Effects of porosity on the fatigue life of polyamide 12 considering crack initiation and propagation
TL;DR: In this article, internal pores in composite materials generated during fabrication processing can induce negative influences on the physical properties, such as fatigue life under repetitive loadings, and the fatigue life of composite materials can be reduced.
Abstract: Internal pores in composite materials generated during fabrication processing can induce negative influences on the physical properties. Among them, the fatigue life under repetitive loadings is on...
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TL;DR: A new software program called ProFatigue is presented as a potentially powerful tool to optimize fatigue testing of implant-supported prostheses, which will contribute to improving the performance of fatigue testing in a more accurate and optimized way, helping researchers to gain a better understanding of the behavior of dental implants in this type of mechanical test.
Abstract: Mechanical complications in implant-supported fixed dental prostheses are often related to implant and prosthetic design. Although the current ISO 14801 provides a framework for the evaluation of dental implant mechanical reliability, strict adherence to it may be difficult to achieve due to the large number of test specimens which it requires as well as the fact that it does not offer any probabilistic reference for determining the endurance limit. In order to address these issues, a new software program called ProFatigue is presented as a potentially powerful tool to optimize fatigue testing of implant-supported prostheses. The present work provides a brief description of some concepts such as load, fatigue and stress-number of cycles to failure curves (S-N curves), before subsequently describing the current regulatory situation. After analyzing the two most recent versions of the ISO recommendation (from 2008 and 2016), some limitations inherent to the experimental methods which they propose are highlighted. Finally, the main advantages and instructions for the correct implementation of the ProFatigue free software are given. This software will contribute to improving the performance of fatigue testing in a more accurate and optimized way, helping researchers to gain a better understanding of the behavior of dental implants in this type of mechanical test.
6 citations
Cites methods from "Effects of porosity on the fatigue ..."
...To provide the progress of the crack size, fatigue tests must be performed on the implant material and crack growth must be registered by using sophisticate experimental techniques, such as potential drop, acoustic emission [44,45]....
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TL;DR: In this article , a power-law-based method was proposed to predict transverse crack accumulation behavior of CFRP cross-ply laminates for evaluation of their remaining life.
Abstract: This study aims to predict the transverse crack accumulation behavior of CFRP cross-ply laminates for evaluation of their remaining life. The tension-tension fatigue tests of CFRP cross-ply laminates were used to investigate the relationship between transverse crack accumulation behavior and the number of cycles of the fatigue tests. We also studied the damage accumulation behavior, including delamination of cross-ply laminates under fatigue loading, and it was indicated that the damage accumulation behavior depends on the maximum load of the fatigue tests. We proposed a method that can predict transverse crack accumulation behavior using a power-law between transverse crack density growth rate and the energy release rate associated with single transverse crack formation. As a result, the proposed method can estimate the applied number of cycles on CFRP cross-ply laminates.
4 citations
TL;DR: The excellent fittings, the physical interpretation of the model parameters and the good expectations to achieve a complete probabilistic analysis of these phenomena justify the interest of the proposed phenomenological approach with possible applications to other cumulative damage processes.
3 citations
TL;DR: In this article , the lifespan of recycled opaque PET has been evaluated throughout tensile-tensile fatigue loading cycles at various steps of the recycling process: the specimens are obtained from flakes after grinding PET wastes (F-r-OPET), from a subsequent homogenization step (r-opET-hom) and after reactive extrusion (Rex-r.OPET).
Abstract: Polyethylene terephthalate (PET) is among the most used thermoplastic polymers in large scale manufacturing. Opaque PET is increasingly used in milk bottles to save weight and to bring a glossy white aspect due to TiO2 nanoparticles. The recyclability of opaque PET is an issue: whereas the recycling channels are well established for transparent PET, the presence of opaque PET in household wastes weakens those channels: opaque bottles cannot be mixed with transparent ones because the resulting blend is not transparent anymore. Many research efforts focus on the possibility to turn opaque PET into resources, as one key to a more circular economy. A recent study has demonstrated the improvement of the mechanical properties of recycled PET through reactive extrusion. In the present work, the lifespan of recycled opaque PET has been evaluated throughout tensile–tensile fatigue loading cycles at various steps of the recycling process: The specimens are obtained from flakes after grinding PET wastes (F-r-OPET), from a subsequent homogenization step (r-OPET-hom) and after reactive extrusion (Rex-r-OPET). Virgin PET is also considered as a comparison. First, tensile tests monitored by digital image correlation have been carried out to obtain the elastic modulus and ultimate tensile stress of each type of PET. The fatigue properties of reactive REx-r-OPET increase, probably associated with the rise of cross-linking and branching rates. The fatigue lifespan increases with the macromolecular weight. The fracture surface analysis of specimens brings new insight regarding the factors governing the fatigue behavior and the damaging mode of recycled PET. TiO2 nanoparticles act as stress concentrators, contributing to void formation at multiple sites and thus promoting the fracture process. Finally, the fatigue life of REx-r-OPET is comparable to those of virgin PET. Upcycling opaque PET by reactive extrusion may be a relevant new route to absorb some of the growing amounts of PET worldwide.
