Fatigue Residual Strength Research Articles

Residual fatigue strength of 48MnV crankshaft based on safety factor

Residual fatigue strength of 48MnV crankshaft was studied and analyzed based on safety factor. Three different status crankshafts were used to the hop-up tests, which maintain new after 500 h hop-up tests and after 1 000 h hop-up tests. Then, crankshafts were cut into unit cranks. The unit cranks were used to do endurance bending tests to get the residual fatigue strength. Finally, the results were analyzed based on safety factor. The results show that safety factor of crankshaft descends a little with the increase of the running time, and the residual safety factor is still much bigger than the endurable safety factor. Furthermore, after the crankshaft accomplishes a full life cycle, the residual fatigue strength of the crankshaft is enough to remanufacture and fulfill the next life cycle.

Integrity of hybrid steel-to-composite joints for marine application

There are many instances where the use of weight-saving polymer composite material for an entire structure is either too complex, too expensive or unfeasible. In these circumstances the use of a hybrid structure can incorporate the benefits of traditional (e.g. steel) construction coupled with the advantages of composite materials [e.g. glass-reinforced polymers, glass-reinforced plastic (GRP)] in weight-critical areas. A number of studies have been carried out on the static strength of hybrid steel-to-composite joints. In the present study, an experimental investigation was undertaken into the fatigue life characterization of a hybrid steel-to-GRP joint. It was found that the fatigue data correlated well with the statistical-based Weibull cumulative distribution function. In addition, post fatigue (in-plane and out-of-plane) residual strength tests were undertaken to ascertain the joint structural performance after cyclic loading. Finite-element-based progressive damage analyses incorporating damage initiation and propagation characteristics, showed good correlation with experimental results.

Fatigue Life and Residual Strength Analysis of Steel-Composite Joints

There are many instances where the use of weight saving composite materials for an entire structure is either; too complex, too expensive or unfeasible. In these circumstances the use of a hybrid structure can incorporate the benefits of traditional construction materials, for example steel, coupled with the advantages of composite materials in weight critical areas. In the present study, an investigation was undertaken into the fatigue life characterisation of a hybrid joint for marine application. In addition the residual strength of the joint, after a fixed number of fatigue cycles, was assessed under axial compression and bending loads. A progressive damage model was developed to predict the location of major stress concentrations, the path of damage and subsequent loss in stiffness of the joint under axial compression.

On static and fatigue strength determination of carbon fibre/epoxy composites Part 1: Experiments

This work seeks to investigate the static and fatigue properties and the failure mechanisms of T300/QY8911 carbon-fibre-reinforced composite laminates with different layups to optimize the stacking sequence effect. Three different layups have been studied, namely, [45/02/-45/902/-45/0/45/90]s, [45/-45/0/-45/0/45/90/45/0/-45]s and [45/0/-45/0/-45/0/45/0/90/0]s. The results for static strength and fatigue residual strength under different fatigue stress amplitudes are evaluated and compared with each other. The damage and failure mechanisms of the composite laminates are discussed. It is observed that all tension-tension fatigue damage patterns of the notched laminates are similar while the tension-tension fatigue properties vary with the laminate layup. The reduction of stress concentration caused by the tension-tension fatigue damage leads to an improvement of the residual strength of the notched specimens in contrast to their static strength properties. The damage mechanics of the notched laminates under compression-compression loading are more complex than those of the tension-tension fatigue specimens; their damage patterns are influenced by the test clamping fixture, the layup, the size of specimens and the diameter of the hole. The residual strengths are lower than those of the specimens without fatigue damage. It is verified that in a high-temperature and moisture environment, there is a decrease in static compression strength. The results of this study provide an insight into fatigue damage development in composites and constitute a fundamental basis for the development of a strain-based residual strength model.

Two New Practical Models for Estimating Reliability-Based Fatigue Strength of Composites

This paper outlines two new practical models to evaluate fatigue residual strength and the overall range of life for reliability-based design. A new fatigue-driven residual strength surface model with four parameters is derived based on an expression form of power function product to estimate the parameters more easily and expediently, and logically characterize the physical characteristics and the phenomenological quantitative laws. A more appropriate S-N curve formulation with four parameters is presented to cover overall life range. By means of the likelihood principle and the linear regression, the parameter determination formulae of these two models are respectively established to deal with the test data effectively and easily. The probability distributions for these two models are also given. Finally, the models are applied to two sets of experimental data, demonstrating the practical and effective use of the proposed models. It is shown from these examples that fatigue-driven residual strength and the overall range of life can be obtained realistically according to the small sample test data using the new formulae.

