基于热加工图6082铝合金锻造工艺优化及强化机制研究

利用Gleeble-3500热模拟试验机对6082铝合金进行高温压缩试验,研究了在变形温度为300～500℃和应变速率为0.01～10.00 s~(-1)条件下6082铝合金的热变形流变行为。采用Zener-Hollomon参数法构建6082铝合金高温塑性变形的本构关系,验证试验的相关系数和平均相对误差分别为0.992%和3.100%。基于DMM(dynamic materials model)模型构建了不同应变量下6082铝合金的热加工图,合金的安全加工区域主要位于400～500℃, 0.025～1.000 s~(-1),并通过高温塑性变形行为的研究结果,优化了6082铝合金的等温锻造工艺,锻造工艺为:锻造温度450℃,真应变0.4(工程应变33%),应变速率0.200 s~(-1)。通过金象显微镜(OM)、拉伸试验和透射电镜(TEM)分析了该合金变形后的微观组织性能变化及强化机制。研究结果表明:6082铝合金的软化机制主要为动态回复,且固溶时效后析出相的形核及长大与基体中位错密度紧密相关。     

6082铝合金扭转冷作硬化的实验研究

以船用铝合金6082原材料为研究对象,探讨扭转冷作硬化对其拉伸力学性能的影响。通过扭转冷作硬化这一冷加工方法,对试样预加了6种不同角度的扭转塑性变形,并进一步对强化后试件的拉伸力学性能进行了测试,得到了不同扭转硬化角度下其拉伸性能的变化趋势和强化规律。     

Mn-Si-Cr系Q&P钢的准静态、动态力学行为对比

利用万能试验机和分离式霍普金森压杆装置(SHPB)对Mn-Si-Cr系Q&P钢分别进行了准静态和动态压缩试验。在应变速率为0.001、0.01、0.1 s-1和900、1 500、2 200、3 000 s-1情况下分别得到了准静态和动态压缩真应力-真应变曲线,并利用扫描电子显微镜进行压缩后的显微组织和断口分析,利用X射线衍射仪(XRD)对压缩变形试样进行物相分析。结果表明,准静态和动态压缩变形条件下,试验钢的真应力-真应变曲线均可大致分为弹性变形和塑性变形2个阶段,且没有明显的屈服平台。准静态压缩条件下应变速率强化效果不明显但应变强化效应较显著。动态压缩条件下应变强化效应不明显,但展现出一定的应变速率强化效应。准静态变形后,试样中心区域板条组织倾向沿近水平方向(垂直于压缩方向)定向排布。动态变形后,约有1/3试样发生了断裂,未发生断裂的试样中心出现45°方向剪切带,其附近板条组织发生了“屈曲”。准静态变形后残余奥氏体含量下降明显,而动态压缩试样中,残余奥氏体含量只有略微下降,且块状M/A岛内部出现扭曲变形与开裂,这可能是导致部分试样断裂的诱因。动态压缩破坏试样断口整体呈现45°剪切断裂,一端发生微孔聚集性断裂,另外一端发生剪切断裂。     

Mn-Si-Cr系Q&P钢的准静态、动态力学行为对比

利用万能试验机和分离式霍普金森压杆装置(SHPB)对Mn-Si-Cr系Q&P钢分别进行了准静态和动态压缩试验。在应变速率为0.001、0.01、0.1 s-1和900、1 500、2 200、3 000 s-1情况下分别得到了准静态和动态压缩真应力-真应变曲线,并利用扫描电子显微镜进行压缩后的显微组织和断口分析,利用X射线衍射仪(XRD)对压缩变形试样进行物相分析。结果表明,准静态和动态压缩变形条件下,试验钢的真应力-真应变曲线均可大致分为弹性变形和塑性变形2个阶段,且没有明显的屈服平台。准静态压缩条件下应变速率强化效果不明显但应变强化效应较显著。动态压缩条件下应变强化效应不明显,但展现出一定的应变速率强化效应。准静态变形后,试样中心区域板条组织倾向沿近水平方向(垂直于压缩方向)定向排布。动态变形后,约有1/3试样发生了断裂,未发生断裂的试样中心出现45°方向剪切带,其附近板条组织发生了“屈曲”。准静态变形后残余奥氏体含量下降明显,而动态压缩试样中,残余奥氏体含量只有略微下降,且块状M/A岛内部出现扭曲变形与开裂,这可能是导致部分试样断裂的诱因。动态压缩破坏试样断口整体呈现45°剪切断裂,一端发生微孔聚集性断裂,另外一端发生剪切断裂。     

时效热处理对6082-T6铝合金型材力学性能的影响

试验研究了淬火后停放时间及时效工艺对6082-T6铝合金型材力学性能的影响,结果表明,在综合考虑工业化实际生产条件下建议采用26h~30h的淬火后停放时间;6082-T6铝合金型材无淬火停放时最佳时效工艺为175℃×4h。     

