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通过纳米压痕、微压痕和微划痕试验,研究了单晶MgO不同晶面的的纳米力学性能以及微观变形和损伤特征。根据加载条件的不同,单晶MgO会发生:弹性变形、弹塑性变形、蠕变变形、微裂纹和微破碎。弹性变形时的纳米压痕力-位移曲线符合赫兹弹性接触理论,其变形在卸载后可完全恢复;塑性变形时MgO在{110}易滑移晶面系内位错形核和滑移的结果。 相似文献
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利用紧凑拉伸(CT)试样对水下高压气瓶用钢37CrNi3MoVE材料在模拟海水环境中进行了应力腐蚀试验研究,采用恒位移速率控制,试样为平面应力试样,获得了不同位移速率下载荷一位移曲线和裂纹扩展速率与应力强度因子关系曲线.结果表明,载荷与裂纹扩展速率增长趋势与加载速率密切相关,位移速率为5.0×10-5 mm/s比1.0×10-5 mm/s时裂纹扩展前期的最大载荷高12.73%,裂纹扩展约2 mm后,相同裂纹长度下能承受的载荷基本一致;该材料在海水环境中,平面应力状态下,裂纹起始扩展应力强度因子约110 MPa√m.位移速率为1.0×10-5 mm/s和3.0×10-5mm/s时测得的裂纹扩展速率da/ dt分别出现2.9×10-5 mm/s和8.2×10-5 mm/s的稳定扩展阶段,但位移速率为5.0×10-5 mm/s时,da/dt与KI的关系曲线没有明显稳定扩展阶段.位移速率低者比位移速率高的应力腐蚀明显. 相似文献
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残余应力的存在直接影响材料的力学性能,在压痕法中影响其压痕形状大小、压入载荷-位移曲线和隆起量,因此通过比较压痕形状大小、压入载荷-位移曲线和隆起量的大小,可以推断出构件内部残余应力,再通过有限元研究不同程度的残余应力对压痕形状、压入载荷-位移曲线和隆起量的影响.研究结果表明, 残余压应力使压痕尺寸变小,残余拉应力使压痕尺寸变大,不同性质和大小分布的残余应力使压痕形状为椭圆形,压入载荷-位移曲线斜率和隆起量高度随着残余压应力的增加而增加,随着拉应力的减小而减小,当构件内部存在一定程度的残余拉应力时,随着压入载荷的继续增加出现负隆起量(沉降量),沉降量的大小与压入载荷的大小和残余拉应力的程度有关. 相似文献
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采用激光位移传感器对开孔圆柱壳的三维形貌进行测量,基于实测数据建立有限元模型,利用ABAQUS对不同开孔率的圆柱壳进行非线性有限元分析,模拟结果显示:载荷位移曲线先线性增大,后出现突变,轴向压力迅速减小,轴压屈曲临界载荷随着开孔率增大而减小。对开孔率为5%,10%,15%的圆柱壳进行轴压屈曲试验,试验采用液压装置进行轴压,轴压数据通过称重传感器获得。对轴压屈曲临界载荷模拟值与试验值进行比较,最小的相对误差只有10.8%。说明运用激光扫描法建模进行非线性有限元分析,可以较好地预测开孔圆柱壳轴压屈曲临界载荷。 相似文献
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Murugavel Rathinam 《Journal of Mechanical Science and Technology》2010,24(11):2241-2245
The temperature response on the properties of single crystal gold (111) plane at elevated temperatures was considered in this
work. The ability to perform nanoindentation experiments at elevated temperatures opens up significant new possibilities in
nanotechnology. The experiments are performed at various temperatures of 373 K, 473 K and 573 K with tailor made Berkovitch
tip of radius 100 nm to study the behavior of single crystal gold. The new phenomenon of material bouncing back under the
indenter at the end of unloading was clearly noted, due to the accumulation of high energy. The results for different temperatures
were compared. Our experiments clearly show the onset of the first burst of dislocation glide, which is indicated by a sudden
increase of displacement with no increase of loading, the onset of plastic deformation in connection with the periodic bursts,
and the strain hardening, softening and release effects. Pile up was also observed. The complete elastic range was found.
