Strain distribution of strips with spherical inclusion during cold rolling

The deformation of 304 stainless steel strips with a spherical inclusion during cold rolling was simulated by 3D finite element method, and the strain distribution was calculated for a variety of the material attribution of inclusion (hard inclusions and soft inclusions) and the inclusion size (10, 20, 30, 40, and 50 μm). During rolling, the strain in front of inclusion is larger than that in rear of inclusion for both the hard and soft inclusions. For hard inclusions, the strain in front and rear of inclusions is larger than that of inclusions, and the maximum and minimum strains increase with the increase of inclusion diameter (from 10 μm to 50 μm). For soft inclusions, the strain in front and rear of inclusions is smaller than that of inclusions, and the maximum and minimum strains decrease with the increase of inclusion sizes when the inclusion diameter is larger than 20 μm but increase when the inclusion diameter is smaller than 20 μm. Finally, the relationship between the inclusion deformation and the crack generation was discussed.

EXPERIMENTAL INVESTIGATION ON CHANGE OF COLDWORKING RESIDUAL STRAIN OF HOLE IN ALUMINIUM ALLOY SHEET

An experimental study on degeneration of the coldworking residual strainduring different cyclic loadings is presented. The expenmental results obtained showthat the residual strain of squcezing dislributes under power series law ε= axb overthe horizontal line of the stress on both sides of the cenual hole. and that when the max-imum real stress at the hole is lower than the yield stress of the material. the degeneration of residual strain has a sudden change during cyclic loading, and the closer to thehole side, the more serious the degcneration.

Influence of stress path change on the resistance to plastic deformation of cold rolled sheets

Flat workpieces have been tested in order to investigate the influence of stress path change （loading mode） while keeping strain path unchanged. These investigations are pertinent to the testing of cold rolled strips and to subsequent forming. The workpieces which first compressed by plane strain compression in thickness direction were then tested in perpendicular direction in order to measure the influence of strain and stress path. The tension workpieces came from flat die compression test at different deformation histories. Two different materials were investigated： 18/8 Ti stainless steel and AW-1050 aluminium. The results show that the plastic flow by tension in lengthwise direction after pre-strain by compression in thickness direction will begin at an appreciably lower stress than that of the workpieces unloaded after pre-compression. Comparing with two materials, it can be seen that both 18/8 Ti stainless steel and AW-1050 aluminium behave similarly. The drop in yield stress is lower for AW-1050 aluminium than that for 18/8 Ti stainless steel. However, reloading in different directions than in the precious step results in significantly higher strain hardening.

Deformation and Densification Laws of Powder Cold Forging

The deformation and densification laws of preform upsetting and closed-die forging were researched based on experimental results of cold forging of deoxidized Fe powder sintering porous material under different initial conditions such as friction factor, ratio between height and diameter and relative density. The fracture limit criteria＂ for powder cold-forging upsetting and the limit strain curve were achieved. The effect of friction facto,, ratlt, between height and diameter and relative density on fracture strain limitation was emphatically analyzed. The limit process parameter curves for the deformation of upsetting were also confirmed. Laws of deformation, densification and density distribution for closed-die forging of powder perform during cold-forging were further analyzed and discussed with the help of experimental phase analysis. As a result, this experiment established theoretical foundations for the design of preform and die as well as optimization of technological process parameters.

Effect of strain rate on microstructure and mechanical properties of a Mg-9Li-2Zn alloy sheet

A two-phase Mg-9Li-2Zn alloy sheet is made by cold-rolling at room temperature, and the formability of it at room temperature is investigated in this study. Uniaxial tension tests are carried out for various strain rates between 0.5 mm/min and 250 mm/min, and the microstructural changes during the tests are observed. The sheet has high formability at comparatively low strain rates. Maximum elongation amounts to 40%. However, ductility decreases with the increase of strain rate. Even at room temperature, the stress is also sensitive to the strain rate. There are many large dimples at comparatively low strain rates, and small dimples occur at high strain rates, it shows fine sub-grains come into being.

