柱状晶CuAlBe合金丝的性能

用热型连铸法制备具有柱状晶组织的CuAlBe合金丝,并比较其与单晶CuAlBe的性能。试验结果表明,柱状晶与单晶一样具有优良的超弹性及应变恢复率,其弯曲疲劳寿命介于单晶的抛光与未抛光状态之间。CuAlBe柱状晶合金加热到500℃时组织无变化,加热到700℃时析出α相,使焊接后的应变恢复率稍有下降。CuAlBe柱状晶合金可进行不小于30%的塑性变形。     

Cu-Al-Be超弹性合金的力学性能研究

用热型连铸法制取直径为1.2mm的Cu-Al-Be超弹性合金丝,通过弯曲疲劳试验和拉伸试验,得出了Cu-Al-Be超弹性合金丝的试验结果。该合金可恢复应变量大,其数值不低于20%,最大应变高达40%;铸态下弯曲疲劳试验结果达50283次,经热处理后,弯曲疲劳试验达168480次。这些结果表明,在工程实际中Cu-Al-Be合金极有可能成为被广泛应用的新型超弹性合金。     

热型连铸超弹性CuAlNi合金丝的拉伸疲劳性能

用热型连铸法以不同速度连铸了φ1.5的柱晶CuAlNi合金丝,研究其拉伸疲劳性能.结果显示：铸态下,连铸速度由240mm/min提高到360mm/min时合金丝由于晶粒细化提高了疲劳寿命;铸态下少量γ2对拉伸疲劳没有显著影响;疲劳拉伸中柱晶晶界开裂,阻隔了疲劳裂纹扩展,降低了疲劳裂纹对表面缺陷的敏感性,有利于提高疲劳寿命.     

热型连铸超弹性CuAlNi合金丝的拉伸疲劳性能

用热型连铸法以不同速度连铸了φ1．5的柱晶CuAlNi合金丝,研究其拉伸疲劳性能。结果显示:铸态下,连铸速度由240mm／min提高到360mm／min时合金丝由于晶粒细化提高了疲劳寿命;铸态下少量γ2对拉伸疲劳没有显著影响;疲劳拉伸中柱晶晶界开裂,阻隔了疲劳裂纹扩展,降低了疲劳裂纹对表面缺陷的敏感性,有利于提高疲劳寿命。     

热型连铸CuAlBe柱状晶的各向异性

热型连铸CuAlBe形状记忆合金管接头具有柱状晶组织。为了研究管接头扩径时垂直于柱状晶生长方向的力学性能与组织的各向异性,用热型连铸板状试样模拟了管接头,原位观察和测量了板状试样横向拉伸时10个晶粒的变形。发现各个晶粒的拉伸卸载曲线可分为形状记忆型和超弹性型。不同形状记忆型曲线表明,应力诱发β'和γ'相变。拉伸曲线的多样性表明,柱状晶组织横向拉伸时为马氏体形成和稳定化各向异性、弹性各向异性以及相变滞后各向异性。这些各向异性强烈影响管接头的扩径率及相变滞后。     

柱状晶CuAlBe超弹性合金丝的等温变形

对热型连铸制备的柱状晶CuAlBe超弹性合金丝做等温变形试验,研究柱状晶在变形过程中组织和性能的变化.等温温度从400℃到600℃,变形量从25％到62.5％.结果表明,变形温度为450～550℃,在所研究的变形量内都能得到以β相为主及少量α相的柱状晶组织,力学性能与变形前大致相同,但残余变形大大增加.低于450℃变形产生马氏体,变形量增大时还导致晶界裂纹.高于550℃变形则产生十字星形γ2.后两者都使力学性能急剧下降.     

热型连铸CuAlMn合金丝的冷加工性能

用热型连铸法制备了柱状晶CuAIMn合金丝，经800℃固溶处理，不同温度退火后做冷轧试验，研究其在单一β相下的冷加工性能。冷轧结果表明，250℃退火的冷加工性能最优，而400℃退火由于发生贝氏体转变，冷加工性能急剧下降。细化晶粒可较大地提高冷加工性能。拉伸结果表明合金退火后有较好的超弹性，伸长率与冷加工性能的变化一致。     

柱状晶Cu-Al-Ni形状记忆合金的性能

用具有定向凝固特点的热型连铸工艺制备了Cu-Al-Ni形状记忆(SMA)合金丝.金相检验显示合金丝具有轴向排列的柱状晶组织.XRD分析表明,其基体β1相的生长方向为(100),分散度为10°～12°.合金丝经约20次的弯曲训练后形状恢复率非常稳定,最高可达100%;最大可恢复应变为10%,显示了优良的记忆功能.拉伸试验显示其抗拉强度最高达910 MPa,伸长率18.76%,与单晶组织相近而远优于多晶组织;拉伸断口出现缩颈,表明晶体发生了滑移.连铸工艺的稳定性对合金丝的力学性能有很大影响.     

