Use of thin adherends in adhesively bonded joints under different loading modes

Abstract

The adhesive bonding technique is especially suited to the joining of thin materials. An adhesive joint consists of a structural adhesive and an adherend. When designing the joint, focusing on the behaviour of the adhesive is important. However, if the material to be joined is thin, then it becomes much more important to concentrate on the material properties. In the present work, two adhesives with different mechanical behaviour and two thin adherend materials, steel and aluminium, were selected for the production of adhesive joints. The single lap joint configuration was subjected to tests under bending load and also under tensile load. The results show that adherend plasticity plays an important part in the joint failure; specimens under bending load experienced high plastic deformation of adherends, depending on the strength of the adherend material. Overlap increase did not seem to affect the joint strength. When the joints were tested under tensile loading, it was observed that the load bearing capacity of adhesives was an important parameter influencing the joint strength, and that an increase in overlap seemed to contribute to the joint performance. In general, the results obtained imply that it is vital that the adherends used remain in their elastic deformation region to obtain a joint strength that reflects the mechanical behaviour of the adhesive used.     

Predictive quality control of hybrid metal-CFRP components using information fusion

The paper presents an approach to determine the durability of hybrid metal-CFRP components combining the results of non-destructive testing (ndt) and finite element simulation The advantage of hybrid metal-CFRP components lies in the use of the properties of the materials used. CFRP parts with higher specific stiffness and strength are combined with metallic joining points, so that established joining processes for metal components can be applied to these lightweight components. In order to further promote the use of these hybrids in industry, it is necessary to guarantee a high level of component reliability through 100% quality control in order to avoid production-related defects. These defects such as delamination or fibre disorientation however vary in shape, size and position and lead to different effects on the part performance and reliability. Therefore the presented approach includes the application of non-destructive testing methods that are applied as in-line quality control measures in order to determine defect characteristics of the inspected parts. Due to the novelty of the component under test it is necessary to evaluate the individual criticality of detected defects and how they affect part performance during the testing procedure. Therefore the acquired ndt-data is used in finite element simulations where defect characteristics are added to the component model and whose effects on part reliability are evaluated. The generation of additional information combining non-destructive testing and simulation is referred to as data fusion. In order to evaluate the validity of the presented approach the determined part performances are compared to experimental mechanic tests.     

汽车车身铝合金连接构件的拉伸试验分析

铝合金板在汽车车身中有着广泛的应用,对6082-T6铝合金在3种连接工艺下的拉伸强度进行了试验研究。首先,对比了自冲铆接连接工艺(SPR)下单铆、双铆、三铆的连接强度;并进一步对比了自冲铆接(SPR)、热融自攻丝铆接(FDS)和点焊(RSW)3种连接工艺的结构件的单铆的连接强度。利用MTS810型液压万能试验机结合图像相关技术(DIC)对上述铆接形式的试件进行拉伸试验,研究3种连接形式的强度与可靠性。通过SPR连接形式下的单铆、双铆和三铆试件的试验结果对比可知:双铆试件能够充分发挥铝合金材料性能,对采用SPR铆接形式的产品的安全设计有重要意义。通过对3种连接形式的单铆对比发现:SPR连接工艺的承载能力好、可靠性高。该试验结果可以指导汽车工艺的选择和优化。     

Effects of tensile test parameters on the mechanical properties of a bimodal Al–Mg alloy

The properties of aluminum alloy (AA) 5083 are shown to be significantly improved by grain size reduction through cryomilling and the incorporation of unmilled Al particles into the material, creating a bimodal grain size distribution consisting of coarse grains in a nanocrystalline matrix. To provide insight into the mechanical behavior and ultimately facilitate engineering applications, the present study reports on the effects of coarse grain ratio, anisotropy, strain rate and specimen size on the elastic–plastic behavior of bimodal AA 5083 evaluated in uniaxial tension tests using a full-factorial experiment design. To determine the governing failure mechanisms under different testing conditions, the specimens’ failure surfaces were analyzed using optical and electron microscopy. The results of the tests were found to conform to Joshi’s plasticity model. Significant anisotropy effects were observed, in a drastic reduction in strength and ductility, when tension was applied perpendicular (transverse) to the direction of extrusion. These specimens also exhibited a smooth, flat fracture surface morphology with a significantly different surface texture than specimens tested in the axial direction. It was found that decreasing specimen thickness and strain rate served to increase both the strength and ductility of the material. The failure surface morphology was found to differ between specimens of different thicknesses.     