7B52铝合金动态力学性能及断裂行为研究

通过对7B52铝合金进行动态压缩实验和准静态拉伸试验,结合微观组织的OM、SEM和TEM分析,研究了应变速率和取向对7B52铝合金准静态和动态力学性能及断裂行为的影响。结果表明:随着应变速率的升高,7B52铝合金流变应力呈现出先升高后降低的趋势;同一应变速率下,轧向(L向)强度均大于横向(T向)。7B52铝合金准静态加载时为穿晶韧性断裂机制。动态加载时,7B52铝合金内形成了绝热剪切带,剪切带内发生了以晶粒转动为机制的动态再结晶,断裂机制为沿晶脆性断裂。     

基于Hyperworks摩托车轮毂90度动态冲击仿真与测试对标的研究与应用

当前在摩托车轮毂行业,动态冲击仿真多用静态线性方法分析,边界条件与实际试验差别比较大,本文以铝合金材料非线性理论作为依据~([1]),结合动态有限元仿真技术,使用Radioss对某款铝合金轮毂进行动态冲击分析,并通过试验验证了该方法的有效性,该仿真方法的成功探索,有效地提高了仿真结果的准确性,为摩托车轮毂动态冲击试验提供了一种先进的求解方法。     

高应变率下纯钛动态压缩力学性能各向异性

利用Instron电子拉伸机和分离式霍普金生（SHPB）压杠实验装置,研究了准静态和动态压缩条件下织构多晶纯钛板TA2的力学性能,对织构多晶纯钛板法向ND、轧向RD、横向TD等三个方向进行了压缩实验,得到了不同应变率下的应力-应变曲线。结果表明对于轧制和退火纯钛板,准静态和动态压缩力学性能均表现出明显的各向异性,且规律一致：均为ND方向屈服强度最大,TD次之,RD方向最小。     

冲击载荷下低屈服比高强钢板的拉伸性能

通过室温下的仪器化冲击试验和静态拉伸试验,研究一种低屈服比高强度钢板在冲击载荷下的力学性能和断裂机理.结果表明:试验钢的组织由细小岛状马氏体与针状铁素体为主构成,马氏体体积分数为27.6%.与静态拉伸性能相比,在名义应变速率为100 s-1的冲击载荷作用下,试验用钢屈服强度提高31.6%,延伸率不降低.在静态和动态载荷下,该钢均以显微空洞长大聚集的方式发生韧性断裂,但显微空洞的形核和长大方式不同.在静态载荷下,显微空洞形核于颈缩区的铁素体晶粒内部或铁素体-马氏体两相界面处,空洞主要通过两相界面的脱开而形成长大;在动态载荷下,显微空洞主要形核于颈缩区的两相界面处,空洞主要通过马氏体粒子的开裂而形成长大.     

固溶处理对6082铝合金挤压棒材组织与性能的影响

对6082挤压棒材进行不同制度(单级、双级、三级)的固溶处理,通过力学性能测试,并结合高倍晶粒度测试和金相组织分析,研究了固溶处理对6082铝合金挤压棒材组织和力学性能的影响。结果表明:与单级和双级固溶制度相比,6082铝合金挤压棒材采用逐步升温的三级固溶,可以使粗大第二相得到充分溶解,获得较高程度的过饱和固溶体,棒材边缘无明显晶粒长大。时效后的抗拉强度和屈服强度均得到明显提高,其中最佳三级固溶工艺为515℃×45 min+550℃×35min+560℃×10 min。采用该固溶制度时,棒材截面晶粒细小均匀,时效后的硬度为123 HBW,抗拉强度和屈服强度提升到了414 MPa和392 MPa,断后延伸率为11.5%。     

Interlaminar Fracture of Composites under Tension and Compression

Interlaminar fracture of AS4∕3502 graphite∕epoxy material system is investigated using a double cracked‐lap‐shear (DCLS) specimen and a single cracked‐lap‐shear (SCLS) specimen. A fundamental feature of the designed specimens is their ability to be tested under net tensile and compressive loadings. The specimens exhibit mixed‐mode or mode II behavior depending on the loading direction. The specimens are designed to precipitate crack growth at a designed‐in site in a gage section. In the specimen design process, overall dimensions of the specimens are selected so that local disturbances in the stress field will not interact, there is adequate length to permit crack growth, and overall buckling will not occur under compressive loading. The experimental results confirm that the specimens and tests perform as designed, It is observed that: (1) There is an increasing resistance to crack growth under tensile loading; (2) interlaminar fracture under compression is a totally unstable process; and (3) tension and compression behaviors are considerably different. Fracture surfaces in the unstable regions from short beam shear and DCLS specimen tests exhibit similar characteristics.     

