Showing papers on "Fatigue limit published in 2007"
TL;DR: A brief overview of the recent progress made in improving mechanical properties of nanocrystalline materials, and in quantitatively and mechanistically understanding the underlying mechanisms is presented in this paper.
994 citations
TL;DR: In this article, the benefits and drawbacks of z-pinning on the interlaminar toughness, damage tolerance and in-plane mechanical properties are compared against other common types of through-thickness reinforcement for composites, such as 3D weaving and stitching.
Abstract: This paper reviews published research into polymer composite laminates reinforced in the through-thickness direction with z-pins. Research into the manufacture, microstructure, delamination resistance, damage tolerance, joint strength and mechanical properties of z-pinned composites is described. Benefits of reinforcing composites with z-pins are assessed, including improvements to the delamination toughness, impact damage resistance, post-impact damage tolerance and through-thickness properties. Improvements to the failure strength of bonded and bearing joints due to z-pinning are also examined. The paper also reviews research into the adverse effects of z-pins on the in-plane mechanical properties, which includes reduced elastic modulus, strength and fatigue performance. Mechanisms responsible for the reduction to the in-plane properties are discussed, and techniques to minimise the adverse effect of z-pins are described. The benefits and drawbacks of z-pinning on the interlaminar toughness, damage tolerance and in-plane mechanical properties are compared against other common types of through-thickness reinforcement for composites, such as 3D weaving and stitching. Gaps in our understanding and unresolved research problems with z-pinned composites are identified to provide a road map for future research into these materials.
630 citations
TL;DR: In this paper, a new processing method was developed for spreading fiber tows to make thin-ply laminated composites, which is robust and easy compared with other available thinply methods.
358 citations
TL;DR: In this paper, material and manufacturing dependent recommendations are given with regard to the course of the SN-curve in the very high-cycle area, where the authors show that a decrease of fatigue strength with increased number of cycles still occurs, even if corrosion or temperature effects are excluded.
343 citations
TL;DR: In this article, a damage model for the simulation of delamination propagation under high-cycle fatigue loading is proposed, based on a cohesive law that links fracture and damage mechanics to establish the evolution of the damage variable in terms of the crack growth rate.
Abstract: A damage model for the simulation of delamination propagation under high-cycle fatigue loading is proposed. The basis for the formulation is a cohesive law that links fracture and damage mechanics to establish the evolution of the damage variable in terms of the crack growth rate dA/dN. The damage state is obtained as a function of the loading conditions as well as the experimentally-determined coefficients of the Paris law crack propagation rates for the material. It is shown that by using the constitutive fatigue damage model in a structural analysis, experimental results can be reproduced without the need of additional model-specific curve-fitting parameters.
339 citations
TL;DR: In this article, the authors defined a theoretical model in order to derive the specific heat loss per cycle from temperature measurements performed during the fatigue test, which was applied to analyze the fatigue strength of smooth and notched specimens made of AISI 304 L stainless steel.
290 citations
TL;DR: In this paper, the effect of fiber orientation on the fatigue strength of a short glass fiber reinforced polyamide-6 has been investigated with tensile and fatigue tests with specimens extracted from injection moulded plates.
242 citations
TL;DR: In this article, the effects of cryogenic treatment on the mechanical properties and microstructures of AISI 4340 steel were investigated, including rotating fatigue, impact and hardness.
229 citations
TL;DR: In this article, the theory of critical distances (TCD) is reformulated in order to make it suitable for predicting fatigue lifetime of notched components in the medium-cycle fatigue regime.