On static and fatigue strength determination of carbon fibre/epoxy composites Part 2: Theoretical formulation

This paper outlines a practical model to evaluate fatigue residual strength for reliability-based design. A new formulation is presented for a fatigue-driven residual strength surface based on controlling fatigue strain. The parameter determination formulae of the residual strength surface are established to deal with the test data effectively and easily. Finally, the model is applied to experimental data, demonstrating the practical and effective use of the proposed model. It is shown that fatigue-driven residual strength can be obtained realistically according to the small sample test data using the new formulae.

浸炭焼入れ薄肉対称ウェブ構造平歯車の残留応力と曲げ疲労強度に及ぼす浸炭部の影響(O.S.02-1 歯車の強度(1))

This paper presents a study on effects of case-carburized parts on residual stress and bending fatigue strength of case-carburized thin-rimmed spur gears with symmetric web arrangement. A heat conduction analysis and an elastic-plastic stress analysis during the case-carburizing process were carried out for various case-carburizing conditions by the three dimensional finite-element method (3D-FEM), considering changes of the thermal expansion coefficient and the yield stress with the temperature, and then residual stresses were obtained. Bending fatigue tests were carried out for different case-carburized thin-rimmed spur gears with symmetric web arrangement. Effects of case-carburized parts on the residual stress and the bending fatigue strength were examined. These results were also compared with those of solid gears.

Characterization of fretting fatigue crack initiation processes in CR Ti–6Al–4V

A study was conducted to quantify fretting fatigue damage and to evaluate the residual fatigue strength of specimens subjected to a range of fretting fatigue test conditions. Flat Ti–6Al–4V specimens were tested against flat Ti–6Al–4V fretting pads with blending radii at the edges of contact. Fretting fatigue damage for two combinations of static average clamping stress and applied axial stress was investigated for two percentages of total life. Accumulated damage was characterized using full field surface roughness evaluation and scanning electron microscopy (SEM). The effect of fretting fatigue on uniaxial fatigue strength was quantified by interrupting fretting fatigue tests, and conducting uniaxial residual fatigue strength tests at R=0.5 at 300 Hz. Results from the residual fatigue strength tests were correlated with characterization results. While surface roughness measurements, evaluated in terms of asperity height and asperity spacing, reflected changes in the specimen surfaces as a result of fretting fatigue cycling, those changes did not correspond to decreases in residual fatigue strength. Neither means of evaluating surface roughness was able to identify cracks observed during SEM characterization. Residual fatigue strength decreased only in the presence of fretting fatigue cracks with surface lengths of 150 μm or greater, regardless of contact condition or number of applied fretting fatigue cycles. No cracks were observed on specimens tested at the lower stress condition. Threshold stress intensity factors were calculated for cracks identified during SEM characterization. The resulting values were consistent with the threshold identified for naturally initiated cracks that were stress relieved to remove load history effects.

2308 高周波焼入れ焼結金属歯車の残留応力・硬化層と曲げ疲労強度

A 3D-FEM simulation program for induction hardening of sintered metal gears was made up. An electromagnetic field analysis, a heat conduction analysis and an elastic-plastic stress analysis during the induction hardening process of sintered metal gears were carried out by using this program, considering changes of the magnetic permeability, the resistivity, the thermal expansion coefficient and the yield stress with the temperature. The measurement of hardness distribution and the bending fatigue test of induction hardened sintered metal gears were performed. Effects of the heating time on residual stress, hardened layer and bending fatigue strength of induction hardened sintered metal gears were examined, and compared with those of induction hardened wrought steel (S35C) gears.

Thermal cycling aging effects on microstructural and mechanical properties of a single PBGA solder joint specimen

This paper reports on an experimental study on how thermal cycling aging exposure changes the solder joint microstructure, intermetallic layer thickness and the residual shear strength and fatigue life in a single plastic ball grid array (PBGA) solder joint specimen. The single BGA solder joint specimen was specially designed to evaluate the microstructure and mechanical properties of three different batches of solder joint after subjected to 0, 500, 1000, and 2000 cycles of thermal cycling aging (-40/spl deg/C to 125/spl deg/C). It is important to relate the effects of thermal cycling aging on the changes of the microstructural and intermetallic layer thickness to the residual shear strength and fatigue life of solder joints subjected to thermal cycling aging exposure. The results of this study shows that the microstructural and intermetallic development due to thermal cycling aging has a major impact on the residual mechanical and fatigue strength of the solder joint. It was noted that the solder joint shear strength and residual fatigue life degrades with exposure to thermal cycling aging.

