Showing papers on "Fatigue limit published in 2000"

Progressive fatigue damage modeling of composite materials, Part I : Modeling

Abstract: In this research a modeling technique for simulating the fatigue behaviour of laminated composite materials, with or without stress concentrations, called progressive fatigue damage modeling, is es...

Properties of Aluminum Alloys: Tensile, Creep, and Fatigue Data at High and Low Temperatures

Abstract: Contents include: Typical Mechanical Properties of Wrought and Cast Aluminum Alloys at Various Temperatures - tensile properties at subzero temperature, at temperature after various holding times at the test temperature, and at room temperature after exposure at various temperatures for various holding times creep rupture strengths for various times at various temperatures stresses required to generate various amounts of creep in various lengths of time rotating-beam fatigue strengths modulus of elasticity as a function of temperature Fatigue Data - fatigue strength of wrought aluminum alloys (approximate average values as determined in tests of smooth and notched rotating-beam fatigue machines), axial stress fatigue strength of wrought aluminum alloys (at various stress ratios, smooth and notched specimens), average fatigue strength for aluminum and aluminum alloy flat sheet specimens (under complete reversed flexure), cantilever-beam fatigue test results of aluminum alloys at elevated temperatures following stabilization at the test temperature.

Progressive Fatigue Damage Modeling of Composite Materials, Part II: Material Characterization and Model Verification:

Abstract: To validate the fatigue progressive damage model, developed in the first part of this paper, an experimental program was conducted using graphite/epoxy AS4/3501-6 material. As the input for the model, the material properties (residual stiffness, residual strength and fatigue life) of unidirectional AS4/3501-6 graphite/epoxy material are fully characterized under tension and compression, for fiber and matrix directions, and under in-plane and out-of-plane shear in static and fatigue loading conditions. An extensive experimental program, by using standard experimental techniques, is performed for this purpose. Some of the existing standard testing methods are necessarily modified and improved. To evaluate the progressive fatigue damage model, fatigue behaviour of pin/bolt-loaded composite laminates is simulated as a complicated example. The model is validated by conducting an experimental program on pin/bolt-loaded composite laminates and by comparison with experimental results from other authors. Different...

The validation of some methods of notch fatigue analysis

Abstract: This paper is concerned with the testing and validation of certain methods of notch analysis which the authors have developed theoretically in earlier publications. These methods were developed for use with finite element (FE) analysis in order to predict the fatigue limits of components containing stress concentrations. In the present work we tested and compared these methods using data from standard notches taken from the literature, covering a range of notch geometries, loading types, R-ratios and materials: a total of 47 different data sets were analysed. The greatest predictive success was achieved with critical-distance methods known as the point, line and area methods: 94% of these predictions fell within 20% of the experimental fatigue limits. This was a significant improvement on previous methods of this kind, e.g. that of Klesnil and Lucas [(1980) Fatigue of Metallic Materials, Elsevier Science]. Methods based on the Smith and Miller [(1978) Int. J. Mech. Sci. 20, 201–206] concept of crack-like notches were successful in 42% of cases; they experienced difficulties dealing with very small notches, and could be improved by using an ElHaddad-type correction factor, giving 87% success. An approach known as ‘crack modelling’ allowed the Smith and Miller method to be used with non-standard stress concentrations, where notch geometry is ill defined; this modification, with the same short-crack correction, had 68% success. It was concluded that the critical-distance approach is more accurate and can be more easily used to analyse components of complex shape, however, the crack modelling approach is sometimes preferable because it can be used with less mesh refinement.

Laser shock peening for fatigue resistance

Abstract: Laser shock peening produces a compressive residual stress in the surface of metallic materials, which significantly increases fatigue life in applications where failure is caused by surface-initi ated cracks. Laser shock peening is applied by using a high energy pulsed laser to create a high amplitude stress wave or shock wave on the surface to be treated. This stress wave propagates into the material, causing the surface layer to yield and plastically deform, and thereby, develop a residual compressive stress. Where comparisons have been made to shot peening, the magnitude of the residual stresses at the surface are similar, but the compressive stresses from laser peening extend much deeper below the surface than those from shot peening. The resulting fatigue life enhancement is often greater for laser peering than it is for shot peening. In addition to fatigue strength improvement, laser peering can also locally strain harden thin sections of parts or strain harden a surface.

