Evaluation Of Fatigue Behavior Research Articles

Optimization of Mechanical Properties and Evaluation of Fatigue Behavior of Selective Laser Sintered Polyamide-12 Components.

In this paper, a comprehensive study of the mechanical properties of selective laser sintered polyamide components is presented, for various different process parameters as well as environmental testing conditions. For the optimization of the static and dynamic mechanical load behavior, different process parameters, e.g., laser power, scan speed, and build temperature, were varied, defining an optimal parameter combination. First, the influence of the different process parameters was tested, leading to a constant energy density for different combinations. Due to similarities in mechanical load behavior, the energy density was identified as a decisive factor, mostly independent of the input parameters. Thus, secondly, the energy density was varied by the different parameters, exhibiting large differences for all levels of fatigue behavior. An optimal parameter combination of 18 W for the laser power and a scan speed of 2666 mm/s was determined, as a higher energy density led to the best results in static and dynamic testing. According to this, the variation in build temperature was investigated, leading to improvements in tensile strength and fatigue strength at higher build temperatures. Furthermore, different ambient temperatures during testing were evaluated, as the temperature-dependent behavior of polymers is of high importance for industrial applications. An increased ambient temperature as well as active cooling during testing was examined, having a significant impact on the high cycle fatigue regime and on the endurance limit.

Performance evaluation of fatigue behavior in extrusion-based functionally graded materials

Performance evaluation of fatigue behavior in extrusion-based functionally graded materials

Fatigue life analysis and damage evaluation in glass fiber reinforced composite materials based on recycled polyethylene terephthalate

Viability of recycling polyethylene terephthalate (PET) can be enhanced by increasing its usage as a matrix material in manufacturing of composite materials. Structural applications of composite materials almost always involve fatigue loading and evaluation of fatigue behaviour is essential to explore the full potential of composite materials based on recycled PET. With an aim to increase the acceptability of recycled PET based resins, fatigue performance of glass fiber reinforced composite materials based on unsaturated polyester resin derived from recycled PET (rPET-UPR) has been evaluated in the present research. Glass fiber composites laminates of stacking sequence [0/(±45)2/0]T have been fabricated using vacuum infusion process. Fatigue tests were performed at the stress ratio of 0.1, where the stress level varied from 40%–80% of the ultimate tensile strength (UTS). The results of fatigue tests show that the fatigue lives of composites based on rPET-UPR were lower as compared to virgin polyester matrix composites. However, Statistical analysis of the fatigue life data using two parameter Weibull distribution, established that there is no deleterious effect on the scatter observed in fatigue lives of these composites, as compared to composites based on virgin polyester resin. Due to higher degradation of rPET-UPR matrix as well as weak interfacial properties, 13% higher self generated temperature was observed during fatigue loading in comparison to virgin resin based composite materials. A three phase stiffness degradation curve has been observed for these composite materials indicating stiffness loss in the range of 20%–35% till the time of failure, which correlates well with the experimental damage observations. A nonuniform and rapid damage growth was observed at high-stress levels, whereas a more uniform damage zone was observed at the low-stress levels.

Dissimilar Welding Applications and Evaluation of Fatigue Behaviour of Welded Jo ints: An Overview

Dissimilar Welding Applications and Evaluation of Fatigue Behaviour of Welded Jo ints: An Overview

Fatigue behavior evaluation of full-scale OSD-UHPC composite bridge deck system

To investigate the fatigue performance and fatigue damage process of the Orthotropic Steel Deck (OSD) - Ultra-High Performance Concrete (UHPC) composite bridge deck, a two-span continuous full-scale specimen was designed and tested under cyclic loading. Test results showed that the fatigue cracks firstly initiated near the lower part of the weld toe of the rib-to-cross beam welded joint, and then cracks along the weld length of the U-rib butt-welded joint developed. These observations followed by the OSD-UHPC interface debonding. The U-rib bolted joint exhibited better fatigue resistance than the U-rib butt-welded joint. The S-N curves of the rib-to-cross beam welded joint, the U-rib butt-welded joint and the U-rib bolted joint were established based on existing fatigue test data, and were compared with provisions in design codes. The S-N curves from the beam test for the short-headed stud connectors were compared with that from the push-out test. And the established S-N curves with 95% survival probability from the push-out test could be used to assess the global fatigue performance of the composite deck. Considering the durability-based critical crack width of UHPC, the established tensile S-N curve regarding critical UHPC crack width of 0.05 mm could be used to evaluate the anti-fatigue cracking ability of the UHPC layer in the composite deck system.