热型连铸单晶铝的力学性能的研究

对直径为4 mm的热型连铸铝单晶线材的室温拉伸性能和循环弯曲性能进行了测试,并对其断口微观形貌进行了观察。结果表明:与多晶铝试样相比,热型连铸单晶铝屈服强度变化不大,抗拉强度降低了42.7%,伸长率和断面收缩率分别提高了111.5%和575%;弯曲疲劳寿命明显提高;单晶铝的断口呈扁尖状,断口附近滑移线相互平行且均匀分布,为典型的韧窝结构。     

连铸速度对CuAlNi记忆合金晶粒长大及弯曲疲劳的影响

以4种速度连铸了柱状晶组织的CuAlNi记忆合金丝并热处理，检验其晶粒长大及弯曲疲劳性能。连铸速度大于240mm／min，72相的析出被抑制；速度达480mm／min时由于凝固前沿液相受到激冷而形成等轴晶。360mm／min为柱状晶加热长大的临界连铸速度。超过此速度，加热时晶粒将急剧长大。临界连铸速度以下提高连铸速度可细化晶粒，经热处理消除内应力后，弯曲疲劳断裂次数可大幅提高。     

应变片位置的应变水平对旋转弯曲疲劳试验的影响

旋转弯曲疲劳试验是检测航空导管合格率的重要手段之一。在无扩口导管旋转弯曲疲劳试验中，通常将应变片粘贴在靠近导管承受最大应力处，但二者之间难以避免地存在误差，影响试验结果。针对此问题，基于应力-应变的理论分析，采用Abaqus软件对7种常见规格的TA18无扩口导管进行有限元仿真模拟，得到其应变片位置处的应变值及导管最大应变值，并进行试验验证。结果表明：导管实际产生的最大应变与应变片位置处所测得的应变值的相对误差在7%左右。参照航标，采用以应变片读数低于理论应变值5%的修正方法来进行试验，对确保试验结果的准确性具有一定的指导意义。     

汽车稳定杆用 55Cr3弹簧钢室温旋转弯曲疲劳性能

从汽车稳定杆用钢的实际应用需求出发,采用横向轴向应变控制方法,在应变循环比 R为－1,频率 83Hz和室温环境下,测试了 55Cr3弹簧钢旋转弯曲疲劳性能,得到了试样的 S-N曲线。并通过扫描电镜观察疲劳断口,研究了 55Cr3弹簧钢旋转弯曲疲劳特性。结果显示：生产的汽车稳定杆用 55Cr3弹簧钢具有高纯净度和良好的强度与塑韧性配合,其旋转弯曲疲劳试样的疲劳极限可达 730MPa;在较高应力下,裂纹起源于试样表面因加工刀痕和擦伤等引起的缺陷,且存在多处裂纹源。     

Wear Evolution in a Stranded Rope Subjected to Cyclic Bending

Wire ropes, due to their construction, combine two very interesting properties: high axial strength and flexibility in bending. However, the assemblage of wires to form flexible ropes results in the sliding of contacting wires and the creation of wear scars, which can act as stress risers and reduce the fatigue life of ropes. Therefore, in order to understand the fatigue behavior of wire ropes, the degradation that occurs between the wires and the strands has to be studied first. In this study, after identifying the main wear patterns for a polymer-covered stranded rope, the wear evolution along the number of cycles and the effect of the sheave diameter in the preferential wear sites were analyzed. The tests were carried out in a custom-made Bending over Sheave (BoS) fatigue test bench and short segments of the rope were analyzed by Scanning Electron Microscope (SEM) and confocal imaging profilometry in order to characterize the wear scars. The worn volume and the wear scar depth were selected as the most suitable parameters to characterize the wear behavior of wires. In addition, the importance of the polymeric cover and sheave diameter was proved: a reduction of the sheave diameter results in a bigger wear rate (μm³/cycle).     

表面纳米化对工业纯锆四点弯曲疲劳性能的影响

采用表面机械研磨工艺对工业纯锆进行处理,利用四点弯曲疲劳试验对试样的疲劳性能进行测试。通过对试样微观组织观察、显微硬度和残余应力表征,并结合有限元方法对四点弯曲试样应力分布的模拟,分析表面纳米化对工业纯锆四点弯曲疲劳性能的影响机理。研究表明,表面纳米化工业纯锆相对于原始试样疲劳极限提高约23%。这是由于原始工业纯锆在加载时最大拉应力位于试样表层,导致疲劳裂纹在表层萌生,而表面纳米化工业纯锆由于组织强化及残余压应力作用,使疲劳强度得到提高,并且使裂纹在次表层萌生,从而获得较好的疲劳性能。     

Effect of Current Pulses on Fatigue of Thin NiTi Wires for Shape Memory Actuators