Effect of ion nitriding on fatigue behaviour of AISI 4140 steel

Abstract: Ion nitriding has become a popular thermo-chemical surface treatment, which is being used to develop fatigue and wear characteristics of steels. Besides the increased strength, the formation of high compressive residual stresses in the case region causes remarkable improvement in fatigue properties of steels. In this study, the effect of case depth on fatigue performance of AISI 4140 low alloy steel has been investigated by conducting a series of rotary bending fatigue tests at the frequency of 95 Hz, on hour glass shaped, 4 mm diameter specimens, which had been ion nitrided at 748 K for 1, 3, 8 and 16 h. Up to 50% improvement in fatigue strength of the steel has been attained by ion nitriding, depending on the case depth formed during the process. The comparison of test results between ion and liquid nitrided specimens having the same case and core properties, has shown that a 12% increase in fatigue strength could be reached by ion nitriding with respect to conventional, salt bath nitriding process. An attempt was made to establish some empirical relationships between the parameters defining relative case depth, which consider case depth and specimen size together, and fatigue strength of ion nitrided steel. It was obtained that the subsurface ‘fish eye’ type crack formation is the dominant fatigue crack initiation mechanism in ion nitrided AISI 4140 steel, and a map has been constructed to illustrate the locations of crack origins depending upon the case depth and the cyclic stress acting on specimens. It was also tried to explain the conditions promoting the ‘fish eye’ crack formation by analysing the combined effects of residual and applied stress patterns as well as inclusion size.

Titanium alloys for fracture fixation implants

Abstract: This paper is intended to provide an overview of the composition, mechanical properties, biocompatibility, and clinical applications for titanium alloys that are used for fracture fixation implants. A new class of titanium implant alloys has emerged in recent years that exhibits a β microstructure and a unique combination of mechanical properties. Important information regarding notch sensitivity testing and clinical significance is also discussed. Attributes such as stress corrosion cracking resistance, fatigue strength, and wear characteristics are also essential for specific clinical applications, but are beyond the scope of this presentation.

Experimental reconfirmation of characteristic S-N property for high carbon chromium bearing steel in wide life region in rotating bending

Abstract: In fatigue tests of high strength steels and surface hardened steels, a characteristic fatigue behavior such that S-N curve tends to come down again in the long life region of N>107 was often observed and reported by many researchers. When the mechanical design is based on the fatigue limit of the material, the above aspect introduces a typical difficulty to provide the reliability of the mechanical structures. In order to clarify such S-N characteristics in wide life region, a series of fatigue tests were performed by means of same type fatigue testing machines and same type of fatigue specimens in a definite high carbon chromium steel for the use of bearing as a collaborative study by the authors. Thus the complicated S-N property of this steel was tentatively interpreted as duplex S-N characteristics given by superposition of S-N curves for the respective fracture modes of the surface-originated fracture and the inclusion-originated fish-eye fracture.

Strength and fracture of aluminum alloys

Abstract: In aluminum alloys, it is general that dimple type fracture occurs from inclusions or second phases particles. Intergranular, local shear and delamination type fractures are also sometimes observed. On Al–Li alloy (A2091), effect of inclusion particles on fracture behavior is analyzed using HRR singularity and Eshelby type internal stress analysis. Fracture of inclusions of CuAl2 and Al2CuMg is observed (5–8 μm) and their strength is estimated about 710 MPa and decreased with increasing particle size. Fracture of Al3Zr or Al3Ti particles is not observed. Moreover, it is clarified that delamination occurs when the normal stress against the grain boundary attains 116 and 113 MPa at liquid He and room temperature, respectively. Moreover, newly developed high strength Al–Nb wire with 1 Gpa is introduced. Fracture and fatigue behaviors of aluminum casting alloys are also stated. Increasing the iron content, fracture toughness and fatigue properties (also impact fatigue properties) are degraded. The effect of Ca addition that possesses the modifying effect of the eutectic Si morphology is examined. It has been observed that the harmful effect of iron is largely improved. Increasing the Si content in Al–Si casting alloys, it is generally observed that fatigue strength or ΔKth is increased. Toughness of MMC is generally rather low. Based on the simulation analysis on fracture of Al–SiCW composite, high toughness MMC has been already developed, where some aggregated SiCW granules have been embedded into A6061 matrix. According to FEM analysis, it has been suggested that there is an appropriate aggregation ratio in the granule (i.e. SiCW content in the granule). The above topics have been reviewed.

