Fatigue Properties Of Materials Research Articles

Fatigue of Cellulose Acetate and Ductile Metals

By a theoretical consideration of a viscous body it has been deduced a formula for the description of the fatigue properties of ductile metals and plastic materials. This formula has been compared with experimental fatigue data of Wöhler-curves (S-N curves). For cellulose acetate, iron, copper, nickel, silver, zinc and, to a restricted degree, also for aluminum a sufficient accordance between the experimental data and the theoretical curves has been reached. With this procedure it is possible to determine fatigue limits for these materials. Similar results are obtained for the creep of brass. It is supposed that the cause of the fatigue limit is the near surface stress of the specimen.

Biomechanical behavior of extra-narrow implants after fatigue and pull-out tests

Statement of problemNarrow implants have limited indications, and implant fracture may occur when these indications are not followed. PurposeThe purpose of this in vitro study was to investigate the mechanical behavior of a 2.9-mm–diameter implant using a fatigue limit test and to investigate the Morse effect of 2 different Morse taper systems, 2.9-mm–diameter (FAC group) and 3.75-mm–diameter (CM group) implants, using a pull-out test. The null hypothesis was that the tensile strengths of the components for both systems would be similar. Material and methodsThe fatigue properties of 13 specimens under 6 loads were determined. The test was performed at 15 Hz and for 5×106 cycles. In the pull-out test, the specimens were divided into 2 groups (n=8), the FAC group (2.9-mm–diameter) and the CM group (3.75-mm–diameter). Statistical analysis for the pull-out test was performed with the Student t test (α=.05). ResultsThirteen specimens underwent the fatigue test. Only 5 did not fail when subjected to the frequency and number of cycles examined. Three of the specimens did not fail under a load of 130 N. The pull-out test showed a significant difference between the FAC and CM groups (P<.001). ConclusionsAccording to the fatigue test, the extra-narrow implant (Facility; Neodent) was compatible with the low masticatory effort regions, as indicated by the manufacturer. The better performance of the FAC group in the pull-out test may be due to its design, which promotes the pure Morse effect in the implant-abutment interface, and the angulation of its internal conical portion.

Fatigue characterization of a beam-to-column riveted joint

Fatigue failures are a concern for old riveted steel bridges since most of them were not originally designed taking into account fatigue. The usual fatigue assessment approach for riveted joints consists of using the fatigue class 71 S-N curve proposed in Eurocode 3, part 1–9. However, this approach may lead to excessive conservative predictions since it is applied indistinctly for different riveted connection geometries and materials. Riveted joints fatigue classification according to the proposal of Taras and Greiner produce more consistent description of the experimental data rather than the Class 71 S-N curve as proposed in the EC3. Local approaches are an alternative methodology to perform fatigue characterization of any type of joints, made of any material, providing that material fatigue properties are available as well as accurate numerical models of the joints. This paper presents an experimental campaign and a numerical analysis concerning down-scale riveted specimens. The fatigue behaviour of these riveted joints was also modelled using standard and extended finite element methods. The different models produced diverse predictions, depending on the failure modes considered.

Experimental validation of an ANN model for random loading fatigue analysis

The use of artificial intelligence especially based on artificial neural networks (ANN) is now prevalent in many fields of data analysis and interpretation. There have been a number of papers published in the literature on the use of ANN for fatigue characterisation. Most of these have however been developed for rather focussed application with limited capability for fatigue life prediction for a broad scope of material and loading conditions. The authors recently presented a uniquely generalised ANN model that is capable of making fatigue life prediction for a broad range of material fatigue properties and loading spectral forms. The model was developed using simulated data albeit subject to conceivable constraints between possible materials properties and load forms. This paper presents a validation of the ANN model using a Society of Automotive Engineers (SAE) random fatigue loading experimental test data. The capabilities and potentials of the model are demonstrated by comparison with the SAE random load fatigue test results and with results obtained from other predictive methods. The performance of the ANN is highly encouraging as a general tool for random loading fatigue analysis.

Effect of Shot Peening and Solidification on Fatigue Properties of Epoxy Base Composite Material

This work evaluated experimentally the fatigue stress behavior of two types of composite material (SIR-epoxy resin with woven E-glass fiber as reinforcement and SIR-epoxy resin with random E-glass fiber as reinforcement) subjected to shot peening (2, 4 and 6 min) through three different times of solidification of samples (two, four and six days). The results show that, for woven reinforced composite, the great improvement in fatigue stress was obtained at both two and six days of solidification with (2, 4 and 6) min of shot peening times (SPTs) in which the percentage of the maximum enhancement was 59.38% in fatigue stress (at two days of solidification and 6 min shot peening time). For random reinforced composite the great improvement of fatigue stress was obtained at two and six days of solidification with (2, 4 and 6) min of shot peening times (SPTs) in which the percentage of the maximum enhancement was 33.78% (at two days solidification and 6 min shot peening). After four days of solidification, increasing shot peening time will decrease the fatigue stress for both types of composite materials (woven reinforcement and random reinforcement) and the maximum decreases in fatigue stresses at 6 min of shot peening was -43.06% and -28.9% for woven composite and random composite respectively. The tensile test and the fatigue test were done after full solidification of all the patterns.