211 浸炭焼入れ歯車の残留応力と曲げ疲労強度に及ぼす側面浸炭焼入れの影響(OS1-3 伝動装置の基礎と応用)

This paper presents a study on effect of gear-side case-hardening on residual stress and bending fatigue strength of case-hardened spur gears. The bending fatigue tests of case-hardened gears with different case depths and case-hardened parts (tooth surface and gear-side) were carried out, and the test results were examined on the basis of the residual stresses calculated by the three dimensional finite-element method (3D-FEM). Effects of the case depth, the residual stress and the gear-side case-hardening were determined to the considerable extent.

An experimental study of the influence of fibre–matrix interface on fatigue tensile strength of notched composite laminates

Abstract The objective of this study was to investigate the effect of fibre–matrix interfacial adhesion on fatigue residual strength of polymer matrix composite laminates containing a circular hole. Composite laminates were manufactured using surface-treated and -untreated carbon fibres, and the interfacial adhesion was quantified by measuring the transverse flexural strength of the two material systems. Tensile–tensile cyclic fatigue experiments were conducted at three load levels. Residual strength of notched laminates, subjected to cyclic loading was then measured for the two composite systems. Damage mechanisms were analysed using C-scan and SEM fractography and correlated with notched residual strength.

Fatigue Damage Mechanisms of Bridging Fibers in Titanium Metal Matrix Composites1

This paper investigates the fatigue damage mechanisms of SiC fibers bridging a fatigue crack in unidirectional reinforced titanium matrix composites. For this purpose, an experimental/computational fiber fracture model is developed on the basis of the occurrence of two damage events taking place along a bridging fiber. These events are the time-dependent evolution of axial stresses and the simultaneous strength degradation of the fiber due to cyclic-related damage processes. The stress evolution in a fiber is calculated using the finite element method employing a cylinder model of a fiber embedded in a cracked matrix phase. The model considers the visco-plastic behavior of the matrix phase at elevated temperature loadings. The failure strength of the as-received SiC fiber are determined through a series of monotonic tension, residual fatigue strength and fatigue-life tests performed on SiC fibers at different temperatures. In order to take into account the notch-like effects resulting from the presence of fiber coating cracks and possible deflection of fiber/matrix interfacial cracks, the fatigue strength of the as-received SiC fiber was modified using elastic stress localization. The resulting fatigue strength of bridging fibers was found to be about 56 percent less than the corresponding strength of as-received fibers. The fiber stress evolution curve and the modified fatigue strength curve were then combined to predict the life of bridging fibers. Results of the model are compared with those obtained experimentally for bridging fibers in SiC/Timetal-21S composite subjected to load conditions including low and high loading frequency at 500 and 650°C. [S0094-4289(00)01804-1]

1725 SMC の引張疲労後の残留強度に及ぼすサイジング剤の影響

SMCs of different sizing are prepared and static tensile strength of fatigued materials, that is, residual strength was investigated and it is tried to make relationship among strength, fatigue mechanisms and sizing clear. The fatigue residual strength of SMC were measured after tensile cyclic loading. The residual strength of fatigue-damaged SMC treated with Soft sizing didn't degraded in spite of increasing of fatigue cycle. But the residual strength of fatigue-damaged SMC treated with Hard sizing-degraded. Researching on the fracture surface of virgin and fatigue-damaged materials, it is pointed out that the micro debonding mechanism around and in the glass fiber strands is changed by number of cyclic loading.

Impact damage and hygrothermal effects on fatigue bending strength of orthotropy composite laminates

This paper focuses on fracture mechanisms experimentally based on the scanning acoustic microscope (SAM) when subjected to impact damages, i. e., foreign object damages (FOD), and also on the influence of impact damages and hygrothermals on residual fatigue bending strength of CFRP laminates. Composite laminates used in the experiments are CF/Epoxy orthotropy laminated plates, [04/904]s. A steel ball launched by an air gun impacts on CFRP laminates to generate impact damages. Bending fatigue tests are periodically interrupted for a nondestructive evaluation (NDE) measurement of the progressive damages to build the fracture mechanism based on impact damages, and three-point fatigue bending tests are carried out to investigate the influence of hygrothermals on the effect of the residual bending fatigue strength of CFRP laminates.