Abstract: In the present paper, the theory of critical distances (TCD) is reformulated in order to make it suitable for predicting fatigue lifetime of notched components in the medium-cycle fatigue regime. This extension of the TCD takes as its starting point the idea that the material characteristic length, L, changes as the number of cycles to failure, N f , changes. In order to define the L versus N f relationship two different strategies were investigated. Initially, we attempted to determine it by using the L values calculated considering material properties defined at the two extremes, namely static failure and the fatigue limit. This strategy, though correct from a philosophical point of view, contained some problems in its practical application. We subsequently attempted to determine the L versus N f relationship by means of two calibration fatigue curves; (one generated by testing plain specimens and the second one generated by testing notched specimens). This second strategy was found to be much more simple to apply to practical problems, resulting in estimations characterized by a higher accuracy. The reliability of the devised method was systematically checked by using experimental results generated by testing notched specimens of low-carbon steel containing different geometrical features and tested using various loading types, stress ratios and specimen thicknesses. The accuracy of the method was further verified by using several data sets taken from the literature. Our method was seen to be successful giving predictions falling always within the scatter band of the data from the parent material. These results are very interesting, especially considering that the TCD is very easy to use because it requires only a linear-elastic stress analysis.
227 citations
TL;DR: In this article, the effect of the FSW process on the microstructure and, consequently, on the tensile and low-cycle fatigue behaviour, of an aluminium matrix (AA7005) composite reinforced with 10.5% of Al2O3 particles (W7A10A).
222 citations
23 Feb 2007
TL;DR: In this article, the authors proposed a method to predict the lifetime of cracks in metal components based on the number of cracks and the amount of cracks formed by the crack propagation process.
Abstract: Foreword. Preface. Symbols and Abbreviations. 1 Introduction. 2 Basic Concepts of Metal Fatigue and Fracture in the Engineering Design Process. 2.1 Historical Overview. 2.2 Metal Fatigue, Crack Propagation and Service-Life Prediction: A Brief Introduction. 2.2.1 Fundamental Terms in Fatigue of Materials. 2.2.2 Fatigue-Life Prediction: Total-Life and Safe-Life Approach. 2.2.3 Fatigue-Life Prediction: Damage-Tolerant Approach. 2.2.4 Methods of Fatigue-Life Prediction at a Glance. 2.3 Basic Concepts of Technical Fracture Mechanics. 2.3.1 The K Concept of LEFM. 2.3.2 Crack-Tip Plasticity: Concepts of Plastic-Zone Size. 2.3.3 Crack-Tip Plasticity: The J Integral. 3 Experimental Approaches to Crack Propagation. 3.1 Mechanical Testing. 3.1.1 Testing Systems. 3.1.2 Specimen Geometries. 3.1.3 Local Strain Measurement: The ISDG Technique. 3.2 Crack-Propagation Measurements. 3.2.1 Potential-Drop Concepts and Fracture Mechanics Experiments. 3.2.2 In Situ Observation of the Crack Length. 3.3 Methods of Microstructural Analysis and Quantitative Characterization of Grain and Phase Boundaries. 3.3.1 Analytical SEM: Topography Contrast to Study Fracture Surfaces. 3.3.2 SEM Imaging by Backscattered Electrons and EBSD. 3.3.3 Evaluation of Kikuchi Patterns: Automated EBSD. 3.3.4 Orientation Analysis Using TEM and X-Ray Diffraction. 3.3.5 Mathematical and Graphical Description of Crystallographic Orientation Relationships. 3.3.6 Microstructure Characterization by TEM. 3.3.7 Further Methods to Characterize Mechanical Damage Mechanisms in Materials. 