Study on Modification of Polymer Properties by the Cold Drawing Process

Polymers have a wide diversity of applications, ranging from therapeutics delivery to tissue engineering. While advances in polymer chemistry have facilitated synthesis and development of new polymers, increasing efforts have also been directed to engineer properties of existing polymers. One of the common approaches to modify polymer properties is cold drawing, which can align polymer chains and orient the chains in a crystalline manner. Regarding the industrial significance of cold drawing in polymer engineering, this study used semi-crystalline high density polyethylene (HDPE) as a model to examine the effect of cold drawing on the anisotropic mechanical properties of polymers. During cold drawing, the yield strength of the polymer was shown to be in a positive relationship with the strain rate, and the hardness of the cold-drawn region was demonstrated to be significantly enhanced. Our results confirmed the feasibility of engineering the properties of polymers by applying tension for plastic deformation, and highlighted the importance of precise control of the strain rate in the treatment.

Influence of Degree of Cold-Drawing on the Mechanical Properties of Low Carbon Steel

Low carbon steel metal is used for the manufacture of nails. Steel wire with <0.3% C content is cold-drawn through a series of drawing dies to reduce the diameter of the wire to the required diameter of the nails. A 0.12%w C steel wire cold drawn progressively by 20%, 25%, 40% and 50% was investigated. The influence of the degree of cold drawing on the mechanical properties of the carbon steel material were studied using the tensile test, impact test and hardness test experiments in order to replicate the service condition of the nails. The tensile test was done on a Montanso? tensometer to investigate the yield strength and the tensile strength of the material as the degree of deformation increases. An Izod test was used to determine the impact toughness of the steel using the Hounsfield impact machine and the hardness numbers were obtained for the different degrees of drawn deformation of the steel on the Brinnel tester. The study used the stress-strain relationship of the tensile test experiment to study the effect of the degree of cold-drawing deformation on the yield strength and tensile strength properties of the low carbon steel. The yield strength of the material was observed to reduce with increasing degree of cold-drawing, an indication of reduction in the ductility and the tensile strength of the material reduced with increasing degree of cold-drawn deformation. The ability of the material to resist impact loads when nails are hammered reduced with increasing degree of drawn deformation as a result of strain hardening of the material after the drawing operation. However the resilience of the material to further cold drawn deformation increased with increasing degree of deformation as evident in the Brinnel hardness number which increases with the degree of drawing deformation. This is an indication of the material’s approach to brittleness as the degree of drawn deformation increases.

砂岩冻结/解冻过程蠕变特性研究

寒区岩体长期经受荷载与冻融的共同作用,若不考虑冻融过程对其长期力学行为的影响,将会给寒区工程建设和安全运营带来重大的安全隐患。为此,以寒区某边坡工程砂岩为研究对象,通过开展不同冻结温度下的冻结/解冻过程单轴分级加载蠕变试验,使岩石在同一应力状态下处于冻结和解冻过程,真实再现寒区工程岩体长期力学响应特征。以此研究冻结/解冻过程对岩体长期力学特性的影响,并对其蠕应变、稳态蠕变速率及长期强度等宏观力学指标进行量化分析。结果表明:(1)砂岩冻结过程先后经历冷缩阶段、冻胀阶段和稳态蠕变阶段,解冻过程只经历融缩阶段和稳态蠕变阶段;冷缩阶段和融缩阶段砂岩发生收缩变形,冻胀阶段则发生膨胀变形;(2)冻结/解冻温度为-5℃/25℃、-10℃/25℃、-15℃/25℃时,砂岩蠕应变较常温状态下蠕应变增幅范围分别为102%~193%、81%~126%、105%~194%,解冻后稳态蠕变速率较冻结前最大增长3.65倍、4.31倍、5.56倍,冻结/解冻过程蠕变砂岩的长期强度是常温状态下长期强度的96.33%、88.52%、75.44%;(3)应力对冷缩、冻胀变形的产生起抑制作用而对融缩变形的产生起促进作用;冻结温度越低,冻胀变形和解冻后融缩变形越明显。文章提出的将蠕变与冻融过程相结合的试验方法能较为真实地反映工程实际,该方法为寒区岩体工程长期稳定性评价提供新途径。

