄的趋势。实验结果表明,Z字筋圆角厚度由1.33 mm变成1.46 mm,减薄率由原来的26.1%降低至18.89%。仿真结果表明,Z字筋圆角厚度由1.29 mm变成1.52 mm,减薄率由原来的28.3%降低至15.6%。对比仿真结果与实验结果可知,仿真分析最大误差为4.1%,仿真结果具有一定的可靠性。结论 最优工艺路线如下:采用大圆角、慢速成形,成形策略为中前期大圆角成形+后期小圆角成形,成形圆角半径分别为4.5、3.5、2.8、1 mm,弯折角度分别为45°、65°、78°、90°,该方案可以有效解决圆角减薄率过大的成形缺陷。     

Distribution of Residual Stresses in a Layer Containing a Welded Cylindrical Disk

By the method of conventional plastic strains, we study the distribution of residual stresses in a plane layer containing a welded cylindrical disk. For plastic strains symmetric about the median surface of the layer, we perform the numerical analysis of the distribution of residual stresses. It is shown that the radial stresses on the surfaces of the welded joint decrease and the hoop stresses increase as the radius of the disk increases.     

A study of fatigue crack growth from artificial corrosion pits at welded joints under complex stress fields

The paper studies the effects of artificial corrosion pits and complex stress fields on the fatigue crack growth of full penetration load‐carrying fillet cruciform welded joints with 45° inclined angle. Parameters of fatigue crack growth rate of welded joints are obtained from S‐N curves under different levels of corrosion. A numerical method is used to simulate fatigue crack growth using different mixed mode fatigue crack growth criteria. Using polynomial regression, the crack shape correction factor of welded joints is fitted as a function of crack depth ratios. Because the maximum circumferential stress criterion is simple and easy to use in practice, fatigue crack growth rate is modified using this criterion. The relationship of effective stress intensity factor, crack growth angle and crack depth is studied under different corrosion levels. The simulated crack growth path obtained from the numerical method is compared with the actual crack growth path observed by fatigue tests. The results show that fatigue cracks do not initiate at the edge or bottom of pits but at the weld toes where the maximum stress occurs. The artificial corrosion pits have little effect on the effective stress intensity factor ranges and crack growth angle. The fatigue crack growth rates of welded joints with pits 1 and 2 are 1.15 times and 1.40 times larger than that of the welded joint with no pit, respectively. The simulated crack growth path agrees well with the actual one. The fatigue life prediction accuracy using the modified formulation is improved by about 18%. The crack shape correction factor obtained using the maximum circumferential stress criterion is recommended being used to calculate fatigue life.     

钢制轮辋滚压成形数值模拟与实验研究

目的 解决合金钢制轮辋滚压成形精度低和圆角减薄难以控制等问题。方法 通过Solidworks建立钢制轮辋三维模型,并对轮辋滚压模型参数进行优化设计,确定材料应力–应变、接触边界条件,且根据节点线速度相等原理计算钢制轮辋滚压成形时间步长。运用有限元软件Simufact Forming分析不同工艺参数对成形厚度的影响,在此基础上,优化滚压成形工艺参数组合,并分析各道次滚压轮辋应力和应变的仿真结果,引入质点追踪技术,分析应力在每个增量步内的变化规律。结果 对比分析仿真与实验测试数据,发现仿真厚度与实际厚度基本吻合,验证了滚压工艺仿真的正确性。结论 增大摩擦因数有利于工件成形,但当摩擦因数增大到0.3后,对成形壁厚影响不明显。随着进给速度的增大,测点厚度增加,此时利于成形,但进给速度过大,侧向力变大,易造成工件偏移。降低转速有利于控制轮辋减薄。在成形过程中,一滚凹槽先产生较大应力,且应变较大;二滚预成形轮缘,该处应力和应变均较大,且最大等效应力出现在轮缘部位;三滚轮辋精确成形,应力分布更加均匀,圆角变形相对较小,轮辋圆角减薄率明显提升。     

6061铝合金飞机溢油口拉深成形研究

目的 掌握深腔薄壁溢油口拉深成形工艺,解决拉深成形过程中起皱和破裂问题,研究各参数对拉深成形的影响规律,最终成形出合格产品。方法 以6061铝合金飞机溢油口为主要研究对象,采用Dynaform有限元数值模拟软件建立有限元模型,分析成对拉深成形对材料流动的影响并与单一拉深成形进行对比,通过改变毛坯外形尺寸、凹凸模间隙和压边力等参数进行拉深成形模拟试验研究,最终通过拉深成形试验验证成形方法及各参数设置的合理性。结果 成对拉深成形能限制单一拉深成形圆弧开口位置材料收缩,改善开口处起皱和变形缺料的现象。随着凹凸模间隙的增大,最大减薄率逐渐降低而后升高,最佳成形凹凸模间隙为1.05t;随着压边力的增大,最大减薄率逐渐升高,最大增厚率逐渐降低,最佳成形压边力为50 kN;凹模圆角半径小于7 mm 时,板料最大减薄率逐渐减小,半径为4 mm时,最大减薄率下降最快,半径在7~8 mm范围内,板料最大减薄率趋于平稳,最佳成形凹模圆角半径为7 mm。结论 模拟得到了毛坯外形尺寸、凹凸模间隙和压边力等参数对拉深成形的影响规律,最终制造出了满足设计要求的产品,验证了各参数设置的合理性。     

大型弯头无模整体液压胀形新工艺的实验研究

提出了一种旨在用于大型管路系统的无模整体液压胀形制造弯头新工艺，成功地获得了一个厚度3．0mm，口径531．0mm，弯曲半径1310．0mm 的45．0°弯头实验件，其材料为Q235A该弯头初始结构为截面为正六边形的焊接扇形环壳结构，成形压力约为2．5MPa，实验表明，无模整体液压胀形法制造大型弯头造价低廉，简单可行。     

Analysis of non-loading carrying fillet welds joint using SGBEM

Fatigue failure is probably the most common type of failure in welded construction. It is usually initiates at a stress concentration area within the structure. The fatigue behavior of non-load carrying cruciform fillet welded joint has been studied extensively using boundary element method. The symmetric boundary element method for multiple cracks problem is derived using Betti's reciprocal theorem in auxiliary fictitious state. High order element is proposed to solve the double integrals. The analysis demonstrates that symmetrical Galerkin boundary element method (SGBEM) can be used effectively for analyzing non-load carrying fillet welded cruciform joints containing any number of surface and embedded cracks. The stress intensity factor and the magnification factors M _k are analyzed. General formulation for this kind of fatigue life estimation is derived for engineering design purpose. The fatigue life estimate results are consistent with the code of practice and those of other researchers. This can provide a good method for engineering design under fatigue loading conditions.