Fatigue Characteristics of Materials Used in Transport Industry Applications

Abstract Designers have a major interest about fatigue properties of materials used in transport industry. Each component in transport works under alternating stress. From this point of view the fatigue properties are important for single parts lifetime resulting into safety of whole components as cars and airplanes what leads to safety on the roads or air and have influence on human life as well. Therefore this paper deals with fatigue properties of wrought Inconel alloy IN 718 and aluminum cast alloy AlSi9Cu3. Both materials were put on fatigue push – pull test, but Ni – based IN 718 alloy at frequency of loading around 20 000 kHz (High Frequency High Cycles Fatigue) and aluminum alloy AlSi9Cu3 at frequency of loading around 80 Hz (Low Frequency High Cycles Fatigue). These parameters were chosen with respect of usage such materials for production of components used in transport industry applications. Results after fatigue tests are presented as Wohler curve. For prediction of source of fracture the SEM fractography analysis of fatigue fracture surfaces was made.

On the fatigue behavior of additive manufactured lattice structures

This paper studies the effect of different factors on high cycle fatigue failure of additive manufactured lattice structure by means of numerical simulation and compare the results with experimental data in the literature. Finite element method in conjunction with failure event-based algorithm is used to simulate high cycle fatigue. The proposed algorithm is efficient and accurate for our purpose. It is shown that relative density, the fatigue strength of the bulk material and cell geometry determined the coefficient of power law function while the solid distribution and bulk material fatigue properties affect the exponent. A power law expression is proposed to predict the fatigue strength of the cellular material. The effect of different parameters on constants of the equation is discussed in detail. The results of this study render the need for performing a vast amount of experiment to determine fatigue of properties of cellular materials.

Fatigue Failure Prediction Model and Verification of Hot Extrusion Die

Fatigue fracture is one of the most common failure modes of hot extrusion dies. The fatigue properties of materials are closely related to service conditions and heat treatment processes. In this paper, the service conditions of typical hot extrusion punches were selected as the start point, loading history of the dangerous part of the die was obtained by finite element numerical simulation. The load spectrum modified and normalized through Neuber algorithm was used as the loading curve of fatigue analysis. The tensile properties of the die materials at service temperature were obtained by experiments. Based on the Manson-Coffin model, the strain-life curve of the material was obtained through the theoretical deduction. The fatigue failure prediction model was established based on strain damage. Aiming at specific working conditions of aluminum alloy extrusion parts, the fatigue life prediction and model validation of the die were carried out. The heat treatment of die was: spheroidizing annealing + 1020 ℃ oil quenching + 580 ℃× 2 h two tempering treatment. The results show that the die life predicted by the model is 1318 times, and the actual die life is 1120 times, the failure position and service life of the die are in good agreement with the predicted results. A new way was provided for optimizing the matching of heat treatment process and service condition of the die, and has guiding significance for actual production.

Effects of coating and lubrication on fretting fatigue properties of oil-well pipe material

Effects of coating and lubrication on fretting fatigue properties of oil-well pipe material

Investigation and improvement the Properties of 7075 AL/T6 Alloy using TiO2 Nanomaterials

Aluminium based metal matrix composites had drawn most attraction because of enhanced properties in structural applications for the past two decades ; therefore fatigue and tensile properties of composite materials should be studied for their structural applications .In the present research nanoparticles TiO2 were added with different weight percentage (1,3,5,7,and 9wt.%) and average particles size (10-20nm) to the 7075/T6 Al -alloy by stir casting technique. The results indicated that the tensile and fatigue properties increase with increasing the wt. % of TiO2 nanoparticle. The optical micrographs of 7075 Al- alloy with 1,3,5,7,and 9wt.%) TiO2 particles were shown uniform distribution of TiO2 and less level of porosity of microstructure compared to 7075/T6 Al-alloy and the optimum improvement in tensile and fatigue properties is occurred at 9 wt.% of TiO2.

Methodology for assessment of statistical planning effects on the S‐N curve determination using Monte Carlo simulations

AbstractOne of the most important input data in fatigue analysis is the material fatigue properties. This research aims to present a methodology for assessment of statistical planning of fatigue experiments through a MatLab algorithm developed based on Monte Carlo simulations, which enables to simulate statistically the effects of main parameters used for defining the fatigue test setting and to verify their impact on the relative percentage difference (RPD) in fatigue properties estimation comparing to a reference material. The aspects treated here have not been clearly discussed in the standards. Therefore, the proposed recommendations combined with standards procedures is a tool for test engineers, permitting a fatigue test planning with more background and precision, which can help in decisions about which is the better setup, including the sample size, number of stress levels, stress value in each level, and replication. The methodology and good practices presented in this paper were demonstrated by means of actual data from the literature.

