冲击压缩下铝、铜、钨的剪切模量和屈服强度与压力和温度的相关性

对铝、铜和钨在冲击压缩状态下的剪切模量和屈服强度的实验数据进行了综合分析,并与St einberg-Cochran-Guinan(SCG)模型的计算结果进行了比较,结果表明,铝在50 GPa、铜在1 00 GPa、钨在200 GPa冲击压力以内,三种材料的剪切模量和屈服强度随温度和压力的变化 趋势基本相似,即SCG模型的假设Y′_pY₀=G′_pG ₀,Y′_TY₀=G′_TG₀对这三种材料在上述冲击压力范围内近似成立,利用该模型可以较好地描述材料在冲击压缩 下的本构行为.关键词：剪切模量屈服强度压力温度     

高温高压下材料的本构模型

 在SCG模型基础上对其温度软化效应项作了改进,所提出的新模型在熔点温度T_m处满足剪切模量G(T_m)=0,从而提高了温度的适用范围。对Al和93W作了计算,其理论结果与实验符合相当好。     

The aging of atmospheric plasma-treated ultrahigh-modulus polyethylene fibers

The aging effects of atmospheric plasma treatments on UHMPE fibers are studied. UHMPE fibers are treated for 0.5 and 1 min with He/O₂/air gas and for 2 and 4 min with He/air gas by atmospheric pressure plasma on a capacitively coupled device at a frequency of 5 kHz. The samples are tested for fiber/epoxy interfacial shear strength at time intervals of 0, 3, 15 and 30 days after initial plasma treatment. Scanning electron microscopy shows micro-cracks on each set of treated fibers, which is not affected by aging over the 30 day study. Interfacial shear strengths (IFSS) for plasma-treated fibers are 2–3 times as high as that of the control. The IFSS for the plasma treated fibers remains constant up to 15 days and then decreases afterwards. XPS Analysis shows a slight increase in atomic concentration of oxygen and nitrogen for each plasma-treated sample. For the He/O₂/air plasma-treated samples, XPS analysis shows an observable increase in C–OH bonds, C=O bonds and COOH bonds, while for the He/air plasma-treated samples, there is a slight increase in C–OH and O=C–O bonds. After 30 days, a decrease in oxygen content for all plasma-treated samples is manifested.     

多晶薄膜屈服强度的一个模型

从位错运动的应力功和应变能关系导出了附着在基体上并有钝化层薄膜的屈服强度公式.该式表明多晶薄膜的屈服强度由两个影响因子（晶粒取向和位错类型）和三个强化因子（钝化层强化,基体强化和晶粒强化）确定.和已报道的实验结果基本一致表明了该模型的合理性.关键词：多晶薄膜屈服强度     

Failure waves in glass under dynamic compression

Abstract

Plate impact (I-d strain) and bar impact (I-d stress) experiments were performed on soda lime glass and pyrex glass. Embedded manganin gauges were used to monitor stress-time profiles in both types of experiments. In the plate impact experiments we found that glass not only fails through inelastic (or densification) deformation, but also through a unique failure process which gives rise to a failure wave first observed by Kanel et al. in the Soviet Union in 1990. In the present work three independent observations were made that support the existence of failure wave in glass: (i) the spall strength below and above the HEL is zero behind the failure wave, (ii) a small recompression is present in the longitudinal gauge (embedded between glass and PMMA) profile due to the reflections of release waves from the advancing failure wave, and (iii) transverse stress (measured by transverse gauge) increases on the arrival of the failure wave. The transverse stress increases because the glass loses its shear strength as a result of the arrival of the failure wave. The speed of the failure wave is about 1.5–2mm/μs. In the experiments on pyrex bars we used high speed Imacon framing camera to monitor the speed of the failure front. We found that pyrex bars fail through a failure front propagating across the cross section of the bar. The speed of the failure front is a function of the impactor (pyrex bar or steel plate) velocity. The speed increases from 2.3 mm/μs, corresponding to impact velocity of 125 m/s, to 5.2mm/μs for impact velocity of 330 m/s.     

The effect of the microstructure of porous alumina films on the mechanical properties of glass-fiber-reinforced aluminum laminates

The glass-fiber-reinforced aluminum laminates were obtained by anodizing aluminum alloy under anodizing voltage of 10, 20, and 30?V in the 200?g/L H₃PO₄ electrolyte. Scanning electron microscopy (SEM), short beam, and tensile tests were employed to determine the surface morphology, interlaminar shear strength (ILSS) and tensile strength of laminates, respectively. The results also show that the epoxy penetrates into the pores of the anodic films, and this is the mechanism of adhesion. The ILSS and tensile strength of the anodized specimens (under 20?V) respectively increased by approximately 50 and 15% comparing with those of the non-anodized specimens. This increase of mechanical properties results from the porous surface of aluminum providing greater mechanical interlocking to epoxy. The ILSS and tensile strengths of the anodized specimens increased with the increase of anodizing voltage from 10 to 20?V; however, it decreased when the voltage further increased to 30?V. It is considered that the microstructure evolution of the porous films has a significant effect on the mechanical properties of the laminates.     