Efficiency of 3D printed composite resin restorations compared with subtractive materials: Evaluation of fatigue behavior, cost, and time of production

Statement of problemThree-dimensionally (3D)-printed composite resins have been marketed as materials for definitive restorations. However, limited information is available regarding the stability of the adhesive interface and the efficiency of 3D printed composite resins. PurposeThe purpose of this in vitro study was to evaluate the integrity of the marginal adhesive interface before and after thermal and mechanical fatigue of an initial formulation of a 3D printed composite resin and to evaluate the efficiency of this manufacturing method. Material and methodsFreshly extracted molars were prepared for onlays and adhesively restored with either 3D printed composite resin (VarseoSmile Crown Plus) (Group 3D), milled composite resin (Tetric CAD) (Group MCOMP), milled PMMA (Telio CAD) (Group PMMA), and milled lithium disilicate (IPS e.max CAD) (Group EM). Marginal analysis was performed under a scanning electron microscope before and after fatigue by thermomechanical cyclic loading, and initial and terminal percentages of continuous margin (%CM) were compared. The time required for the production of each type of restoration was recorded, and the production costs were also compared. ResultsBefore aging, 3D, MCOMP, and EM presented comparable values of %CM (69.8%, 75.9%, and 63.1%, respectively) that were statistically significantly higher (P<.05) than those of PMMA (45.1%). After aging, 3D and EM had comparable results (44.7% and 43.7%, respectively), which were lower than those of the MCOMP group (68.5%) but higher than those of the PMMA group (20.5%). Regarding time efficiency, 3D printing took less time than MCOMP or PMMA if more than 8 restorations were fabricated. For the production costs, 3D printing was 5.5, 8.7, and 10.2 times less expensive than PMMA, MCOMP, and EM, respectively. The initial equipment cost was also lower for the additive manufacturing method. However, 3D printing did not always considerably reduce waste. ConclusionsIn terms of marginal adaptation, the evaluated initial formulation of a 3D printed composite resin behaved similarly to other well-established definitive restoration materials and better than milled PMMA, both before and after fatigue. Three-dimensionally printed resins present advantages in terms of equipment and consumable costs, even for a single restoration, but also for production time when more than 8 restorations were fabricated.

Stochastic analysis on fatigue life of butt-welded joints with uneven thickness considering mean stress effects

With the wide application of steel structure buildings and bridges, the fatigue of welded connections has gradually become a research upsurge. Accurate evaluation of fatigue behavior is the most challenge issue for the study of fatigue failure of welded structures. In this paper, the conventional S-N curve was calculated by Bayesian method, and compared with several standards and probability models, such as EN1993-1-9, IIW-1823-07, ASTM E739 and Weibull distribution model etc. To consider the influence of load ratio R reflecting mean stress on fatigue life, using Bayesian method and S-N-R model, the design fatigue life of the welded joints was successfully calculated.

Evaluation of Fatigue Behavior and Surface Characteristics of Novel Machining Process: Rotary Chemical Machining (RCM)

In this study, Rotational Chemical Machining (RCM) as a novel machining process is introduced. The properties such as surface roughness and residual stress as well as fatigue strength of the RCM process are evaluated, discussed and compared to the conventional turning process. In this sense, Scanning Electron Microscope (SEM) and Atomic Force Microscope (AFM) were utilized. The results show the superiority of the RCM method over the conventional method and eliminate limits of process such as low surface quality and improve fatigue strength. The Amplitude Distribution Curve has a balanced Gaussian shape in RCM indicating the balanced distribution of peaks and valleys on machined surface. Due to the absence of machining force in the RCM process, in comparison to the turning process, maximum residual stress is significantly decreased from 363Mpa to 71Mpa; surface roughness reduced from 3.1µm to 1.5 µm as well as the fatigue strength improved 20% approximately.