There was significant drop in the hardness, elastic modulus and the increase in depth with increasing temperature. The elastic
recovery was reduced at higher temperatures. 相似文献
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A theoretical model is developed to study the effect of dwell time on the junction growth and static friction of a creeping
polymer sphere in contact with a rigid flat under full stick contact condition. A rapid normal loading into the elastic–plastic
contact regime is followed by a rest period during which creep takes place causing contact area growth, and stress relaxation
that can completely eliminate the plastic zone in the sphere. At the end of this rest time, an increasing tangential loading
is applied to the flat till sliding inception occurs. During this loading step, further increase of the contact area and reappearing
of a plastic zone in the sphere take place. An increase in static friction resulting from the dwell time during the creep
stage is clearly demonstrated and explained. 相似文献
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分析电阻应变式传感器蠕变特性,利用其加/卸载和蠕变输出变化率的不同,判断蠕变起始点,根据蠕变过程和零点变化的特点进行蠕变跟踪,以此确定传感器实际载荷。此方法简单方便,易于实现。 相似文献
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Dynamic mechanical contacts with nanometer-to-micrometer dimensions are important in scanned probe microscopy, ultra-low load indentation, microelectromechanical systems, compact discs, etc. The response of these contacts is poorly understood if they involve adhesive viscoelastic materials, such as polymers and self-assembled monolayers. We have studied dynamic contacts to styrene–butadiene latex films. Plots of load vs. displacement show substantial adhesion hysteresis between the loading and unloading portions. The hysteresis is at least partially due to creep, as indicated by the continued increase in penetration after the start of unloading. Thermodynamic works of adhesion were estimated from fits to the loading–unloading data obtained at small loading and unloading rates. Theoretical models that include adhesion but neglect long-range creep effects could not fit the data at all loading rates. Creep tests were carried out under constant load. A model due to Hui, Baney, and Kramer (HBK), which predicts the response of an adhesive viscoelastic contact under increasing load, was used to extract a mode I stress-intensity functional from the data. When this functional is normalized by the square root of the displacement rate, it is shown empirically, to have a simple, nearly universal time-dependence. Variations of this universal form due to load, range of interaction potential, glass transition temperature, and probe shape are weak. This result supports the suggestion of HBK that the stress-intensity functional provides a useful way to characterize adhesive contacts to viscoelastic materials. 相似文献
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ZHOU Liang YAOYingxue 《机械工程学报》2006,(Z1)
针对材料纳米压痕硬度的压痕尺寸效应(Indentation size effect,ISE),利用纳米压痕技术测得单晶铝和单晶硅的载荷-压深曲线,获得最大载荷和最大压深,并结合原子力显微镜,获得压痕的三维形貌,计算出压痕的真实残余面积。根据最大压深和残余面积提出了一个新的模型——残余面积最大压深模型,此模型能更好地理解和描述材料硬度的压痕尺寸效应,并与其他几种典型的理论和模型进行了比较和分析。 相似文献
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《Tribology - Materials, Surfaces & Interfaces》2013,7(4):219-224
AbstractThe bound model to determine coating toughness limits by nanoindentation tests was originally proposed by Toonder et al. However, the assumptions in this method conflict with each other. It provides lower and upper toughness limits for load control tests; however, it is unable to give the lower toughness limit for displacement control tests. In this paper, a modified model is presented by more comprehensive analysis of the unloading curves at the points where the crack starts and stops respectively. This modified method equally provides the lower and upper limits of fracture dissipated energy for both load control and displacement control. The model developed here has been successfully applied to fullerene like CNx coatings deposited on various substrates such as Si, SiC and Al2O3. It is also applicable to other coated systems provided that the through thickness fracture induced excursion is observed in the load–displacement curve. 相似文献
