纳米压痕法测量经深冷处理后铝青铜的硬度和弹性模量

借助纳米力学测试系统测试经深冷处理后铝青铜的硬度和弹性模量。结果表明:深冷处理后铝青铜的硬度和弹性模量分别为3.82GPa和117.67GPa,且铝青铜的硬度随压入深度的增加而逐渐降低,反映出硬度存在的尺寸效应,但弹性模量不存在尺寸效应现象。     

Multibody dynamic modeling of five-axis machine tool vibrations and controller

A computationally efficient, reduced-order multibody dynamic model of a five-axis machine tool is presented. The machine tool is modeled by substructures assembled via flexible springs and damping elements at interfaces which affect the machining performance. NC tool path commands are processed by the linear acceleration-based motion trajectory filters and fed to the axis servo controllers through an inverse kinematic model of the machine. The computed motor torque commands are applied to the structural dynamic model of the machine at the motor connections. The experimentally validated model predicts the performance of the five-axis CNC machine's controller along the tool path.     

Oxidation resistance of nanocrystalline vis-à-vis microcrystalline Fe-Cr alloys

This paper investigates the hypothesis that nanocrystalline structure may confer considerable oxidation resistance to iron-chromium alloys at much lower chromium contents. Discs of nanocrystalline Fe-10%Cr alloy were produced by ball milling of Fe and Cr powders and compaction of the powder without considerable grain growth (by processing within a suitable time-temperature window). Corrosion resistance of discs of nanocrystalline and microcrystalline alloys was compared by subjecting them to oxidation in air and post-oxidation characterisation of the oxide scales by secondary ion mass spectroscopy (SIMS). Nanocrystalline Fe-10%Cr alloy showed considerably greater oxidation resistance than the microcrystalline alloy of the same composition. Chromium content of the inner scale formed over the nanocrystalline alloy was detected to be nearly five times greater than that in the case of microcrystalline alloy, facilitating formation of the passive layer and providing an explanation for the greater oxidation of the former.     

Characterization of the in-situ non-linear shear response of laminated fiber-reinforced composites

A simple procedure to determine the non-linear in-plane lamina shear response of laminated composites is presented. Using the ±45° symmetric laminate tensile test results, in conjunction with computational micromechanics, a method was developed and validated to characterize the lamina shear response and the in-situ matrix shear response. Load, and axial and transverse strains measured in the tests were used to calculate the non-linear shear stress–shear strain response of the composite. From this result, the in-situ matrix equivalent stress–strain response was obtained, with some simplifying assumptions, and subsequently used in a micromechanics-based representative finite element (FE) model of the ±45° symmetric laminate tensile test to determine the accuracy of the non-linear response of the in-situ matrix. Results from the FE model of a representative cell (RC) that depicts fiber diameter, fiber volume fraction (V_f) and angled fiber packing of the ±45° symmetric laminate were found to match the tests result well. Thus, the procedure to extract the non-linear lamina shear response and the non-linear in-situ matrix response from the ±45° symmetric laminate tensile test was validated.     

Hybrid CFRP/titanium bolted joints: Performance assessment and application to a spacecraft payload adaptor

This paper presents an experimental investigation of the mechanical response and the industrial manufacturability of CFRP–titanium hybrid laminates using the example of a spacecraft payload adaptor. The local hybridization with metal within a bolted joint region of composite laminates is proven to be an effective method of increasing the mechanical joint efficiency of highly loaded bolted joints. High-strength titanium foils are locally embedded into the composite laminate by means of ply substitution techniques, thus avoiding any local laminate thickening and providing for a local laminate with high bearing and shear capabilities. An extensive sample and component test program has been performed evaluating the impact of different design parameters and load conditions. The verification of the hybrid technique’s processability, inspectability and compatibility with a standard industrial fibre placement process has been successfully demonstrated through the manufacturing of a spacecraft payload adaptor featuring diverse applications of the hybridization technique.     

An examination of small fatigue crack morphology

Test results for the growth of a small corner crack under cyclic loading are presented. The number of grains that are crossed by the crack front ranges from about three to ten during the crack advance. Crack path profile measurements on the adjacent corner faces are presented. Also, a microscopic examination of the crack path morphology of a polished and etched surface that is adjacent to the corner reveals the presence of complex branching mechanisms, and localized regions of intensive damage. Examination of sub-surfaces reveals that though branching and localized damage are present, they diminish with increasing depth of the subsurface. It is concluded that during early growth, the crack surface deviates substantially from an idealized planar surface model, and that Modes I, II, and III are all operative.