Fatigue assessment of arc welded automotive components using local stress approaches: Application to a track control arm

The applicability of the structural and notch stress approach is examined on the basis of arc welded and dynamically loaded steel structures, taken from the automotive sector. In detail, this is a transverse control arm. Components and specimens with critical regions of failure are tested under cyclic loading with constant and variable amplitudes. With the help of strain gauges, the crack initiation is determined. The specimens are the basis for the application and evaluation of the different approaches for the assessment of fatigue life. The numerical determination of the nominal, structural and notch stresses is performed with finite-element models. Finally the experimental and computational results allow the derivation of structural and notch Woehler S-N curves.     

Composite heddle frame for high-speed looms

A heddle (or heald) frame is the major part of a loom that produces woven cloth by insertion of weft yarns between warp yarns. Warp yarns are manipulated by many heddles fixed in a heddle frame. Recently, the up and down speed of heddle frames has been increased much for the increase of productivity, which induces higher inertial stresses and vibrations in the heddle frame. Conventional aluminum heddle frames have limits for the speed increase due to their low fatigue flexural strength as well as low bending stiffness. The estimated fatigue life of the aluminum heddle frame was 6 months at 600 rpm and infinite at 400 rpm, which was the same results reported by textile industries. Since carbon fiber epoxy composite materials have high specific fatigue strength (S/ρ), high specific modulus (E/ρ) and high damping capacity, in this paper a composite heddle frame was designed and manufactured. The optimum box type cross-sectional shape of the heddle frame and stacking sequence were determined by finite element analysis. The box type composite structure with several ribs was manufactured with prepregs by the autoclave vacuum bag process. Then the static and dynamic characteristics of the composite heddle frame and the aluminum heddle frame were measured and compared.     

Fatigue strength analysis of a welded railway vehicle structure by different methods

The endurance limit approach with maximum amplitude loading (constant loading amplitude) and the cumulative damage approach with variable amplitude loading are both established methods for the fatigue assessment of the bogie frame of a rolling stock. These methods are presented for the vertical main loading of a bogie frame for a light rail vehicle. Assessments are carried out for the normative load requirements according to the relevant standard EN 13749 [1] and also for a vertical force range spectrum deriving from a multiple body system simulation of this railway vehicle. The multiple body system simulation supplies more realistic loads depending on the actual railway application conditions. These different fatigue assessments allow a comparison of the normative load requirements with realistic load assumptions.In general the stress analysis is based on the nominal stress approach. Additionally, for the area subject to the maximum stress, a notch stress analysis is carried out. The comparison of stress analyses for some selected stress points shows the potential and the advantages of the fatigue assessment with the real loading assumptions and with different evaluation methods.     

Fatigue and Corrosion Fatigue of High-Nitrogen Austenitic Stainless Steel

High nitrogen contents in solid solution as well as appropriate strengthening mechanisms in austenitic stainless steels can result in very high corrosion resistance. This is true in both air environment and in simulated human body fluids (corrosion fatigue). High cycle corrosion fatigue data are listed and compared with similar data for titanium base and cobalt base implant materials. Thus high nitrogen austenitic stainless steels are candidates to replace other stainless steels as implant materials.     

Fatigue strength analysis of welded joints in closed steel sections in rail vehicles

A great need exists for practicability and reliability analyses of the various dimensioning concepts in railway vehicle production, as currently parts are commonly sized according to the nominal stress concept. Although Finite Element Analysis is used for the dimensioning of parts according to the nominal stress concept, no use is made of the locally resolved information from these calculation methods. Concepts based on local stress are highly applicable, as the Finite Element Analysis allows detailed modelling of critical areas of parts.     