预应变对S30408不锈钢力学性能和马氏体相变的影响

为了探究不同预应变量下S30408不锈钢力学性能的变化规律,课题组在室温下对S30408不锈钢开展不同预应变量下的单轴拉伸试验,分析了预应变对其力学性能及马氏体相变的影响规律,在此基础上建立了考虑预应变影响的修正Ludwigson模型,并结合基于Johnson-Cook的脆化模型合理预测预应变后材料力学性能。结果表明:随着预应变量的增加,S30408不锈钢的屈服强度明显增加,抗拉强度缓慢增加,断后延伸率降低;利用金相和X射线衍射试验获取不同预应变量下微观组织和析出相成分,发现在预应变量大于9%后,S30408不锈钢开始逐渐出现形变诱导的马氏体相变。课题组的研究实现了不同预应变量下的S30408不锈钢应力-应变关系的合理评价。

大青叶砧木对钟花樱品系樱花花期及抗寒性的影响

[目的]研究大青叶砧木对于钟花樱(Cerasus campanulata)品系樱花花期及抗寒性的影响。[方法]2019—2021年以红粉佳人(Cerasus campanulata‘Hongfenjiaren’)、中国红(Cerasus campanulata‘Zhongguohong’)、河津樱(Cerasus campanulata‘Kawazu-zakura’)、台湾牡丹樱(Cerasus campanulata‘Double-flowered’)4个钟花樱品系的钟花樱砧木嫁接苗为对照,对上述品种的大青叶砧木嫁接苗进行观测,比较花期差异及1年生枝条抽条情况。分别在0、-5、-10、-15、-20℃低温胁迫下,测定1年生枝条丙二醛(MDA)含量、可溶性蛋白含量、脯氨酸含量、超氧化物歧化酶(SOD)活性等生理指标,并利用隶属函数法进行综合评价。[结果]上述4个品种的大青叶砧木嫁接苗初花期比钟花樱砧木嫁接苗初花期分别晚8.7、8.3、7.3、6.3 d。露地越冬条件下,除河津樱大青叶砧木嫁接苗发生轻微抽条现象外,其余苗木抽条现象较为严重。随着温度的降低,所有苗木的MDA含量、可溶性蛋白含量持续上升,脯氨酸含量及SOD活性呈先上升后下降趋势。隶属函数分析表明,4个品种大青叶砧木嫁接苗的抗寒能力排名靠前。[结论]相较于钟花樱砧木嫁接苗,大青叶砧木嫁接苗木花期较晚,抗寒能力较强,河津樱大青叶砧木嫁接苗可在北京地区小环境较好区域露地越冬。

针刺与火龙药灸治疗风寒阻络型腰肌劳损临床研究

目的 探究风寒阻络型腰肌劳损患者应用针刺及火龙药灸的效果。方法 选择2020年3月—2022年2月在江西中医药大学附属医院接受治疗的66例风寒阻络型腰肌劳损患者作为观察对象,采取随机数字表法将其分别纳入对照组(33例)及观察组(33例),对照组应用针刺联合艾条灸,观察组应用针刺联合火龙药灸。对比两组治疗总有效率、治疗前后腰痛症状量化积分。结果 观察组治疗总有效率为93.94%(31/33),高于对照组的75.76%(25/33)(P<0.05)。治疗14 d后,两组腰痛症状量化积分中压痛、腰部功能障碍等维度评分及总分均低于治疗前,观察组腰痛症状量化积分各维度评分及总分均低于对照组(P<0.05)。结论 对腰肌劳损风寒阻络型患者采取针刺联合火龙药灸,可改善其腰椎疼痛、功能障碍等症状,促进腰部恢复正常活动功能,减轻腰痛症状对其日常生活的影响。