Relation between interfacial shear strength and compressive strength of carbon fiber/epoxy resin composite strands

The mechanism with which the fiber-matrix interfacial strength exerts its influence on the compressive strength of fiber reinforced composites has been studied by measuring the axial compressive strength of carbon fiber/epoxy resin unidirectional composite strands having different levels of interfacial shear strength. The composite strands are used for experiments in order to investigate the compressive strength which is not affected by the delamination taking place at a weak interlayer of the laminated composites. The interfacial strength is varied by applying various degrees of liquid-phase surface treatment to the fibers. The efficiency of the compressive strength of the fibers utilized in the strength of the composite strands is estimated by measuring the compressive strength of the single carbon filaments with a micro-compression test. The compressive strength of the composite strands does not increase monotonically with increasing interfacial shear strength but showes lower values at higher interfacial shear strengths. With increasing interfacial shear strength, the suppression of the interfacial failure in the misaligned fiber region increases the compressive strength, while at higher interfacial shear strengths, the enhancement of the crack sensitivity decreases the compressive strength.     

Effects of severe-strain-induced defects on the mechanical response of two kinds of high-angle grain boundaries

ABSTRACT

Grain boundaries of metallic materials subjected to severe plastic deformation exhibit significantly enhanced diffusivity and excess energy compared with their relaxed poly- or bi-crystalline counterparts even when the macroscopic degrees of freedom are the same in both types of grain boundaries. Boundaries of excess energy are/can be relaxed by annealing. As a first step in accounting for this experimentally observed high-energy state of general high-angle grain boundaries subjected to severe plastic deformation, a concept of localised basic shear units and the presence of localised extra free volume in these units situated in different locations in the grain boundaries, which was originally proposed to explain steady-state structural superplastic flow, is made use of. Using MD simulation, the mechanical response of these modified grain boundaries is compared with that of their relaxed state. The results are also compared with a case of a homogeneous distribution of extra free volume within the grain boundary. The localised shear units containing extra free volume introduced in the grain boundaries are found to alter their physical and mechanical features strongly, which, in turn, drastically affect, consistent with experimental results, the mechanical response of the heavily deformed material.     

Wedge plate interferometry: a new dual field configuration for collimation testing

A method of deriving a dual field fringe pattern from a single wedge plate for collimation testing is presented. The proposed technique uses a wedge plate and a 90° prism retroreflector to form two interference fields. With the two sets of fringes, the technique provides twofold increase in sensitivity and has its own reference.     

惯性约束聚变实验用玻璃微球堵口特种胶研究

通过对不同固化和热处理过程后的胶粘剂的剪切强度、表面形貌特征、热性能的研究,分析了增韧剂和偶联剂对环氧有机硅胶粘剂性能的影响。研究表明：随着增韧剂含量的增加,胶粘剂热分解温度下降;增韧剂质量分数为25%时,有机硅与环氧树脂相容性较好,制备的胶粘剂综合性能较好;硅烷偶联剂能改善胶层与金属界面的胶接强度,提高环氧有机硅胶粘剂的拉伸剪切强度。显微组织观察分析表明,环氧有机硅胶粘剂中环氧树脂分子链与有机硅高分子链处于一定微相分离状态。     

Yield strength of attached copper film

Variation of stress in attached copper film with an applied strain is measured by X-ray diffraction combined with a four-point bending method.A lower slope of the initial elastic segment of the curve of X-ray measured stress versus applied strain results from incomplete elastic strain transferred from the substrate to the film due to insufficiently strong interface cohesion.So the slope of the initial elastic segment of the X-ray stress (or X-ray strain directly) of the film against the substrate applied strain may be used to measure the film-substrate cohesive strength.The yield strength of the attached copper film is much higher than that of the bulk material and varies linearly with the inverse of the film thickness.     

Digital image correlation approach to cracking and decohesion in a brittle coating/ductile substrate system

By using a digital image correlation technique, the full/local field strain in a brittle coating/ductile substrate system during tension has been successfully monitored. One of the most important experimental results indicates that the distribution of interfacial shear stress in the segmented coating is antisymmetric about the center, which clarifies several controversial assumptions introduced in theoretical models. Two key mechanical properties of thermal barrier coatings, fracture strength in coating and interfacial adhesion strength, were determined as 35.0 ± 4.6 and 14.1 ± 3.2 MPa, respectively, which are consistent with available experimental data.     