Evaluation of nominal and local stress based approaches for the fatigue assessment of seam welds

In the context of the German joint research project “Applicability of fatigue analysis methods for seam welded components”, fatigue tests were performed by five universities and institutes on welded components, welded parts of larger structures as well as component-like samples of weld details. The sheet thickness t was in the range 1 mm ? t ? 20 mm. The welding parameters for all test coupons and structures tested were chosen according to the industrial production process. Based on the data acquired, nominal, structural and notch stress approaches were analysed with regard to applicability and quality of assessment. The actual weld geometry except the real notch radii was taken into account within the notch stress approach. For the notch radii various values, the reference radii 0.05, 0.3 and 1 mm, were applied.Experimental and numerical results for welded steel components are presented.Approximately equivalent scatter ranges were obtained when applying the various approaches based on the current state of the art. It should be noted that both the nominal and the structural stress approaches are limited in their application compared to the notch stress approach. A comparison of the scatter bands obtained for the various approaches is subject to limitations because it was necessary, in each case, to use different test series as the basis for determining the scatter bands.     

铜基引线框架材料的研究与发展

引线框架材料是半导体元器件和集成电路封装的主要材料之一,其主要功能为电路连接、散热、机械支撑等。随着IC向高密度、小型化、大功率、低成本方向发展,集成电路I/O数目增多、引脚间距减小,对引线框架材料提出了高强度、高导电、高导热等多方面性能上的要求。由于拥有良好的导电导热性能,铜合金已成为主要的引线框架材料。本文对电子封装铜合金引线框架材料的性能要求、国内外研究与发展等进行了综述。     

Fatigue crack growth in railway axles: Assessment concept and validation tests

Railway axles are safety relevant components which are usually designed for up to 30 years of service. Besides the experience based definition of inspection intervals, the application of fracture mechanics tools is currently being introduced as an appropriate method. Basic fatigue crack growth data both in the range of stable crack propagation and near the threshold have been experimentally determined for the heat-treated railway axle steels 25CrMo4 (EA4T) and 34CrNiMo6+QT under constant and variable amplitude loading at relevant stress ratios (predominantly fully reversed load cycles, R = −1). For the computational modelling of fatigue crack propagation, a generally applicable stress intensity factor solution has been derived by finite-element analyses. The results are employed for predicting fatigue crack growth in a reference railway axle within the shaft and in the fillet zone near a press fit. Additionally, the influence of press fitting on the crack propagation behaviour in a fillet is discussed. Finally, fatigue crack growth curves experimentally determined on 1:3 and 1:1 scaled axles at constant and variable amplitude loading are compared to the test results for standard M(T) specimens, as well as to respective analytical predictions.     

Fatigue characterization and modeling of 30CrNiMo8HH under multiaxial loading

Fatigue of 30CrNiMo8HH steel alloy has been studied thoroughly. Uniaxial cyclic tension-compression, cyclic torsion, proportional tension-torsion, and non-proportional tension-torsion at various strain ratios have been considered. Tests were performed at standard laboratory conditions on solid and tubular specimens machined from an actual driveline component. Fractography was conducted on the tested samples to investigate the fatigue mechanisms involved. Under torsion, large numbers of early micro cracks were found to emanate from the sample's surface, with a few propagating into very long longitudinal cracks. In biaxial tests, cracks tend to propagate into the gauge reducing the cross section area. A strain energy density fatigue parameter has been employed for life prediction of the material under uniaxial and biaxial loading. The life prediction method is based on two different cracking mechanisms that agree with the observed cracking mechanisms in torsion and biaxial loading of 30CrNiMo8HH steel alloy studied here. Energy-based properties are obtained and the predicted lives are compared to experimental results. The results obtained agree well with experiments.     

Fatigue behavior of tailor (laser)-welded blanks for automotive applications

The drive towards weight reduction in the automotive industry has led to the use of tailor-welded blanks (TWBs) for structural applications. This work is aimed at evaluating the fatigue behavior of the TWBs having different thickness combinations and compositions with and without zinc coating. The results showed that TWBs made from zinc-coated/galvanized steels exhibited a lower fatigue limit as compared with the TWB combination from uncoated bare metals. This was attributed to the intergranular cracking in the galvanized TWBs caused by the presence of zinc penetrating beneath the sheet surface. The fracture surface of the uncoated TWB was basically characterized by the fatigue striations.     