冷轧加工率对5182-O铝合金汽车板性能和织构的影响

目的研究冷轧变形量对5182铝合金汽车板力学性能、塑性应变比、金相及织构的影响,系统解释5182铝合金汽车板的强化机理和成形性变化机理。方法采用X射线衍射仪、金相显微镜和万能拉伸试验机研究不同冷轧加工率下5182-O铝合金的力学性能和显微组织变化规律。结果50%和75%冷轧加工率的样品强度无明显差异,25%冷轧加工率的样品偏低约3 MPa。塑性应变比加权平均值rm随冷轧加工率的增大而减小,几乎呈线性关系,塑性应变比各向异性度Δr则先减小后增大,延伸率和应变硬化指数则无明显差异。当冷轧加工率从25%增至50%时,平均晶粒尺寸减小了约24%,当冷轧加工率从50%增至75%时,平均晶粒尺寸仅减小了1~2μm。不同冷轧加工率下的5182铝合金连退再结晶后均表现出较弱的织构强度,Cube织构未占主导地位,仍保留了较多的轧制织构。S、Copper和Brass织构的体积分数随冷轧加工率的增大而有所减小,Goss和Q织构的占比有所增大,Cube织构的占比则变化不大。结论冷轧加工率影响了5182-O铝合金汽车板连退后的晶粒尺寸,进而改变了强度。晶粒尺寸和屈服强度的关系符合经典Hall-Petch以及新Hall-Petch关系式。受不同再结晶形核机制竞争关系的影响,轧制织构随冷轧加工率的增大而稍有减少,导致45°方向的塑性应变比和rm逐渐减小,Δr则先减小后增大。

寒潮对钻孔体应变的影响特征与机制

中国是寒潮天气多发的国家,但寒潮对钻孔体应变观测的影响特征与机制如何,截至目前还鲜有针对性的典型个例研究。为此,本文以2022年11月27日—12月1日发生在江苏省的寒潮事件为例,并采用数字信号处理和理论气压负荷计算等方法,率先对江苏省内5个钻孔体应变台进行了系统分析。结果表明:①在较大范围内,寒潮可以导致气温和气压出现群体性突变,其中,前者的骤降幅度可达17.51℃、后者的涌升幅度高达29.23hPa。②寒潮天气中的气压涌升是导致钻孔体应变出现大幅压性变化的主因,其变形的持时在2612~3454min之间,最大变幅可达174.57nstrain,形态则与气压变化高度相似。③徐州台、连云港台、南通台和溧阳台对非周期气压的响应存在滞后效应,滞后时长介于52~306min范围内;新沂台则能超前响应气压,超前量为92min。以上认识将有助于寒潮干扰的客观识别。

冷喷涂颗粒临界速度预测的数值模拟

采用ABAQUS有限元软件建立了冷喷涂单颗粒撞击基体的耦合欧拉-拉格朗日四分之一模型,基于颗粒和基体形状变化以及等效塑性应变分布模型结果预测粒径25μm钛颗粒和30μm铝颗粒撞击7B04铝合金基体形成机械咬合与冶金结合的颗粒临界速度,并进行了数据有效性验证,研究了颗粒粒径、颗粒和基体初始温度对临界速度的影响。结果表明:根据模拟得到的颗粒/基体形状变化和等效塑性应变分布,预测得到粒径25μm钛颗粒、30μm铝颗粒的临界速度分别为680,700m·s^(-1),预测值与经验关系式估算值相对误差均小于11%,说明该方法准确;随着颗粒粒径增加、颗粒初始温度降低、基体初始温度降低,临界速度增大,其中颗粒初始温度对临界速度的影响较小,颗粒粒径和基体初始温度的影响显著。