Effects of Shot Peening on Fatigue Properties of Zr-based Amorphous Alloys Containing Ductile Crystalline Particles

In this study, the fatigue properties of a shot-peened Zr-based amorphous alloy containing ductile crystalline particles were investigated, and fatigue processes were analyzed and compared with those of a non–shot-peened (as-cast) alloy. The microstructural analysis results of the shot-peened alloy surface indicated that the flexion and microstructural deformation were observed as the hot-peening time or pressure increased. However, the compressive residual stress formed on the shot-peened surface was approximately half of the ultimate tensile strength and was not varied much with shot-peening time or pressure. The fatigue limit and fatigue ratio of the shot-peened alloy were 368 MPa and 0.24, respectively, which were considerably higher than those of the as-cast alloy. This was because the compressive residual stress formed by the shot peening induced the initiation of fatigue cracks at the specimen interior instead of the specimen surface and, thus, enhanced the overall fatigue limit and fatigue life. These findings suggested that the shot peening was useful for improving fatigue properties in amorphous alloys.     

Yield behavior of a mild steel after prestraining and aging under reversed stress

Tubular specimens of mild steel are subjected to tensile prestraining and then aged under compressive stresses along the Bauschinger curve, at various temperatures below 175 °C. The compressive (reversed) stress imposed on the specimen during aging, called here the aging stress, is employed up to a maximum level of 90 pct of the prestress. Reloading tests in tension and in compression are carried out at room temperature, and the critical aging stress at which the yield stresses in the two reloading directions become equal is determined as a function of aging temperature. The critical aging stress decreases with increasing aging temperature and becomes constant at aging temperatures above 100 °C. Under such critical aging conditions, the aging index, i.e., the ratio of yield stress to prestress, rises with increasing aging temperature and approaches a saturation value of 0.86 at 150 °C. It is shown that stress aging is an effective means of reducing the Bauschinger effect while preserving the work hardening induced by the prestrain.     

Fabrication of lotus-type porous carbon steel by the continuous zone melting method and its mechanical properties

A lotus-type porous carbon steel with cylindrical pores was fabricated by the continuous zone melting method in a pressurized mixture of hydrogen and helium gases. The porosity increases with increasing partial pressure of the hydrogen gas, while the pore diameter remains almost constant, independent of the pressure. The ultimate tensile strength of the specimen with cylindrical pores parallel to the tensile direction is lower than the estimated value, assuming that the strength is decreased in proportion to the decrease of the cross-sectional area of the specimen, while the yield strength is higher than the estimated value. The compressive yield strength is also higher than the estimated value. The increase in yield strength is considered to be due to precipitation strengthening. The tensile strength is increased by quenching and tempering, while the elongation decreases. Such mechanical properties are discussed in terms of the microstructural analysis.     

不同应力条件下硬岩强度与破裂特性试验研究

深部工程围岩内的岩石可能处于一维、二维和三维应力状态下,分别对应室内单轴压缩、双轴压缩和真三轴压缩试验中岩样的应力状态。通过开展单轴、双轴和真三轴压缩试验,系统研究了不同应力状态和水平下岩石非常规破坏的发生机制。不同高宽比和宽厚比岩样的单轴压缩试验结果表明：随着岩样厚度的增加,单轴抗压强度单调增加;随着岩样高度的增加,单轴抗压强度往往先增加后减小,且矮薄岩样更容易发生岩爆和板裂等非常规破坏。双轴或真三轴压缩试验中岩样的抗压强度均表现出明显的中间主应力效应。在相同最小主应力下,随着中间主应力的增加,岩样的双轴抗压强度和真三轴抗压强度均呈先增加后减小的变化趋势,双轴抗压强度增长率则呈先减小而后小幅增大的趋势。通过定义强度增量参数ν和中间主应力位置参数λ构建了指数岩石真三轴强度准则。低围压限制、非对称围压限制和短裂纹扩展路径是引起岩石非常规破坏的主要条件。     

Stress corrosion cracking of an aluminum alloy under compressive stress

Stress corrosion cracking (SCC) of 7075 aluminum alloy in a 3.5 pet NaCl aqueous solution under compressive stress was investigated using modified WOL notched specimen. The result showed that SCC could occur if an applied compressive displacement was larger than a critical value. Finiteelement analysis indicated that there was a stress concentration and the stress components were negative at the notch tip under the compressive displacement. Since the unloaded displacements were equal but opposite to the loaded ones, no stress relaxation occurred throughout SCC. Thus, the SCC was induced by compressive stress. The threshold stress intensity nucleating SCC from the notch under the compressive applied stress was 27.6 MPa m^1/2, but the corresponding value under tensile stress was 8.3 MPa m^1/2. Besides, the incubation period for SCC under compressive stress was one order of magnitude longer than that under tensile stress in the sameK ₁ The fracture surfaces of SCC under compressive stress were quite different from those under tensile stress. The latter was composed of intergranular but the former was quasi-cleavage characterized by parallel striation pattern. Formerly Student at Beijing University of Iron and Steel Technology     