3.4 Reproducibility of Experimentally Studying the Mechanical Behavior of Materials. 4 Physical Metallurgy of the Deformation Behavior of Metals and Alloys. 4.1 Elastic Deformation. 4.2 Plastic Deformation by Dislocation Motion. 4.3 Activation of Slip Planes in Single- and Polycrystalline Materials. 4.4 Special Features of the Cyclic Deformation of Metallic Materials. 5 Initiation of Microcracks. 5.1 Crack Initiation: Definition and Significance. 5.1.1 Influence of Notches, Surface Treatment and Residual Stresses. 5.2 Influence of Microstructual Factors on the Initiation of Fatigue Cracks. 5.2.1 Crack Initiation at the Surface: General Remarks. 5.2.2 Crack Initiation at Inclusions and Pores. 5.2.3 Crack Initiation at Persistent Slip Bands. 5.3 Crack Initiation by Elastic Anisotropy. 5.3.1 Definition and Significance of Elastic Anisotropy. 5.3.2 Determination of Elastic Constants and Estimation of the Elastic Anisotropy. 5.3.3 FE Calculations of Elastic Anisotropy Stresses to Predict Crack Initiation Sites. 5.3.4 Analytical Calculation of Elastic Anisotropy Stresses. 5.4 Intercrystalline and Transcrystalline Crack Initiation. 5.4.1 Influence Parameters for Intercrystalline Crack Initiation. 5.4.2 Crack Initiation at Elevated Temperature and Environmental Effects. 5.4.3 Transgranular Crack Initiation. 5.5 Microstructurally Short Cracks and the Fatigue Limit. 5.6 Crack Initiation in Inhomogeneous Materials: Cellular Metals. 6 Crack Propagation: Microstructural Aspects. 6.1 Special Features of the Propagation of Microstructurally Short Fatigue Cracks. 6.1.1 Definition of Short and Long Cracks. 6.2 Transgranular Crack Propagation. 6.2.1 Crystallographic Crack Propagation: Interactions with Grain Boundaries. 6.2.2 Mode I Crack Propagation Governed by Cyclic Crack-Tip Blunting. 6.2.3 Influence of Grain Size, Second Phases and Precipitates on the Propagation Behavior of Microstructurally Short Fatigue Cracks. 6.3 Significance of Crack-Closure Effects and Overloads. 6.3.1 General Idea of Crack Closure During Fatigue-Crack Propagation. 6.3.2 Plasticity-Induced Crack Closure. 6.3.3 Influence of Overloads in Plasticity-Induced Crack Closure. 6.3.4 Roughness-Induced Crack Closure. 6.3.5 Oxide- and Transformation-Induced Crack Closure. 6.3.6 &delta K/K max Thresholds: An Alternative to the Crack-Closure Concept. 6.3.7 Development of Crack Closure in the Short Crack Regime. 6.4 Short and Long Fatigue Cracks: The Transition from Mode II to Mode I Crack Propagation. 6.4.1 Development of the Crack Aspect Ratio a/c. 6.4.2 Coalescence of Short Cracks. 6.5 Intercrystalline Crack Propagation at Elevated Temperatures: The Mechanism of Dynamic Embrittlement. 6.5.1 Environmentally Assisted Intercrystalline Crack Propagation in Nickel-Based Superalloys: Possible Mechanisms. 6.5.2 Mechanism of Dynamic Embrittlement as a Generic Phenomenon: Examples. 6.5.3 Oxygen-Induced Intercrystalline Crack Propagation: Dynamic Embrittlement of Alloy 718. 6.5.4 Increasing the Resistance to Intercrystalline Crack Propagation by Dynamic Embrittlement: Grain-Boundary Engineering. 7 Modeling Crack Propagation Accounting for Microstructural Features. 7.1 General Strategies of Fatigue Life Assessment. 7.2 Modeling of Short-Crack Propagation. 7.2.1 Short-Crack Models: An Overview. 7.2.2 Model of Navarro and de los Rios. 7.3 Numerical Modeling of Short-Crack Propagation by Means of a Boundary Element Approach. 7.3.1 Basic Modeling Concept. 7.3.2 Slip Transmission in Polycrystalline Microstructures. 7.3.3 Simulation of Microcrack Propagation in Synthetic Polycrystalline Microstructures. 7.3.4 Transition from Mode II to Mode I Crack Propagation. 7.3.5 Future Aspects of Applying the Boundary Element Method to Short-Fatigue-Crack Propagation. 7.4 Modeling Dwell-Time Cracking: A Grain-Boundary Diffusion Approach. 8 Concluding Remarks. References. Subject Index.