冲击加载下LY12铝合金的动态屈服强度和层裂强度与温度的相关性

采用可测量任意反射表面的速度干涉仪对LY12铝合金在不同初始温度条件下的动态屈服与层裂行为进行了实验研究,温度范围从室温到接近熔化温度.实验结果显示：LY12铝合金的动态屈服强度随着温度升高而快速下降,当初始温度为847K (比熔化温度低86K) 时,其屈服强度仅为室温下的15％,层裂强度也随着温度升高而减小,在296—847K的实验温度范围内,层裂强度损失80%.通过实验结果与模型估算值的比较,发现Zerilli-Armstrong (ZA) 模型可以对LY12铝合金的动态屈服强度与温度的相关性进行较好关键词：温度相关性LY12铝合金动态屈服强度层裂强度     

Contributions of different strengthening mechanisms to the shear strength of an extruded Mg–4Zn–0.5Ca alloy

The shear deformation behaviour of an extruded Mg–4Zn–0.5Ca alloy was studied using shear punch testing at room temperature. The extrusion process effectively refined the microstructure, leading to a grain size of 4.6 ± 1.4 μm. Contributions of different strengthening mechanisms to the room temperature shear yield stress, and overall flow stress of the material, were calculated. These mechanisms include dislocation strengthening, grain boundary strengthening, solid solution hardening and strengthening resulting from second-phase particles. Grain boundary strengthening and solid solution hardening made significant contributions to the overall strength of the material, while the contributions of second-phase particles and dislocations were trivial. The observed differences between calculated and experimental strength values were discussed based on the textural softening of the material.     

The Role of Intra-Yarn Shear in Integrated Multi-Scale Deformation Analyses of Woven Fabrics: A Critical Review

This article attempts to bring an enhanced insight into the analysis of in-plane shear behavior of woven fabrics. Two common methods have been used to characterize the shear behavior of woven preforms, namely the Bias Extension (BE) and Picture Frame (PF) tests. In spite of the identical macro-scale shear deformation of fabrics in these two characterization procedures, the current study demonstrates that their underlying micro- and meso-scale deformation mechanisms are quite distinct. The trellising mechanism, which is based on the well-known Pin-Joint Theory (PJT), has been regarded for a long time as the sole model to describe the meso-scale deformation of woven fabrics in both the BE and PF tests. Throughout this article, this mechanism is challenged for the PF test by undertaking a multi-scale analysis along with a critical review and integration of the previous experimental, analytical, and numerical studies. Intra-yarn shear, which has not been fully understood yet, is substantiated as a potential meso-level deformation mechanism occurring in the PF test. Accordingly, a new meso-level deformation model is proposed and compared with the trellising shear pattern in the BE setup. Afterward, the comparison is extended from meso-level to macro-level in order to provide more in-depth hypotheses for explaining differences reported in the literature between the shear characteristics of fabrics using BE and PF tests. Finally, some guidelines have been sought to select more reliable characterization method given a forming process.     

Yield strengths and stress induced crackles in copper films：effects of substrate and passivated layer

Yield strengths in unpassivated and 530 nm TiN passivated Cu films deposited on Ti, high-speed steel and Ni substrates have been measured by x-ray diffraction (XRD) in combination with the four-point bending method. The results show that, although the texture and average grain size, investigated by XRD and transmission electron microscopy respectively, do not vary with different substrate, the yield strength of the Cu film increases obviously when a thin passivated layer is present and varies slightly with substrates. Many crackles appear in the passivated Cu film on Ti substrate but do not appear in other samples. The experimental results have been explained satisfactorily with an expression for the yield strength of thin films given previously.     

The gamma irradiation of PBO fiber on the mechanical and tribological properties of PTFE composites

The mechanical and tribological behavior of gamma irradiated poly(p-phenylene benzobisoxazole) (PBO) fiber filled polytetrafluoroethylene (PTFE) composites was investigated. The gamma irradiated PBO fiber composite had the highest inter-laminar shear strength value of all the combinations because its higher bond strength may have hindered a large fiber/matrix debonding. X-ray photoelectron spectroscopy results indicate that the contents of polar groups on the surface of gamma irradiated PBO fiber increase compared to PBO fiber. The wear tests were conducted on a ring-on-block apparatus using composite block against polished metal counterparts under dry sliding conditions. It can also be found that gamma irradiation treatment was helpful to the improvement of the anti-wear ability of the PTFE composite which was related to the abrasive wear mechanism.     

Improvement of surface wettability and interfacial adhesion of poly-(p-phenylene terephthalamide) by incorporation of the polyamide benzimidazole segment

In order to investigate the effect of the polyamide benzimidazole group on the surface wettability and interfacial adhesion of fiber/matrix composites, surface features of two kinds of aramid fibers, poly (p-phenylene terephthalamide) fiber (Kevlar-49) and poly-(polyamide benzimidazole-co-p-phenylene terephthalamide) (DAFIII), have been analyzed by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and contact angle analysis (CAA) system, respectively.The results show that with the incorporation of the polyamide benzimidazole segment, more polar functional groups exist on DAFIII surface. The contact angles of water and diiodomethane on DAFIII surface get smaller. The surface free energy of DAFIII increases to 36.5 mJ/m², which is 2.3% higher than that of Kevlar-49. In addition, DAFIII has a larger rough surface compared with that of Kevlar-49 due to different spinning processes. The interfacial shear strength (IFSS) of DAFIII/matrix composite is 25.7% higher than that of Kevlar-49/matrix composite, in agreement with the observed results from surface feature tests. SEM micrographs of failed micro-droplet specimens reveal a strong correlation between the fracture features and the observed test data.