2 citations
08 Feb 2013
TL;DR: In this paper, the Wöhler curve approach to fatigue life assessment is extended to include variable amplitude loads with mean value influence, which is done through the definition of an equivalent load amplitude, which depends both on the usual damage accumulation hypothesis and on some mean value correction model.
Abstract: The Wöhler curve approach to fatigue life assessment is here extended to include variable amplitude loads with mean value influence. This is done through the definition of an equivalent load amplitude, which depends both on the usual damage accumulation hypothesis and on some mean value correction model. The method is exemplified by using the Gerber model, the mean stress sensibility model and different parametrisations of the crack closure model. All models are applied to three different data sets, including aluminium, welded steel, and cast steel specimens subjected to different spectrum loads. The results are interpreted in relation to the complexity of the different models and the trade off between complexity, number of tests and random scatter is discussed in the context of prediction uncertainty. Introduction In industrial practice the Wöhler curve is the main design tool for fatigue life. However, the concept of Wöhler curve design varies over different applications. In the simplest case, the strength of a component is determined by laboratory tests at constant amplitude by estimating one or two parameters, and service loads are predicted by some variant of equivalent stress ranges, usually based on the Palmgren-Miner cumulative fatigue hypothesis. On the other hand, fatigue is known to be a very complex phenomenon, and a model close to reality should include not only the Wöhler parameters, but also for instance the local mean stresses, the yield stress, crack closure and threshold characteristics, the defect contents, or the grain size. However, these features may not be known to the engineer, at least not in the design stage, and therefore most of these must be excluded in engineering practice. In the case of empirical or semi-empirical modeling, where parameters are fitted from experimental results, there is a clear trade off between model complexity and knowledge about influentials that can be studied in mathematical terms. In this paper we will demonstrate this by studying the problem of including the mean stress influence in the simple Wöhler concept. We start at a method of predicting fatigue life at variable amplitude using the concept of an equivalent stress range presented in Johannesson et al. [1]. The Palmgren-Miner hypothesis in combination with the Basquin equation leads to the following predicted life β α ˆ ˆ − ⋅ = eq pred S N ,
1 citations
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TL;DR: In this paper, an integral is exhibited which has the same value for all paths surrounding a class of notches in two-dimensional deformation fields of linear or non-linear elastic materials.
Abstract: : An integral is exhibited which has the same value for all paths surrounding a class of notches in two-dimensional deformation fields of linear or non-linear elastic materials. The integral may be evaluated almost by inspection for a few notch configurations. Also, for materials of the elastic- plastic type (treated through a deformation rather than incremental formulation) , with a linear response to small stresses followed by non-linear yielding, the integral may be evaluated in terms of Irwin's stress intensity factor when yielding occurs on a scale small in comparison to notch size. On the other hand, the integral may be expressed in terms of the concentrated deformation field in the vicinity of the notch tip. This implies that some information on strain concentrations is obtainable without recourse to detailed non-linear analyses. Such an approach is exploited here. Applications are made to: Approximate estimates of strain concentrations at smooth ended notch tips in elastic and elastic-plastic materials, A general solution for crack tip separation in the Barenblatt-Dugdale crack model, leading to a proof of the identity of the Griffith theory and Barenblatt cohesive theory for elastic brittle fracture and to the inclusion of strain hardening behavior in the Dugdale model for plane stress yielding, and An approximate perfectly plastic plane strain analysis, based on the slip line theory, of contained plastic deformation at a crack tip and of crack blunting.