TL;DR: In this article, a microstructure-sensitive crystal plasticity model is used to explicitly model individual grains and polycrystals, which is then used to explore effects of grain size distribution and secondary and tertiary coherent γ′ precipitate size distributions and volume fractions on the cyclic inelastic strain distribution.
Abstract: A computational study is conducted to determine the influence of microstructure attributes and properties on driving forces for fatigue crack formation and microstructurally small crack growth in a polycrystalline Ni-base superalloy, IN100, a turbine disk alloy. A principal objective is to obtain quantitative estimates of the effect of variability of microstructure features on scatter in fatigue life or fatigue strength for a given life. Understanding is sought regarding sensitivity of driving forces to various microstructure attributes that may guide selection of the process route to tailor microstructure to achieve fatigue resistance. A microstructure-sensitive crystal plasticity model is used to explicitly model individual grains and polycrystals, which is then used to explore effects of: (a) grain size distribution and (b) secondary and tertiary coherent γ′ precipitate size distributions and volume fractions on the cyclic inelastic strain distribution. Multiple statistical volume elements (SVEs) are subjected to random periodic boundary conditions to build up statistically significant measures of distributions of cyclic microplasticity. Multiaxial fatigue criteria with critical plane approaches are used to estimate the crack initiation life. Methods are developed for assessing crack formation and microstructurally small crack growth as a function of microstructure attributes.
15 Nov 2007-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the tradeoffs of fatigue crack formation and growth regimes in low cycle and high cycle fatigue, including considerations of effects of notches of various scales, are discussed, and algorithms are summarized for computing nonlocal cyclic plastic shear strain and inferring fatigue resistance, both in terms of mean behavior and variability with microstructure.
Abstract: Further efforts to provide more direct dependence of fatigue life estimation methods on microstructure of alloy systems must consider various factors that are not explicitly addressed by conventional fatigue design tools such as the strain-life curve, the stress-life curve, the modified Goodman diagram, or fatigue limit concepts, or by traditional linear elastic fracture mechanics approaches. In this work, we offer insight from micromechanical perspectives on tradeoffs of fatigue crack formation and growth regimes in low cycle and high cycle fatigue, including considerations of effects of notches of various scales. Relations between remote loading conditions and microstructure-scale cyclic plasticity/crack behavior are considered as a function of stress amplitude and microstructure to support assessment of intrinsic microstructure fatigue resistance (percolation limits for connected microplasticity) as well as effects of extrinsic features such as non-metallic inclusions. Algorithms are summarized for computing nonlocal cyclic plastic shear strain and inferring fatigue resistance, both in terms of mean behavior and variability with microstructure. Several applications are presented, including intrinsic and extrinsic fatigue resistance of Ni-base superalloys, fatigue of polycrystals, cast A356-T6 Al alloy, and fretting fatigue of Ti–6Al–4V.
TL;DR: In this article, fatigue properties of magnesium alloys have been examined on extruded AZ31 bar under uniaxial cyclic loading by both strain and stress controlled conditions adding fatigue tests with mean stresses under stress controlling conditions, fatigue life evaluation method has been discussed along with the analysis of cyclic stress-strain behavior.
TL;DR: There was no difference in flexural strength of uncolored and colored Y-TZP ceramic and the fatigue limit of un colored, FS4 and FS7 zirconia may be defined as lying between 60 and 65% of the stress to failure.
TL;DR: In this paper, the fatigue properties of metallic biomaterials for long-term safe usage of implants in living body such as hip joints, bone plates, and dental implants are investigated.
TL;DR: In this article, the effect of the grain structure produced by hot rolling and equal channel angular pressing on the fatigue behaviour and the bio-corrosion rate were studied for alloy AZ31.