Comprehensive evaluation of electrocaloric effect and fatigue behavior in the 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 bulk relaxor ferroelectric ceramic

Electrocaloric refrigeration shows potential as a viable alternative to vapor-compression and/or thermo-electric refrigeration. One of the main challenges that need to be addressed in electrocaloric technology is the fatigue behavior of electrocaloric materials, in terms of both structural and functional aspects. Here, a comprehensive evaluation of the fatigue behavior of the 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 (PMN-10PT) bulk relaxor ferroelectric (or shortly relaxor) ceramic at room temperature is performed. First, the temperature-change dependence on the slew rate was studied. It is shown that the adiabatic conditions are well approached at the slew rate above 1 kV s−1, at which the adiabatic temperature change of 1.3 K was measured at the electric field change of 90 kV cm−1. Then, the durability limits (i.e., the fatigue life) of ten PMN-10PT samples were investigated during unipolar electric field cycling. The results showed that the material could withstand up to 106 cycles at the electric field change of 90 kV cm−1 with only minor degradation of the functional properties (less than 5% of the maximum adiabatic temperature change). Hence, PMN-10PT can be considered as a promising material for use in an electrocaloric cooling device, but some critical issues that caused premature failure of several samples would need to be further addressed and improved.

High-Strain Low-Cycle Fatigue Behavior of Thermomechanically Treated Rebar

Low-cycle fatigue (LCF) behavior of a thermomechanically treated Fe 500 grade rebar has been evaluated under high-strain ranges to understand its seismic performance. The total strain-controlled LCF tests have been performed at five different strain (1.0, 2.0, 3.0, 4.0 and 5.0%) ranges at ambient temperature until failure maintaining a constant true strain rate of 1 × 10−3 s−1 and a fixed strain ratio of − 1. Fatigue data have been analyzed following strain-life relationship; while, macro- and micro-features of the failed specimens have been critically examined under SEM. Evaluation of fatigue behavior has been supplemented by microstructural characterization apart from measurements of hardness and tensile property. Continued cyclic softening has been observed till failure, and the cyclic yield strength is found to be significantly lower than the monotonic one. Cross-sectional microhardness measurements of rebar before and after fatigue reveals significant reduction in hardness specifically in the rim region with tempered martensite microstructure. The strain-life relationship accurately predicts the cyclic plastic behavior of the selected rebar which also exhibits non-Masing behavior. The fatigue crack is always found to initiate from the transverse rib root and propagates along the rim region following the rib.

Evaluation of Fatigue Behavior of Epoxy Coatings used for Potable Water Storage Tanks

In this paper, three types of epoxy-based coatings (Polyamide, pure Polyamine, and Polyamine reinforced by glass-flake) used as a lining for potable water tanks were studied using experimental and finite element methods. Tensile, impact, and fatigue tests were conducted on uncoated and coated AISI 316 stainless steel. The test results show that the applied epoxy based coating improves the mechanical properties, increases of fatigue crack resistance, and enhance the dynamic fracture toughness. The fatigue crack propagation is influenced by the compositions of epoxy coating, and the glass-flake improves the coating resistance to fatigue crack propagation compared to other types.

Tribological functionalization of titanium alloys by Micro-Arc Oxidation for marine applications

Micro-arc Oxidation (MAO) process is a plasma assisted electrochemical process, which allows formation of ceramic-like dry oxides on top of light alloys surfaces. The good corrosion resistance as well as the low density of titanium alloys are recognized and so required for conception of structural parts in marine environment. However, their tribological behaviour reveals an important tendency to stick-slip phenomenon, which makes use of these alloys for dynamic contact mechanisms difficult. Through the MAO project from IRT M2P, formation of a MAO coating composed of aluminium titanate has been investigated to improve tribological behaviour of a commercially pure titanium (Grade 2) and an α+β alloy (TA6V, Grade 5). Pin-on-disc testing has been carried out to evaluate friction coefficient and the presence or not of stick-slip phenomenon in various contact configurations (involving non-treated titanium surfaces, MAO treated surfaces, with steel or titanium balls …) in dry or artificial seawater media. Those test campaigns are completed by evaluation of fatigue behaviour, and tribological testing on a demonstrator. Finally, this study highlights influence of MAO coating on diminishing (to removed) stick-slip phenomenon, accompanied by a reduction of friction coefficient, whatever the kind of contact (single treated surface or both ones) and the medium.