An experimental investigation of the static and fatigue fracture behaviour of hybrid composite/metal joints for a tilting car body

The hybrid composite joint structures considered in this work, for application in a tilting railroad car body, are subjected to shear and bending loads. Two types of the joint specimens were fabricated and tested under both static and fatigue conditions: a hybrid bolted-joint specimen subjected to a shear loads, and a hybrid beam-joint specimen for the bending tests. The fracture behaviours of these specimens under static loads were different from those under cyclic loads. For the hybrid bolted-joint specimens, static shear loads caused a pure shear fracture in the bolt pin body itself. However, cyclic fatigue shear loads brought about an opening-mode fracture at the local site of the bolt which was the valley of the screwed region of the bolt pin and/or the perpendicularly angled region between the bolt head and the pin body. On the other hand, for the hybrid beam-joint specimens, static bending loads caused shear deformation and fracture in the honeycomb core region, while fatigue cyclic bend loading caused delamination along the interface between the composite skin and the honeycomb core, and/or caused a fracture in the welded part jointed with the steel under-frame. These fracture behaviours could arise in other industrial hybrid joints with similar sub-structures, and were used in developing a design parameter to improve a hybrid joint structure.     

基于Kriging模型和无迹卡尔曼滤波的转向架构架模型修正

为提高转向架构架模型的修正效率和实时性,提出了一种基于Kriging模型和无迹卡尔曼滤波的模型修正方法.首先,对构架进行模态分析,引入信息熵确定模态阶数来优选频响函数频率区间.其次,构造Kriging模型,将频响函数经过小波变换并提取第4层低频系数作为Kriging模型输出,并通过改进的灰狼算法(grey wolf o...     

引线框架铜合金氧化特性的研究现状

铜合金由于具有优良的导电导热性能,已在现代集成电路塑料封装中占据了引线框架材料80%的份额。但铜合金容易氧化,其氧化膜被认为是塑料封装再流焊工艺中的分层和裂纹的主要原因之一,因此引线框架铜合金的氧化特性引起了人们的广泛注意。为获得铜合金引线框架良好的可靠性,不少材料工作者对铜合金在塑料封装中的氧化特性及其对铜合金与环氧树脂模压料（EMC）的粘接强度的影响进行了研究,为此,本文对引线框架合金的氧化物结构及动力学、铜合金与环氧树脂模塑料（EMC）粘接强度的影响因素等领域的研究进行了综述。     

Effect of Varying Carbon Content and Shot Peening upon Fatigue Performance of Prealloyed Sintered Steels

The aim of the work was to find out how the modification of surface treatment and microstructures affect the fatigue characteristics of the considered sintered materials.Two different systems were prepared:as-sintered and shot peened prealloyed sintered(Astaloy CrL based)steels with addition of 0.5%and 0.7%C.Sintering was carried out in laboratory tube furnace in an atmosphere of pure gases 75%N2+25%H2.The sintering temperature was 1180-C and sintering time was 60 min.Heating and cooling rates were 10-C/min...     

Fatigue damage assessment for a spectral model of non-Gaussian random loads

In this paper, a new model for random loads–the Laplace driven moving average–is presented. The model is second order, non-Gaussian, and strictly stationary. It shares with its Gaussian counterpart the ability to model any spectrum but has additional flexibility to model the skewness and kurtosis of the marginal distribution. Unlike most other non-Gaussian models proposed in the literature, such as the transformed Gaussian or Volterra series models, the new model is no longer derivable from Gaussian processes. In the paper, a summary of the properties of the new model is given and its upcrossing intensities are evaluated. Then it is used to estimate fatigue damage both from simulations and in terms of an upper bound that is of particular use for narrowband spectra.     