Numerical Analysis of Sample-Size Effect on Strength of Alumina

Statistical characteristics of strength distribution in ceramic components should be clarified because of large scatter in ceramics strength. Characteristics of strength distribution, however, depend on sample size, i.e., the number of tested specimens. In this study, a numerical procedure in the framework of fracture mechanics was developed to estimate strength distribution of ceramics by assuming the same statistical distribution of cracks in a material. Experimental results in four-point bending tests of alumina, which were reported in a previous work, were cited to verify the validity of the developed procedure. Smooth specimens of distinct sizes as well as notched specimens with different notch shapes were used in the experiment. Monte Carlo simulations using the developed procedure were carried out to investigate effects of the sample size on strength properties of alumina specimens with various shapes. The simulated result revealed that the experimental strength for various types of specimens was almost covered within a range of upper and lower bounds of strength simulated for the alumina. The experimental mean strength correlated with the effective volume was also included in a band range between the maximum and the minimum of mean strength obtained by the simulation.     

Hydrogen embrittlement susceptibility and permeability of two ultra-high strength steels

Slow displacement rate tensile tests were carried out in a saturated H₂S solution to investigate the effect of hydrogen embrittlement on notched tensile strength (NTS) and fracture characteristics of two ultra-high strength steels (PH 13-8 Mo stainless steel and T-200 maraging steel). Hydrogen permeation properties were determined by an electrochemical permeation method. The results of permeation tests indicated that over-aged specimens showed a lower diffusivity/hydrogen flux and higher solubility than those solution-annealed. The great increase in reverted austenite (irreversible hydrogen traps) together with numerous precipitates at the expense of dislocations (reversible) in the over-aged specimen led to such a change in permeability. Ordinary tensile tests indicated that four tested specimens had roughly the same yield strength level. Hence, the hydrogen embrittlement susceptibility of the material could be related to their permeation properties. The uniform distribution of strong hydrogen traps in over-aged specimens instead of weak traps in the solution-annealed impeded the hydrogen transport toward the strained region, thus, the resistance to sulfide stress corrosion cracking was improved in over-aged specimens.     

Back Matter

Abstract

This paper is concerned with the experimental determination of thermomechanical properties of a cold box sand, which have a strong influence during the solidification in a sand casting process. To this end, the uniaxial behaviour for different temperatures up to the casting temperature of an aluminium alloy is investigated. For the tests at room temperature, the authors use optical measurement equipment, which is ideally suited to measure inhomogeneous deformations and strains within the material specimens. Furthermore, different strain rates are applied to analyse rate dependent behaviour. The storage time of the sand is also varied, since it influences the material characteristic of the binder in the cold box. An effective heating procedure is developed to characterise the mechanical material behaviour due to different isothermal loadings. The pressure dependence of multiaxial stress states is investigated in a pressure cell. The experimental data are intended to develop and identify a material model for sand, taking into account the strength–differential effect (S–D effect), rate and temperature dependence and the effect of hydrostatic stress states.     

电流变技术在车辆减振装置中的应用研究

电流变技术应用于车辆减振控制具有响应速度快、阻尼无级可调、能耗低等特点，可以通过适当的控制规律实现对结构振动的最优控制。本文通过对充气式电流变减振器原理进行分析，讨论了减振器阻尼力计算公式，它包括电流变液基础粘度引起的本底阻尼力、由电场作用引起的电致阻尼力和气室气体引起的压力三部分。开发了一种结构简单的充气式电流变液体减振器，对影响减振器性能的主要结构参数进行了分析讨论，给出了减振器设计中参数选择的一般原则和应注意的问题。通过台架实验，对所设计的电流变液体减振器性能进行了考察，得到了较好的示功图和速度特性曲线，为车辆路试奠定了基础。     

On the Strain Rate Sensitivity of Abs and Abs Plus Fused Deposition Modeling Parts

In this work the effect of strain rate on the tensile strength of fused deposition modeling parts built with Acrylonitrile-butadiene-styrene (ABS) and ABS plus material is presented. ASTM D638-02a specimens were built with ABS and ABS plus and they were tested on a Schenck Trebel Co. tensile test machine at three different test speeds, equal, lower, and higher to the test speed required by the ASTM D638-02a standard. The experimental tensile strength results were compared and evaluated. The fracture surfaces of selected specimens were examined with a scanning electron microscope, to determine failure mode of the filament strands. It was found that, as the test speed increases, specimens develop higher tensile strength and have higher elastic modulus. Specimens tested in the highest speed of the experiment had on average about 10% higher elastic modulus and developed on average about 11% higher tensile strength.     