Experimental evaluation of fatigue behaviour of thin Al5456 welded joints

AbstractBecause of wide applications of welded structures in different industries, using design codes and standards such as IIW recommendations is known as a safe and common method to design welded joints. The weld geometry and thickness of welded joint are the most important parameters that affect the fatigue strength of welded joints. In the present study, the fatigue behaviour of thin Al5456 butt‐welded joints has been investigated, and the effect of thickness on fatigue strength has been evaluated. Contrary to the above‐mentioned recommendations about thin welded joints, it was shown that the thickness of welded joints affects the fatigue strength. Moreover, the fatigue test results have been compared with the IIW design recommendations for three well‐known approaches in order to analyse the reliability of the codes. According to the design stress‐life diagrams, it was found that in some cases, the fatigue strength has much larger values than the IIW predictions, and IIW‐based design causes an over conservative design. While in some other cases, the fatigue strength is lower than IIW recommendations, and it leads to a non‐conservative design. Based on the experimental results, the new values for slope of S‐N curve and FAT have been proposed in order to improve the design diagrams.

Simulation of Ti-6Al-4V cruciform welded joints subjected to fatigue load using XFEM

The stress distribution of cruciform shape welded joints is analyzed by finite element codes ABAQUS. Welded joints with various weld shapes and sizes are investigated to estimate the fatigue life of different joints. The fatigue behavior is evaluated under constant amplitude loading (R=0.1). The aim of this work is fatigue behavior evaluation of fillet welded cruciform joint for different weld geometry. The weld geometry are considered: concave, convex and flat weld shape of different weld sizes. The stress intensity factor (SIF) of a TI 6AL4V, is calculated by using Extended finite element method (XFEM) in ABAQUS software. Simulations of fatigue life for different weld shapes at different stresses are analyzed and crack initiations are identified the number of severe fatigue life cycles which are obtained are very close to the theoretical values. In present study the importance of XEFM method is recognized to predict the crack growth rate for convex specimen which is subjected maximum fatigue stress.

Evaluation of fatigue behavior of asphalt binders containing reclaimed asphalt binder using simplified viscoelastic continuum damage approach

Several fatigue damage analysis approaches have been introduced for asphalt binders and mixtures. In this study, using three modifiers including softer bitumen, a rejuvenator and waste polymer modified bitumen, fatigue behavior of RAB-containing binder mixes was evaluated based on the simplified viscoelastic continuum damage mechanics (S-VECD). In addition, correlations between the S-VECD parameters and the other fatigue failure criteria were investigated. For this purpose, the time sweep test was used to evaluate fatigue behavior of various asphalt binders in controlled-strain mode. Results showed that the rejuvenator and softer bitumen had the greatest effect in terms of prioritization on the improvement of the fatigue resistance of the RAB-containing binder mixes. Moreover, the results showed that good unique relationships between plateau value (PV) and Nf50 and between rate of change of total released pseudo strain energy (GR) and Nf50 were established in the RAB-containing binder mixes. Furthermore, there was a good relationship between the two concepts of the dissipated energy approach used for determination of the PV and the dissipated pseudo strain energy approach which used for calculation of the GR values.

Evaluation of fatigue behavior of high reclaimed asphalt binder mixes modified with rejuvenator and softer bitumen

Reclaimed asphalt binder (RAB) is aged bitumen extracted from milling of deteriorated asphalt pavement materials. The objective of this study was to analyze the effect of a new rejuvenator as well as softer bitumen on regenerating fatigue characteristics of the RAB-containing binder mixes as compared to the virgin (control) binder. In this study, firstly fatigue resistance of binder mixes containing different percentages of RAB was evaluated by temperature sweep, linear amplitude sweep (LAS) and time sweep tests. Secondly, correlations between different fatigue test methods were established. Results showed that use of rejuvenating agent improved fatigue performance of binder mixes containing up to 100% RAB to the level of that of the control binder. On the other hand, the softer bitumen improved fatigue behavior of asphalt binders containing up to 50% RAB in comparison with the control binder. Based on the obtained results, the current fatigue Superpave criteria (G∗.sinδ) correlated well with parameter B (LAS parameter). In addition, the fatigue lives obtained from the LAS test have good correlation with strains at peak stress in stress-strain curve. Furthermore, Results indicated that there was a fair agreement between fatigue lives obtained using the LAS and the time sweep tests.