Analysis of Acoustic Emission energy release during static fatigue tests at intermediate temperatures on Ceramic Matrix Composites: Towards rupture time prediction

Ceramic Matrix Composites (CMCs) such as woven SiC_f/[Si–B–C] are used in aeronautical engines. Expected lifetimes in service conditions are tens of thousands of hours and therefore unattainable in laboratory tests. This paper shows the potential of Acoustic Emission (AE) based approach to lifetime prediction of CMCs. The energy of AE events is used as a measure of stress-induced damage during static fatigue at intermediate temperatures. The energy released by sources was determined from the signal energy received by two sensors, the effects of attenuation due to propagation distance were eliminated. A method for real-time analysis of energy release has been developed. It allows the identification of a characteristic time at 55% of the measured rupture time. This characteristic time reflects a local critical behavior described by the Benioff law and it indicates a second damage phase when subcritical crack growth in fibers is predominant.     

Tensile and Isothermal Fatigue Behaviors of Mg-12Gd-3Y-0.5Zr Alloy at High Temperature

Tensile and isothermal fatigue tests were carried out on an as-rolled Mg-12Gd-3Y-0.5Zr alloy and its heat-treated counterpart at different temperatures. The experimental results show that the ultimate tensile strengths of two alloys decrease very slowly with increasing temperature up to 200?C. The ultimate tensile strength of heat-treated Mg-12Gd-3Y-0.5Zr is slight lower than that of as-rolled counterpart; however, the fatigue strength of heat-treated alloy is higher. The mechanism of fatigue failure was in...     

Fatigue of bonded steel interfaces under cyclic shear loading and static normal stress

Hybrid joints that combine mechanical fastening and bonding provide potential joining alternatives for high strength steel structures. An experimental and analytical research program has been initiated to assess the static and cyclic Mode II shear strength of epoxy bonded steel interfaces subjected to static normal (Mode I) pre-stress. During cyclic loading, shear stress vs. interface displacement could be divided into elastic and inelastic regions with a power law equation describing the inelastic curve. Hysteresis loop shape varied with normal stress, shear stress and accumulated fatigue cycles. A shear stress amplitude threshold equal to about 50% of the fracture shear stress was observed.     

基于ANSYS的高压气瓶疲劳分析设计

随着工业气体的高速发展,高压气瓶使用次数日益增多,从而导致气瓶承受循环载荷的情况也随之增加,产生疲劳失效事故的可能性也在加大,人们开始越来越重视气瓶的疲劳分析设计。本文以某高压无缝钢瓶为实例,介绍了基于ANSYS软件的气瓶疲劳分析设计中主要步骤和注意事项。     

Fatigue performance of a self-piercing rivet joint between aluminum and glass fiber reinforced thermoplastic composite

Lightweight structures are more and more widely used in the automotive industry due to the growing importance of environment regulations related to CO₂ emissions. In this context of saving weight, composites offer an alternative to metals because they can achieve a better stiffness to weight ratio. A problematic becomes crucial: which process can be used to join efficiently composite and metallic parts?An innovative way would be the application of self-piercing riveting to thermoplastic composite–metal structure. Since the self-piercing riveting does not require a pre-drilled hole, the time process is short. Nevertheless, this process generates damage in the composite such as fiber cutting and delamination.The aim of this work is to evaluate the fatigue strength of a PA6.6-GF (Glass Fiber reinforced Polyamide 6.6)/Aluminum assembly joined by self-piercing riveting. Experimental results show that the SPR joint achieve high fatigue resistance on uniaxial shearing test. The joint strength at 2 · 10⁶ cycles is more than half of the joint strength in static. Joint manufacturing process parameters like the rivet shape were investigated. Some fatigue tests were performed under severe environmental conditions like high temperature. This study shows that process parameters have less influences on the joint strength than the parameters that impact the composite resistance such as the composite type and the test temperature. The composite stresses evolution is useful for the failure modes analyses.