Abstract: Magnesium alloys are considered as candidate materials for temporary implants. Fatigue resistance and controllable rate of corrosion in bodily fluids are essential for such applications. The effect of the grain structure produced by hot rolling and equal channel angular pressing on the fatigue behaviour and the bio-corrosion rate were studied for alloy AZ31. The results suggest that mechanical processing can be used to control both properties.
TL;DR: In this paper, acoustic emission (AE) measurements along the gauge length indicated important critical intra and inter laminar damage occurring as early as 27% of ultimate tensile strength (UTS), typically 0.3% ultimate strain, for laminates with 90° layers.
TL;DR: In this paper, the flexural behaviour of hand manufactured hybrid laminated composites with a hemp natural fibre/polypropylene core and two glass fibres surface layers at each side of the specimen was studied.
Abstract: The present paper studies the flexural behaviour of hand manufactured hybrid laminated composites with a hemp natural fibre/polypropylene core and two glass fibres/polypropylene surface layers at each side of the specimen. When compared with full glass fibres reinforced polypropylene laminates, the hybrid composites have economical, ecological and recycling advantages and also specific fatigue strength benefits. Static and fatigue tests were performed in three point bending for both laminates to evaluate flexural strength properties and fatigue behaviour. Fatigue damage was measured in terms of the stiffness loss. Failure sites and mechanisms were evaluated through microscopy studies and a 3D numerical analysis using finite element method.
TL;DR: In this article, the fatigue properties of four high strength steels with same strength class but containing different inclusion sizes were investigated using an ultrasonic fatigue testing machine in the gigacycle fatigue regime.
TL;DR: In this paper, the experimental results on fatigue resistance of ultra-fine grain metals produced by severe plastic deformation (SPD) are reviewed with regard to two major characteristics of cyclic damage initiation and failure.
Abstract: The experimental results on fatigue resistance of ultra-fine grain metals produced by severe plastic deformation (SPD) are reviewed with regard to two major characteristics of cyclic damage initiation and failure—fatigue limit and fatigue crack growth rate. The fatigue limit benefits considerably from grain refinement down to submicrocrystalline scale. Factors affecting the fatigue limit are discussed in the light of SPD-processing and resultant ultra-fine grain structure. Contrasting with the fatigue limit, the fatigue crack growth threshold deteriorates after SPD in comparison to that of ordinary polycrystals. Possible mechanisms of fatigue crack initiation and propagation are discussed and the guidelines for manufacturing are provided towards enhancement and optimization of fatigue performance.
TL;DR: In this article, a series of experiments has been carried out to characterize the residual tensile and fatigue properties following impact of non-woven hemp fibre mat reinforced polyester, and the degradation of tensile modulus during fatigue cycling has been studied and related to the damage accumulation.
TL;DR: In this paper, the fatigue test results of self-piercing rivet (SPR) joints between similar and dissimilar sheet metals were investigated. And the results indicated that SPR joints have superior fatigue strength than RSW joints for the same material combinations.
TL;DR: In this paper, a light-weight thermoplastic-based fiber-metal laminates were developed based on self-reinforced polypropylene and glass fiber-reined poly-propylene composite materials and an aluminum alloy 2024-T3.
TL;DR: In this paper, the effect of hard anodic oxide and plasma electrolytic oxide coatings on the fatigue strength of 7475-T6 aluminium alloy has been investigated, and the results showed that the reduction in fatigue strength was associated with the development of the tensile residual internal stress within the substrate.