Shape memory alloys (SMA) are used in many technological applications, thanks to their unique properties: superelasticity and shape memory (SM) effect. Many efforts have been made to improve performance of SMA wires to utilize them as thermal actuators also for many thousands of cycles. Near-equiatomic nickel-titanium compound is the most used materials for SM actuators because of its high recoverable values of strain and good cycling stability, if compared to the other known SMA. In this study, the functional properties of NiTi thin wires (80 μm) thermally cycled under a constant load (200 MPa) were investigated. In particular, the effect of two heating conditions, carried out by a step and a ramp current pulses, on functional fatigue of SMA has been studied. By means of an experimental apparatus, thermomechanical cycling, thermal loop under constant load and actuation time (AT) tests were carried out to investigate the alteration and the trend of recovered strain, irreversible strain, characteristic temperatures, and ATs of the thin SM wires.     

Mechanical properties of superconducting MgB2 wire

This study aims at examining the mechanical properties of MgB₂ wires fabricated with PIT method by studying the effect of tensile and bending stresses on their current carrying capacity. Wires are mounted on a tensile machine and are subjected to different load increments within both the elastic and the plastic regions. The current carrying capacity is measured for each load and the behavior of I_c versus stress/strain is studied. Microstructures of MgB₂ core are studied for different loads by using SEM. For bending tests, two cases are examined. The first case is to anneal MgB₂ wires then wind them on mandrels with different diameters, while the second case is to wind un-annealed wires on the same mandrels with different diameters then anneal the winded wires. A comparison between both cases is made using SEM for all different diameters and measuring the corresponding I_c. The behavior of I_c versus bending strain is studied. This whole study aims at giving a clear picture of the optimum loading, bending and processing conditions at which MgB₂ wires will possess a high current carrying capacity for practical applications.     

飞机操纵系统钢索断裂原因分析

某型飞机在飞行减速收油门时,发动机操纵钢索突然发生断裂失效,导致发动机停车。通过断口宏微观观察、化学成分分析、极限拉力测试及钢丝表面痕迹观察,并结合理论分析和疲劳试验对飞机操纵系统钢索进行了综合分析,探讨了操纵钢索发生断裂的原因。结果表明：钢索的断裂是以弯曲应力为主要控制因素的疲劳断裂,钢索与滑轮及钢丝与钢丝间的磨损促使了疲劳裂纹的萌生。通过改进滑轮与钢索的直径设计及改善钢索与滑轮槽接触面的润滑条件,提高了操纵系统的疲劳寿命。     

Fatigue response,fracture characteristic and life modeling of a near-alpha titanium alloy under typical cyclic loadings in service

Experimental investigations on the fatigue behavior of a near-alpha titanium alloy under typical cyclic loadings were carried out to simulate the service loading states applied on the engine blades.The axial stress-controlled tension–tension low-cycle fatigue(LCF) tests were carried out over a range of maximum stresses and stress ratios.The rotary bending tests were conducted using a step-loading procedure to reveal the high-cycle fatigue(HCF) limit stresses.The cyclic softening effect is observed in this material,and the strain ratcheting occurs obviously at the maximum LCF loading of 900 MPa.The LCF resistance is found to be dependent on both the maximum loading and the stress ratio.The HCF limit stresses for 1 9 107 and 1 9 106 cycles are determined as405.7 and 457.6 MPa,respectively.The macroscopic fatigue fracture mode and the failure features on fracture surfaces were analyzed by scanning electron microscope(SEM).     

焊趾TIG熔修对10Ni5CrMoV钢焊接接头弯曲疲劳性能的影响

采用悬臂弯曲疲劳试验方法比较了相同加载条件下焊趾TIG熔修与否的10Ni5CrMoV钢焊接接头的疲劳寿命．并对焊趾TIG熔修与否的焊接接头在加载条件下的应力应变场进行了有限元计算。结果表明TIG熔修对焊趾形状的改善作用能有效降低焊趾处的应力集中程度，明显提高10Ni5CrMoV钢焊接接头弯曲疲劳性能。     

Corrosion and fatigue in micro-sized Ni cantilever beams

The Ni microcantilevers were fabricated by femtosecond laser. The corrosion behavior of the micro-sized Ni cantilever beams was studied by electrochemical noise and a newly developed fatigue testing method. The results show that the micro-sized specimens exhibit general corrosion behavior under the studied corrosion condition, whereas the ordinary-sized plates exhibit the localized corrosion behavior. The critical load amplitude of the micro-sized Ni specimens under corrosion fatigue status was determined to be 15 mN. The maximum bending loads, which were measured by fatigue tests, decrease gradually prior to final fracture. Corrosion fracture first occurs in the range of notch with a higher tensile bending stress, and exhibits clear evidence of trans-columnar fracture. The variation of maximum bending loads with time agrees with that creep deformation of the micro-sized Ni specimens can easily occur at room temperature, which implies that the micro-sized Ni specimens appear to have an improved resistance towards total crack as compared with the ordinary-sized Ni specimens.