Titanium Particulate Metal Matrix Composites – Reinforcement, Production Methods, and Mechanical Properties

Abstract: Titanium metal matrix composites (MMCs) offer potential advantages for structural applications, where they combine the high strength, high temperature capability, and oxidation resistance of titanium with an increase in stiffness provided by the ceramic reinforcement. They have the advantage of being isotropic in behaviour, cheaper to manufacture and more amenable to subsequent processing and component forming operations. Of potential reinforcing phases for titanium, mcluding TiB, TiB 2 , SiC, Al 2 O 3 , and TiC, TiB offers the best balance of stiffness, stability, and similarity of thermal expansion coefficients. The methods used to proauce these Ti-TiB MMCs, such as arc melting, gas atomization, mpid solidification, and powder blending have been assessed and the benefits these composites offer over conventional titanium alloys including increased stiffness, good creep performance, fatigue resistance, and wear resistance are highlighted.

Fatigue design procedure for welded hollow section joints

Abstract: Part 1 Recommendations: Scope and general Fatigue design procedures Fatigue strength SCF Calculations for CHS Joints SCF Calculations for RHS Joints.

Effects of warm peening on fatigue life and relaxation behaviour of residual stresses in AISI 4140 steel

Abstract: A new device has been built which allows shot peening in an air blast machine at elevated temperatures. The effects of conventional shot peening and peening at elevated temperatures on the characteristics of regions close to the surface, on the stability of residual stresses and half widths of X-ray interference lines and on the fatigue strength are presented for a quenched and tempered AISI 4140 steel (German grade 42CrMo4). The alternating bending strength is increased by warm peening compared with conventional shot peening. Additional investigations of samples conventionally peened and then annealed confirm that these effects are due to the stability of the dislocation structure, which is highly affected by strain ageing effects. This causes an additional benefit owing to higher stability of the residual stresses induced.

The effect of matrix microstructure on the tensile and fatigue behavior of SiC particle-reinforced 2080 Al matrix composites

Abstract: The effect of matrix microstructure on the stress-controlled fatigue behavior of a 2080 Al alloy reinforced with 30 pct SiC particles was investigated. A thermomechanical heat treatment (T8) produced a fine and homogeneous distribution of S′ precipitates, while a thermal heat treatment (T6) resulted in coarser and inhomogeneously distributed S′ precipitates. The cyclic and monotonic strength, as well as the cyclic stress-strain response, were found to be significantly affected by the microstructure of the matrix. Because of the finer and more-closely spaced precipitates, the composite given the T8 treatment exhibited higher yield strengths than the T6 materials. Despite its lower yield strength, the T6 matrix composite exhibited higher fatigue resistance than the T8 matrix composite. The cyclic deformation behavior of the composites is compared to monotonic deformation behavior and is explained in terms of microstructural instabilities that cause cyclic hardening or softening. The effect of precipitate spacing and size has a significant effect on fatigue behavior and is discussed. The interactive role of matrix strength and SiC reinforcement on stress within “rogue” inclusions was quantified using a finite-element analysis (FEA) unit-cell model.

Fatigue strength of Inconel 718 at elevated temperatures

Abstract: The strength of Inconel 718 under rotary bending fatigue is investigated at room temperature, 300, 500 and 600 °C in air. It is found that in the long-life region, the fatigue strength of a plain specimen is much higher at elevated temperatures than at room temperature, though the static strength decreases with the increase in temperature. The effect of temperature on the fatigue strength is examined in terms of the initiation and early growth behaviour of a small crack. The results are discussed in relation to the competition between the softening of the nickel matrix (γ phase) and the surface oxidation at elevated temperatures.

Lock-in thermography and fatigue limit of metals

Abstract: Thermography was performed on stainless steel 316L and aluminium alloy 7010 samples as they were submitted to a sinusoidal mechanical stress (traction/compression). For each stress amplitude value the temperature data were recorded in 5 s. A specific signal demodulation procedure was used to extract the first two Fourier components and the mean temperature rise. From their particular dependence on the stress amplitude, characteristic stress values could be derived. In some instances, these values are very close to the fatigue limit of the considered material.