Fatigue behaviour of low temperature carburised AISI 316L austenitic stainless steel

Low temperature carburising (LTC) was applied to AISI316L austenitic stainless steel and its effect on microstructure and fatigue behaviour was investigated. LTC treatment enhances surface hardness and wear resistance of the steel without reducing its corrosion resistance. Surface hardness up to 1150 Vickers was achieved in the carburised layer, thanks to the formation of the so-called “S-phase”, a carbon-supersaturated austenite phase. The XRD evaluation of treated material verified expanded austenite with no evidence of carbide precipitation. Rotating bending fatigue tests showed that the low temperature carburising treatment enhances the fatigue strength of the 316L steel by 40% with respect to the untreated material due to the high residual stresses present in the treated layer. A major temperature increase was found testing the LTC specimens, with a peak value at the end of the test up to 600 °C. By air cooling the LTC specimens during the tests, a further increase of fatigue strength up to 70% was achieved with respect to the untreated material. Fatigue cracks in the surface-treated specimens always nucleated near the boundary between the carburised case and the core.     

Tensile strength assessment of corroded small scale specimens

Tensile strength tests are performed on small scale corroded specimens, so as to derive their mechanical properties. The specimens were cut from a box girder that was initially corroded in real sea water conditions. As a result of the tensile tests the mechanical properties of the specimens are determined, namely modulus of elasticity, yield stress, tensile strength, resilience, fracture toughness and total uniform elongation. Regression equations are derived for the properties as a function of the degree of corrosion degradation. It is identified that those material parameters are influenced by the severity of corrosion degradation.     

高温材料的阻尼特性实验研究

采用双悬臂梁试件,通过基础激励下的共振驻留法,开发了一套高温材料在真空环境下的阻尼测试系统。研究了提高测试精度的方法,并分析了空气阻尼对阻尼测试结果的影响,并以Ti-6-4合金为对象,研究了阻尼随温度、应变幅值及振动频率的变化规律     

Tensile properties of 6061-T6 friction stir welds and constitutive modelling in transverse and longitudinal orientations

Tensile stress–strain properties of Al alloy 6061-T6 (AA6061-T6) and its butt welds produced by the friction stir welding (FSW) process were characterized in two different loading orientations. AA6061-T6 FS welds were made under three sets of welding conditions. Micro-hardness tests were performed to investigate microstructural evolution during the FSW process. Flat tensile specimens were machined normal and parallel to the weld line. Transvers and longitudinal tensile tests were run on the base material (AA6061-T6) and its FS welds in an Instron testing machine. The strength and ductility (or fracture strain) of the FS welds observed in the transverse orientation were substantially less than those in the longitudinal orientation. Constitutive modelling of uniaxial tensile stress–strain behaviour in both orientations was presented using a rate-independent Ludwik equation. In addition, microstructures of the base material and its FS welds were examined with optical and transmission electron microscopy to discuss the decrease in the flow stress level and the increase in the strain hardening rate of the FS welds.     

Fracture behaviour of diffusion bonded titanium alloys with strength mismatch

Abstract

The present study considers the effect of strength mismatch on the fracture behaviour of diffusion bonded joints between commercially pure (CP) Ti and Ti-6Al-4V (Ti64), including dissimilar joints and sandwich structures with strength undermatching and overmatching. The aim of the investigation is to determine the influence of the interlayer thickness (for both higher and lower strength interlayers) and the bond quality on the deformation behaviour and fracture toughness of the joints. The influence of mechanical heterogeneity (strength mismatch) on the fracture behaviour of the interface in dissimilar joints was also investigated. Round bars of CP Ti and Ti64 having a diameter of 40 mm were diffusion bonded as dissimilar butt joints and sandwich structures containing lower strength (undermatching) and higher strength (overmatching) interlayers of different thicknesses. Round transverse tensile specimens and standard four point bend (single edge notch bend) specimens were extracted from the joints via spark erosion cutting. The four point bend specimens were fatigue precracked to introduce a sharp crack after introducing machine notches at the centre of the interlayers in the sandwich structures and at the interface in the dissimilar joints, and tested at room temperature. Some specimens were also prepared with the crack positioned away from the interface to determine the effect of notch position on fracture behaviour. The effect of strength mismatch on the crack tip opening displacement fracture toughness parameter of the joints has been evaluated. Crack initiation, crack growth, and crack deviation processes have been examined and fracture resistance curves (R curves) constructed for the joints. These results were used to explain the influence of mechanical heterogeneity of the joints and interlayer thickness on fracture behaviour.     