7,468 citations
5,772 citations
"Effects of porosity on the fatigue ..." refers methods in this paper
...Paris law correlating da/dN with ΔK has been applied to a number of studies [25–28] as a reliable lifetime prediction model ever since it was proposed [29] although it has limitations in accounting for unstable crack propagation regime, the effect of stress ratio, and crack closure [28]....
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Book•
01 Jan 2000
TL;DR: The Stress Analysis of Cracks Handbook as mentioned in this paper provides a comprehensive, easy-to-access collection of elastic stress solutions for crack configurations, along with other relevant information, such as displacements, crack opening areas, basic stress functions source references, accuracy of solutions, and more.
Abstract: Nearly double the size of the previous edition, the third edition of this classic reference provides a comprehensive, easy-to-access collection of elastic stress solutions for crack configurations. For each configuration, The Stress Analysis of Cracks Handbook present crack tip stress intensity formulas along with other relevant information, such as displacements, crack opening areas, basic stress functions source references, accuracy of solutions, and more. Throughout, it stresses formulas for application to test configurations. The introductory section details the methods of developing the informatio A series of appendices represents special methods and special applications. Now in a hardbound format, the current Handbook offers a number of new features including: * Ne Stress Solutions * Cracked Configurations * Plates with Pinching Loads * Dislocations and Cracks Solutions * Plastic Zone Instability (Expanding a Potentially Interceding "Elastic" Failure Mechanism) * Estimation Methods for Stress Intensity Formulas * J-Integral Methods * Pure Shear Plasticity Solutions. The authors provide 30 new solution pages, plus modifications of older solutions. Contents Include: * Introductory Information Stress Analysis Results for Common Test Specimen Configurations with Cracks * Cracks Along a Single Line * Parallel Cracks * Cracks and Holes or Notches * Curved, Angled, Branched, or Radiating Cracks * Cracks in Reinforced Plates * Three-Dimensional Cracked Configurations * Crack(s) in a Rod or a Plate by Energy Rate Analysis * Strip Yield Model Solutions * Cracks(s) in a Shell * Appendices.
5,374 citations
"Effects of porosity on the fatigue ..." refers background in this paper
...The fracture mechanics-based approach needs simplified formulae of the stress intensity factor, which are often provided in standard handbooks [24]....
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03 Mar 2017
TL;DR: Fracture Mechanics: Fundamentals and Applications, Fourth Edition as discussed by the authors is the most useful and comprehensive guide to fracture mechanics available It has been adopted by more than 150 universities worldwide and used by thousands of engineers and researchers.
Abstract: Fracture Mechanics: Fundamentals and Applications, Fourth Edition is the most useful and comprehensive guide to fracture mechanics available It has been adopted by more than 150 universities worldwide and used by thousands of engineers and researchers This new edition reflects the latest research, industry practices, applications, and computational analysis and modeling It encompasses theory and applications, linear and nonlinear fracture mechanics, solid mechanics, and materials science with a unified, balanced, and in-depth approach Numerous chapter problems have been added or revised, and additional resources are available for those teaching college courses or training sessions Dr Anderson’s own website can be accessed at wwwFractureMechanicscom
5,035 citations
"Effects of porosity on the fatigue ..." refers background in this paper
...Therefore, concepts such as energy-based energy release rate [45], stress-based J-integral [46], and displacement-based crack tip opening displacement (CTOD) [45] have been proposed....
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01 Jul 1943
TL;DR: In this paper, a simple formula is suggested for describing the stress-strain curve in terms of three parameters; namely, Young's modulus and two secant yield strengths.
Abstract: A simple formula is suggested for describing the stress-strain curve in terms of three parameters; namely, Young's modulus and two secant yield strengths. Dimensionless charts are derived from this formula for determining the stress-strain curve, the tangent modulus, and the reduced modulus of a material for which these three parameters are given. Comparison with the tensile and compressive data on aluminum-alloy, stainless-steel, and carbon-steel sheet in NACA Technical Note No. 840 indicates that the formula is adequate for most of these materials. The formula does not describe the behavior of alclad sheet, which shows a marked change in slope at low stress. It seems probable that more than three parameters will be necessary to represent such stress-strain curves adequately.
2,473 citations
"Effects of porosity on the fatigue ..." refers methods in this paper
...Material parameters required for Morrow’s model can be determined by curve fitting of the elastoplastic stress–strain curve using simplified constitutive model such as Ramberg-Osgood model [15]....
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