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A nano-fretting test technique has been recently developed to enable the in situ study of wear at the micro- and nano-scale. It has been used to study the small scale wear of Si(1 0 0) using a 4.6 μm spheroconical indenter as test probe over the applied load range 30-300 mN. Contact damage assessment by in situ measurements of probe displacement were supplemented by post-test SEM imaging and wear scar analysis by confocal microscopy. The wear behaviour was dependent on the rate of initial loading. When the load was applied abruptly (<0.3 s), radial and lateral cracking and material removal was observed and large displacement jumps (pop-ins) were observed during the subsequent 1000 s constant load nano-fretting test. The crack morphology was very similar to that in repetitive nano-impact tests and conventional nanoindentation at higher applied load with the same probe. In contrast, when the load was applied more slowly (10 s) radial cracking was not observed and there was a distinct threshold load (∼100 mN) marking the transition to a more severe wear mode with extensive lateral cracking and material removal. 相似文献
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为了研究火箭发动机法兰系统载荷-变形随时间的变化,将其作为一个整体,考虑系统中各元件的蠕变-松弛作用,提出了在预紧和操作情况下,计算法兰系统载荷-变形的新方法;算例计算结果表明:在预紧情况下的很长时间段内,螺栓应力和O形圈应力下降得非常缓慢;在操作情况下的开始时间段内,其下降较快,随着时间的推移,下降速率逐渐减慢。在预紧情况下,法兰系统各元件材料的蠕变-松弛性能对O形圈应力的影响较小;在操作情况下,这种影响则较大。若考虑螺栓的蠕变-松弛,则随螺栓蠕变-松弛系数的增大,螺栓应力和O形圈应力随时间下降得较多。 相似文献
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Murugavel Rathinam Ramesh Thillaigovindan Prema Paramasivam 《Journal of Mechanical Science and Technology》2009,23(10):2652-2657
High temperatures generally affect materials in some form. In this regard, the capability to perform nanoscale measurements
at elevated temperatures opens up new possibilities for investigating the temperature dependence of materials’ mechanical
properties. Particularly, the responses of aluminum’s different mechanical properties to indentation at various temperatures
have been studied experimentally. In this paper, aluminum response to different room temperatures was examined. The behaviors
of a single crystal aluminum during loading and unloading were observed. Nanoindentation experiments on a single crystal aluminum
(100) sample at temperatures of 265 K and 388 K were performed with different loading conditions. At the start of the first
burst of the dislocation glide, which was indicated by a sudden increase in displacement with no increase in loading, evidence
of plastic properties and softening effects on aluminum was identified. The ductile to brittle transition was observed at
temperatures below 273 K. Generally, there was a significant increase in the penetration depth and a decrease in hardness,
elastic modulus, and elastic recovery as the testing temperature increased. 相似文献
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Lu Z McKellop HA 《Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine》2011,225(8):809-820
Polymers such as polymethyl-methacrylate (PMMA) surgical cement undergo elastic and viscoelastic deformation (creep) in response to physiological cyclic loading. Theoretically, the effect of gradual creep deformation on the stresses, strains, and displacements of a prosthetic joint can be evaluated by running a finite element analysis (FEA) model through a large number of loading cycles. However, with complex (i.e. realistic) models, this approach may require extensive computational time, and may accumulate unacceptably large numerical errors over the many iterations of the model. The present study utilized a Fourier series to represent a periodic stress and incorporated it in the linear viscoelastic constitutive equation. It was demonstrated that, for a linear viscoelastic material, the time average (i.e. the constant in the Fourier series) of the cyclic stress determined the accumulated creep strain and the sinusoidal components of the stress produced the periodic creep strain with a zero average and negligible amplitude. For a geometrically linear FEA model, the solution based on a cyclic stress can be readily applied to an external cyclic load, that is, the creep strain is determined by the time average of the cyclic load. While femoral component models were considered as geometrically non-linear, an FEA model of a femur implanted with an Exeter hip prosthesis showed that there was only a minor difference between the profile of the applied sinusoidal load and that of the resulting displacement. In such cases, applying the time average of a cyclic load to calculate the resulting creep strain with a given duration of loading should expect to provide acceptable accuracy, with a marked reduction in the computational time. 相似文献