松嫩平原几个柳树杂交品系抗寒性试验

为探讨几个柳树杂交品系的抗寒性,对近年在试验林内生长性状表现较好的6个灌木柳新品系(4#、8#、15#、16#、18#、25#)进行低温冷冻和冻后生长恢复试验,检验杂交品种的抗寒性。以不同时间为主处理,以5 d为时间间隔,设置4个时间梯度,以不同品系(品种)为副处理,以杞柳为对照开展柳树杂交品系抗寒性试验。结果表明:抗寒能力依次为18#>4#>杞柳>16#>25#>8#>15#,18#表现突出,抗寒性较强。当受到长时间低温影响时,25#、8#和15#电解质渗出率高于50%,出现了不同程度的冻害,当冷冻时间15~20 d时,试验中所有参试品系(品种)的电解质渗透率都在50%以上,会影响柳树生长发育,但还未达到死亡时间。

全铝制低温水箱冷热冲击耐久性优化设计

为解决冷热冲击试验中全铝制低温水箱扁管泄漏的问题,分别提出了扁管加宽、改O型集流管和增加隔板3种设计调整方案,并使用有限元分析软件Abaqus对原设计方案以及3种调整方案下的全铝制低温水箱进行有限元分析(FEA),得到泄漏区域内扁管的最大局部应力和最大塑性应变及其分布情况,以冷热冲击寿命和扁管泄漏的数量和位置为考查指标进行冷热冲击台架试验,结果表明,冷热冲击寿命与最大局部应力和塑性应变成反比,试验件泄漏扁管位置与局部应力及塑性应变分布规律一致,FEA结果与试验验证结果一致性较好。因此,为延长全铝制低温水箱冷热冲击寿命,方案顺序优化为使用O型集流管、使用窄扁管、使用双隔板。

草菇耐低温菌株的诱变选育与鉴定

在草菇V23原生质体形成和再生的最佳条件下制备原生质体。分别用紫外线(UV),60Co-γ射线,硫酸二乙酯(DES)对原生质体进行复合诱变。初筛、复筛获得耐常规低温(4℃)10d的菌株VH。栽培实验证明:VH在26℃下的生物学效率明显优于V23(CK),且差异极显著。同工酶分析表明:VH过氧化物同工酶,酯酶同工酶谱带数量及酶活性均发生变化;RAPD实验显示:VH相对于V23的变异系数为0.213。VH菇体正常,味道鲜美,食用后无毒副作用。氨基酸组成分析表明:除总氨基酸和谷氨酸含量VH高于V23外,其它氨基酸差异不明显。VH遗传性状稳定,是具有潜在应用价值的优良菌株。

连续定向凝固铜棒及其冷加工后的组织和力学性能

研究了连续定向凝固铜棒及对其进行大变形量冷加工后的线材的微观组织和力学性能。凝固铜棒具有纵向连续柱状晶组织,塑性优异,伸长率达到50.5%。经过冷轧和冷拔,柱状晶组织细化为纤维晶组织,并产生显著的加工硬化。经过真应变为3.6的冷变形加工,其抗拉强度由未变形的140MPa提高到418MPa,伸长率则下降了近70%。断口形貌观察表明:凝固铜棒、轧制后的铜杆及拉拔后的铜线都是穿晶韧性断裂,其微观断口均呈山峰状,且峰顶依次逐渐尖锐。

寒区输油管道基于应变设计的极限状态研究

寒区输油管线沿线地质环境复杂,滑坡、冻胀、融沉等自然灾害会导致管道形成大差异变形量.而差异变形量所引起的应力应变行为直接影响管道的安全服役性能,严重时会使管道破坏失效.基于寒区输油管道在实际服役工况下的受力变形条件,充分考虑冻胀效应、油压效应和热应力效应对输油管道的影响,分析了不同长度、壁厚、油压条件下轴向拉伸应变的分布规律及其影响因素.基于轴向应变设计理论准则,建立了上述条件下输油管道的极限服役状态,得到了对应状态下输油管道的许应最大极限冻胀变形量.结果分析表明,采用基于应力的设计准则偏保守,采用基于轴向应变的设计准则能更多的利用管材的变形性能.可为管道的合理设计、安全评价、完整性管理提供一定的理论参考.

水稻冷抗的动态模型分析

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