Q345钢连铸坯压缩状态下的高温力学性能

Q345钢应用广泛,其在拉伸状态下的高温力学性能已有部分研究,但高温压缩力学性能数据匮乏。利用Gleeble-3500热模拟机对Q345钢连铸坯试样进行了热压缩试验,研究了应变速率为0.01 s-1时试样在压缩状态下的屈服强度、抗压强度和弹性模量等随温度(973~1 673 K)的变化规律,同时探讨了试样在1 473 K时不同应变速率(0.001、0.01和0.05 s-1)下的高温力学性能。结果表明,在973~1 373 K温度内,屈服强度和抗压强度都表现出对温度的敏感性。屈服强度由90降到24 MPa,抗压强度由202降到40 MPa。在1 373~1 673 K温度内,屈服强度和抗压强度降幅都很小。弹性模量随温度的升高而减小,其值在1 473和1 573 K温度下相差最大,达1 712 MPa。屈服强度对应变速率的变化并不敏感,均在20 MPa左右,而极限抗压强度由28增加到45 MPa。最后根据试验数据绘制了Q345钢连铸坯在热压缩状态下的屈服强度等高温性能参数随温度变化的关系曲线,可为轻/重压下等技术提供参考数据。     

Numerical Simulation on Damage and Failure of Brittle Rocks under Different Confining Pressures

A numerical analysis has been conducted to evaluate the effect of confining pressure on the damage evolution and the fracture process of brittle rock materials by using the rock failure process analysis code (RFPA2D). A fractal dimension D associated with material damage and a damage variable ω are defined to describe the damage process of the specimen subjected to tensile or compressive load. We find that the spatial distribution of microfractures is fractal and has very good statistical self-similarity in the specimen under different confined conditions. The fractal dimension D increases progressively with loading. Meanwhile, the damage variable ω develops from 0 to 1, and the specimen failure is characterized by the critical damage variable ωc with 0.4 ? ωc ? 0.8. The initial damage is delayed by the confining pressure. The confining pressure plays an important role in the mode of rock failure in numerical simulations. The tensile microfractures dominate near the brittle splitting of the specimens under no and low confining pressure. Conversely, a few tensile microfractures appear in the ductile shear failures of the specimens under immediate or high confining pressures. The tensile microfractures run through all failure processes in the specimen under uniaxial tensile loading. The stress-strain curves are also obtained in numerical simulation. The results show that the specimen is strengthed by the confinement and fails according to Mohr-Coulomb failure criterion.     

单轴压缩试验中减弱端部效应新型方法研究

为了减弱端部效应对单轴抗压强度测量的影响,提出一种新型的单轴压缩试验方法。该方法采用与试件材质相同的岩石作为垫块进行单轴压缩试验,设置了（25+50+25）mm和（20+60+20）mm 2种试件高度组合进行试验,并与高度为50 mm、60 mm的单一试件的试验结果进行对比。结果表明：该新型试验方法可以降低单轴压缩试验中端部效应对测量岩石单轴抗压强度的影响,并得到更为均匀的径向应变;（25+50+25）mm和（20+60+20）mm组合试件相比高度为50 mm和60 mm的单一试件,单轴抗压强度分别降低了38.41%和39.69%,相比标准试件,单轴抗压强度也有所降低。数值模拟结果表明：无论有无端部摩擦,组合试件的单轴抗压强度均与理想状态下模拟所得的岩石试件的单轴抗压强度值接近;无端部摩擦时单个试件与组合试件具有均匀的径向应变;有端部摩擦时组合试件的径向应变较为均匀。数值模拟结果证明了该新型试验方法减弱了端部效应,但并未完全消除。     

转向节用贝氏体型非调质钢的高周疲劳性能

利用旋转弯曲疲劳试验方法对比研究了新开发的两种转向节用贝氏体型非调质钢的高周疲劳性能。结果表明,两种不同碳含量的贝氏体型非调质钢具有细小均匀的贝氏体铁素体+M-A岛组成的粒状贝氏体组织;两者具有相当的强度水平和疲劳性能,但其疲劳性能低于同等强度水平的调质钢。与锻态相比,正火处理后,试验料的抗拉强度和疲劳强度均有一定程度的降低,但屈强比和疲劳极限比明显提高。对疲劳断口的分析表明,试验料的疲劳裂纹均起源于表面基体,疲劳裂纹以准解理机制扩展。裂纹扩展速率试验表明,含碳量较低的试验料的疲劳裂纹扩展速率da/d N明显低于含碳量较高的试验料。