Evaluation of Fatigue Behavior in Dental Implants from In Vitro Clinical Tests: A Systematic Review

In the area of dentistry, there is a wide variety of designs of dental implant and materials, especially titanium, which aims to avoid failures and increase their clinical durability. The purpose of this review was to evaluate fatigue behavior in different connections and implant materials, as well as their loading conditions and response to failure. In vitro tests under normal and dynamic loading conditions evaluating fatigue at implant and abutment connection were included. A search was conducted in PubMed, Scopus, and Science Direct. Data extraction was performed independently by two reviewers. The quality of selected studies was assessed using the Cochrane Handbook proposed by the tool for clinical trials. Nineteen studies were included. Fourteen studies had an unclear risk and five had high risk of bias. Due to the heterogeneity of the data and the evaluation of the quality of the studies, meta-analysis could not be performed. Evidence from this study suggests that both internal and morse taper connections presented a better behavior to failure. However, it is necessary to unify criteria in the methodological design of in vitro studies, following methodological guidelines and establishing conditions that allow the homogenization of designs in ISO (International Organization for Standardization) standards.

A unifying energy approach for high cycle fatigue behavior evaluation

The purpose of this paper is to develop a unifying energy approach for rapid assessment of fatigue parameters in high-cycle fatigue regime. The energy dissipation is considered as an index of fatigue damage to analyze the progressive microstructural movements and to evaluate the fatigue behavior of low-carbon steel (e.g. residual life and microplasticity). A set of theoretical and experimental works are performed to demonstrate its applicability. The relationships between the predicted fatigue parameters and the traditional testing results are compared and discussed. It is concluded that the present approach is applicable for macro and micro high-cycle fatigue behavior evaluation.

Dynamic modeling of wind turbines. Experimental tuning of a multibody model

This work is part of a research project funded by the Italian Ministry of the University and Research (MIUR), under the call for "National Interest Research Projects 2015 (PRIN 2015)", titled "Smart Optimized Fault Tolerant WIND turbines (SOFTWIND)".Within this project, the research unit of the University of Perugia (UniPG) aims to develop dynamic modeling and simulation methodologies and fatigue behavior evaluation ones for wind turbine as a whole. The development of these methodologies will be aimed at predicting the life of generic wind turbines, also providing important and fundamental parameters for optimizing their control, aimed at reducing the failures of these machines.In the present paper, a small turbine, developed at the Department of Engineering of the University of Perugia, will be analyzed. The multibody modeling technique adopted and the experimental activity conducted in the wind tunnel of UniPG, needed for the tuning of the model, will be described.The analysis of both model behavior and experimental data has allowed for the definition of a robust multibody modeling technique that adopts a freeware code (NREL - FAST), universally considered to be a reference in this field.The goodness of the model guarantees the capabilities of the simulation environment to analyze the real load scenario and the fatigue behavior of this kind of device.

P92 and 15CH2NMFA Steels – A Comparison of Fatigue Characteristics obtained on standard and miniature test specimens

In this paper, the results of the fatigue tests of the P92 and 15CH2NMFA steels are presented and discussed. The fatigue S – N curves were obtained by means of both standard and miniature test specimens. The Small Fatigue Test (SFT) specimens were manufactured partially by machining and also by waterjet cutting.The fatigue tests were performed on Amsler 10 HFP 5100 ZWICK//Roell high-frequency pulsator at room temperature and R = 0,1 and R = -1 cycle asymmetries. The results obtained on standard and SFT specimens are compared and in case of P92 steel are also compared the two methods of SFT specimens manufacturing.In case of 15CH2NMFA steel, the results of standard and SFT specimens are in a very good agreement both within the time limit fatigue range and the fatigue limit. After taking the stress concentration of SFT specimens into consideration, the results of traditional fatigue test samples and SFT samples are similar.In case of P92 steel, the leaning branch of S-N curves is much steeper for SFT specimens and the fatigue limits lower than it could be expected after the stress concentration is taken into account. The fatigue limits for equal cycle asymmetry show the same ratio of standard to SFT fatigue limits, for R = 0,1 it is 1,31, for R = 1 it is 1,32. This very good agreement can be used for the evaluation of fatigue behaviour of P92 steel by means of SFT specimens.The comparison of the two ways of SFT samples manufacturing revealed a scatter of fatigue test results, nevertheless the fatigue limits differ by 5 MPa only, so that even the influence of the manufacturing seems to be negligible.