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.

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Optimized Planning and Evaluation of Dental Implant Fatigue Testing: A Specific Software Application.

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.

Prediction of transverse crack multiplication of CFRP cross-ply laminates under tension-tension fatigue load

A methodology for phenomenological analysis of cumulative damage processes. Application to fatigue and fracture phenomena

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.

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Evaluation of Fatigue Life of Recycled Opaque PET from Household Milk Bottle Wastes

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 ,

Mean value influence in fatigue - on the rational choice of model complexity

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...

Youn Jun Kim

Papers

Effects of porosity on the fatigue life of polyamide 12 considering crack initiation and propagation