混杂纤维人造花岗岩超精密摆线轮成形磨床床身的动静态特性研究

利用正交试验法,设计并制作了不同配合比的混杂纤维人造花岗岩试件,并对试件进行了抗压强度测试。利用SolidWorks建立了超精密摆线轮成形磨床三维模型,在ANSYS Workbench平台对相似结构的混杂纤维人造花岗岩、未添加纤维人造花岗岩以及铸铁(HT250)摆线轮成形磨床床身分别进行有限元分析。结果表明:(1)添加混杂纤维可以提高人造花岗岩材料强度;(2)混杂纤维人造花岗岩床身的等效变形最小,等效应力低,床身前5阶固有频率最高。     

Vergleichende Untersuchungen über die Aufstickung von niedrig- und hochlegierten Stählen sowie der Legierung NiMo 16 CrW in Ammoniak bei 300 bis 500°C

Comparative investigations into the nitruration between low and high alloy steels and the alloy NiMo 16 CrW in ammonia at 300 to 5OO°C The nitriding behaviour of high temperature high strength steels 13 CrMo 44, 10 CrMo 910 and 17 CrMoV 10, of the high alloy high temperature strength steels X 8 CrNiNb 16 13, the stainless steel Y 8 Cr 17 and nickel base alloy NiMo 16 CrW has been studied in ammonia at 300, 400 and 5OO°C, test durations being up to 1000 hours. The evaluation was based on determination of the nitriding depth preferentially with the aid of microhardness measurements. The structure of nitride layers and the structure changes due to nitrogen adsorption in the material are explained in connection with the time dependence of nitriding. The behaviour of specimens Passivated in air is shown as well as the influence of the surface pretreatment by depassivation or preoxidation and the influence of minor oxidising constituents (air, steam) in ammonia.     

脉冲TIG焊混合电弧模型

基于实际的电弧物理过程分析,设计了相应的电弧阻滞系数方程,结合经典的Mayr和Cassie模型,提出了脉冲钨极氩弧焊 (TIG) 的混合电弧模型;论述了电弧阻滞系数方程中阻滞参数的选取原则,给出了模型中其它相关参数的数值确定方法,并结合电弧的实际进行了参数设定;基于该混合模型,进行了电弧的静特性验证,以及不同频率下的动特性验证. 结果表明,该混合模型能够有效的模拟TIG脉冲电弧.     

Microstructure and mechanical properties of Alborex+SiCp/AS52 hybrid metal matrix composites

Abstract

AS52 based hybrid composites reinforced with aluminium borate whiskers and SiC particulates were fabricated by a squeeze casting method. In a hybrid preform, the volume fraction of the aluminium borate whisker was 15% and that of the SiC particulate was 5%. Microstructures of the specimens were observed using OM and SEM. In the hybrid composites, the Alborex whiskers were uniformly distributed in the matrix and a few agglomerations or clusters of SiC particulates were observed. Hardness and three point bending tests were carried out to measure the mechanical properties of the specimens. The mechanical properties of the hybrid composites were higher than those of whisker reinforced composites and the hybrid composite with finer size particulates showed higher strength than the one with coarse particulates.     

Application of a novel type Barkhausen noise sensor to continuous fatigue monitoring

A novel Barkhausen noise (BN) sensor with no need for external magnetization was tested and applied to continuous fatigue monitoring of mild steel and high strength steel specimens. This new type of sensor indicated an increase in the BN rms value under maximum tensile stress during one cycle in cyclic bending tests with increasing stress amplitude. The BN rms value under maximum compressive stress stayed, however, approximately constant. The reason for this behaviour was the stress-induced anisotropy of the BN. Bending fatigue experiments with constant stress amplitude and R=−1 were conducted at different stress levels. In addition to the BN also the acoustic emission of the specimen was measured. In the mild steel specimens the BN amplitude stayed constant after the initial saturation period, but just prior to the failure of the specimen the amplitude increased meaningfully. This increase occurred at the same time as the increase in the acoustic emission signal indicating the beginning of crack initiation and growth. In the high strength steel specimens the BN amplitude decreased after the initial saturation period. The increase of the BN signal started well before the failure of the specimen and even before the increase in the acoustic emission signal.     

Impact specimen geometry on T23 and TP347HFG steels behaviour during steam oxidation at harsh conditions

Ferritic T23 steel and austenitic TP347HFG steel have been studied with an emphasis on understanding the impact of specimen geometry on their steam oxidation behaviour. The selected materials were tested over a wide range of temperatures from 600 to 750°C. The tests were carried out in 100% steam conditions for 1000 hours. The tests indicated that the ‘curved-shaped’ specimens show slower mass gain, scale ticking and void nucleation rates than ‘bridge-shaped’ specimens (with flat and convex surfaces combined). Furthermore, a bridge TP347HFG sample showed the formation of lower amount of flaky oxide at 750°C.