Residual Stress Reduction and Fatigue Strength Improvement by Controlling Welding Pass Sequences

The effects of residual stress on fatigue strength at a weld toe in a multi-pass fillet weld joint were evaluated. The residual stresses in the weld joints were varied by controlling the sequence of welding passes. The residual stress at the weld toe was 80 MPa in the specimen whose last welding pass was on the main plate side, but it was 170 MPa in the specimen whose last pass was on the attachment side. The fatigue strength was nearly the same at high stress amplitude for both specimens, but the fatigue strength of the specimen whose last weld pass on the main plate was higher than that of the other specimen at low stress amplitude. This difference is due to the magnitude of the initial residual stress and the relaxation of the residual stress under fatigue cycling. The effects of the residual stress were shown in a modified Goodman diagram, in which residual stress is treated as a mean stress. [S0094-4289(00)01701-1]

Relationship Between Pore Structure and Mechanical Properties of Ordinary Concrete Under Bending Fatigue

Progressive macro damage of concrete under fatigue loading is caused by the change of its internal micro-meso properties such as pore structure. In this study, porosity, pore size distribution, and specific surface area of ordinary concrete at different fatigue stages were investigated using mercury intrusion, helium flow, and nitrogen adsorption (BET) methods. These properties changed with increasing loading cycles and could be taken as micro-meso damage parameters to evaluate macro fatigue damage of concrete. Test results showed that both porosity in mortar (mainly macro pores) and interface between mortar and coarse aggregates (interfacial cracks) developed at a similar rate. The corresponding residual bending fatigue strength and dynamic bending Young’s modulus were also obtained and their relationships with these micro-meso properties were established. The “intrinsic bending strength” and “intrinsic bending Young’s modulus” were predicted from these relationships.

Residual fatigue strength and stiffness of ordinary concrete under bending

On the basis of the fatigue equation that had been previously proposed by the authors, a new formula for predicting the residual fatigue strength of ordinary concrete was deduced. This formula was further verified and modified by the flexural tests on the concrete beam specimens and compared with other previous test data. Also, some residual fatigue stiffness properties of concrete such as Young's modulus, Poisson's ratio and shear modulus were investigated using non-destructive testing techniques. There was a good correlation between the stiffness properties and the residual fatigue strength.

Estimation Method of Residual Stress Distribution and Fatigue Life Takaing the Effect of Welding Procedure Sequence into Consideration in Welded Build-up Structures

It is known that fatigue strength is affected by stress concentration depended on local shape of weld toe and welding residual stress. Fatigue strength of welded build-up structures decreases considerably because there are large tensile residual stresses and stress concentration at the fatigue crack initiation part in these structures.Authors showed that fatigue strength of the corner boxing joints and continuous fillet weld joints with load carrying girder increases very much by turning the tensile residual stress to compressive ones. Flame line heating on appropriate part enables to change the residual stress distribution. These results show that residual stress has a considerable influence on fatigue strength of welded build-up structures.Residual stress at the fatigue crack initiation part depends on welding procedure sequence near this part. Because the change of welding sequence means the change of thermal cycle given into this part by welding.The purpose of this paper makes clear the effect of welding procedure sequence on residual stress distribution and fatigue strength. Two different welding sequence specimens which have continuous fillet weld joints with load carrying girder were used. One of fatigue crack initiation part is the toe of final welding. The other is different part from final welding.Residual stress and fatigue life was investigated by using these specimens. Moreover, the estimation of residual stress distribution taking the welding sequence into consideration was carried out by using elastic finite element analysis based on inherent stress method.As a result of these investigations and analyses, it is clear that welding sequence has a considerable influence on residual stress distribution and that fatigue strength can be enhanced considerably by changing of welding sequence.

Damage Behavior and Residual Bending Fatigue Strength of CFRP Composite Laminates Subjected to Impact Loading

Damage Behavior and Residual Bending Fatigue Strength of CFRP Composite Laminates Subjected to Impact Loading