Abstract: The effect of hard anodic oxide and plasma electrolytic oxide coatings on the fatigue strength of 7475-T6 aluminium alloy has been investigated. The coated aluminium alloy was tested using constant load uniaxial tensile fatigue machine. Hard anodising led to an appreciable reduction in the fatigue strength of 7475-T6 alloy of about 75% for a 60 μm thick coating. Further, plasma electrolytic oxidation resulted in reduction of the fatigue strength of about 58% for a 65 μm thick oxide coating. The decrease in fatigue strength of the hard anodic oxide coatings was associated with the stress concentration at the microcracks in the coating. The better fatigue performance of the PEO coatings was attributed to the development of the compressive residual internal stress within the coatings. The reduction in the fatigue strength of the PEO coatings as compared to the uncoated material was associated with the development of the tensile residual internal stress within the substrate. This may cause an early crack initiation in the substrate adjacent to the coating.
TL;DR: In this article, the authors explored the full shape of constant fatigue life (CFL) diagram and developed an efficient CFL diagram-based fatigue life prediction method for multidirectional CFRP laminates.
Abstract: Exploration of a full shape of constant fatigue life (CFL) diagram and development of an efficient CFL diagram-based fatigue life prediction method are attempted for multidirectional CFRP laminates. On three kinds of CFRP laminates of [45/90/−45/0]2s, [0/60/−60]2s and [0/90]3s lay-ups, tension–tension, tension–compression and compression–compression fatigue tests are performed at room temperature for two different stress ratios each. Experimental results clearly show that a stress ratio has a significant influence on the fatigue behavior of those CFRP laminates, and the CFL diagrams delineated using alternating stress and mean stress become asymmetric about the alternating stress axis. The alternating stress component of fatigue load for a given constant value of fatigue life turns maximum in the case of fatigue loading at a critical stress ratio that is nearly equal to the ratio of compressive strength to the tensile one. The shape of CFL diagrams progressively changes from a straight line to a nonlinear curve as a given constant value of fatigue life increases. A new and efficient method for accurately predicting an asymmetric nonlinear CFL diagram is then developed which is based on the static strengths in tension and compression and the reference S–N relationship fitted to the fatigue data for the critical stress ratio. The theoretical CFL diagram constructed following the proposed procedure agrees well with the experimental CFL diagram, regardless of the type of CFRP laminate. It is also demonstrated that the S–N relationships predicted using the proposed CFL diagram-based fatigue life prediction method adequately coincide with the experimental results for fatigue loading with a variety of different stress ratios in the range of fatigue life up to 106 cycles.
TL;DR: In this paper, the effect of z-pinning on the in-plane compression properties and failure mechanisms of polymer laminates is experimentally studied and the reduction to the compression modulus, strength and fatigue performance of carbon/epoxy laminate with increasing volume content and diameter of pins is determined.
TL;DR: In this paper, the Taylor's point method, usually applied to predict fatigue limits of notched components, was used in conjunction with the Modified Wohler Curve Method to formulate a novel fretting fatigue prediction methodology.
TL;DR: In this article, a fatigue test program of a series of small-scale steel beams bonded with a carbon fiber reinforced polymer (CFRP) plate was used to detect crack initiation and monitor crack growth.
TL;DR: In this paper, the effect of pinning on the flexural properties, fatigue life and failure mechanisms of carbon/epoxy laminates was examined and properties changes were discussed in terms of transitions in the dominant failure mechanisms due to the presence of pins.
Abstract: This paper examines the effect of pinning on the flexural properties, fatigue life and failure mechanisms of carbon/epoxy laminates. Five-harness satin weave carbon/epoxy laminates were reinforced in the through-thickness direction with different volume fractions and sizes of fibrous composite pins. Microscopic examination of the laminates before flexural testing revealed that the pins caused considerable damage to the microstructure, including out-of-plane crimping, in-plane distortion and breakage of the fibres and the formation of resin-rich zones around each pin. The pins also caused swelling of the laminate that reduced the fibre volume content. Despite the damage, the pins did not affect the flexural modulus of the laminate. However, increasing the volume content or diameter of the pins caused a steady decline in the flexural strength and fatigue life, which appear to be governed by fiber rupture on the tensile side of the laminate. Property changes are discussed in terms of transitions in the dominant failure mechanisms due to the presence of pins.