Influence of Shot Peening Treatment on Rotating Bending High-Cycle Fatigue Properties of Additive Manufactured Maraging Steels Material

Influence of Shot Peening Treatment on Rotating Bending High-Cycle Fatigue Properties of Additive Manufactured Maraging Steels Material

A nonlinear FE analysis to model progressive fatigue damage of cross-ply laminates under pin-loaded conditions

Involving several damages and failure mechanisms result in a rather complex fatigue process of composite materials. Inhomogeneity, anisotropy and nonlinear nature of composite materials require advanced nonlinear modeling techniques of strength and fatigue. In this paper, a progressive fatigue damage model is proposed by considering the nonlinearity effects of in-plane shear stress/strain relationship. To this aim, fatigue failure criteria and material property degradations rules are derived based on material nonlinearity. The mathematical model is applied through a UMAT subroutine code developed in ABAQUS commercial software. To validate the model, life predictions are compared with the available experimental results of coupon specimen and pin-loaded carbon/epoxy cross-ply laminates. The presented finite element nonlinear progressive fatigue damage model improved the life prediction for both geometries. For coupon specimen and pin-loaded simulations, the present model reduced the average error of life predictions by 80% and 50%, respectively compared to the conventional linear models. From results of the pin-loaded model, the nonlinear assumption predicts a shorter life at high external loads due to higher stress in the fiber direction of on-axis plies as critical elements of the laminate; however, at lower external loads, both linear and nonlinear models predict similar stress state and life.

PhyBaLCHT – Influence of indentation force on the results of cyclic hardness tests and investigations of comparability to uniaxial fatigue loading

Short-time procedures for determining the fatigue properties of materials can provide significant improvements in cost efficiency and are therefore of great scientific and industrial interest (Jost et al., 2017). A promising short-time procedure is PhyBaLCHT, which is based on cyclic indentation tests and can be used to determine the cyclic hardening potential of different materials at different conditions (Kramer et al., 2014; Bambach et al., 2016). In the present research work, this procedure was used to explore the cyclic hardening potential of 42CrMo4 steel (SAE 4140) in various heat treatment states as well as of 18CrNiMo7-6 steel variants with different chemical composition and heat treatments. A special focus of the investigation was the influence of maximum indentation force on the results determined with PhyBaLCHT. As expected, a higher dependency on local effects is seen at lower indentation forces. However, consistent values of cyclic hardening potential were determined down to low indentation forces, and indent diagonals below 5 µm. This gives perspective to describe e.g. gradients in material cyclic deformation behavior with high local resolution. Furthermore, the results of cyclic indentation tests were compared to the results of uniaxial cyclic compression tests, showing transferability of the cyclic indentation tests to the cyclic deformation behavior under uniaxial cyclic loading.

The Effect of Tailored Deformation on Fatigue Strength of Austenitic 316L Stainless Steel

Fatigue failure is one of major problems of the structural components under cyclic loading; however the fatigue test is a time‐consuming and high‐cost process. Therefore, it is better to establish the relationship between the fatigue property and static mechanical properties of materials. The present studies mainly focus on the relationship between fatigue strength and tensile strength of 316L austenitic stainless steel prepared with four different technologies. The rolling results in severe plastic deformation; dislocation multiplication occurs inside the grains, and the elongated grains are parallel to the rolling direction. With the tensile strength increasing, the optimum fatigue strength reaches at an appropriate tensile strength. The fatigue strength is controlled by the tensile strength and the ability of work hardening, and based on this analysis a new method is established to estimate the fatigue strength. The competitive mechanism between fatigue crack initiation and propagation is also proposed to account for the different shapes of S‐N curves.

NUMERICAL MODELLING OF THE AIRFRAME DAMAGE GROWTH FOR THE ADHESIVE REPAIR JOINT CALCULATION

In the context of the predicted growth in air transportation, the additional attention will be paid to the organization of the competitive maintenance and repair operations for the commercial airplanes. The implementation of new technological processes for airframe repairs and the application of modern information technologies during the development of the repair procedures can be a significant advantage in the expanding market of post-production support of the commercial air fleet. Airframe adhesive repairs allow using lifting abilities of the materials more intensively, but application of the adhesive joints technology requires more complicated strength calculation procedure. It is advisable to utilize the modern finite element software packages to perform the reliable calculation. The capabilities of these software packages allow obtaining adequate computational results for adhesive repair joint parameters subjected to cyclic loads. This paper is concentrated on application of the finite element methods to simulate the crack growth in isotropic material and on methods for accelerated calculation of the mechanical response of cracked structures. Crack growth simulation is performed based on XFEM methods where the created finite element model is complemented with asymptotic imitation function of crack tip and with discontinuous jump function across the crack surfaces. Fatigue properties of the repair joint are modelled in accordance with direct cyclic approach, where a Fourier series approximation with time integration of the nonlinear material behavior is applied. After that, the result of integration at each point of the load history is used for the prediction of the material fatigue properties degradation at the next step of computation; this allows us to evaluate the material damage growth rate. Based on calculation results, a conclusion was made that the received numerical data match the full-scale test results; the time spent for calculation with the usage of accelerated computational methods was evaluated.

Laser-Based Fabrication of Carbon Nanotube–Silver Composites With Enhanced Fatigue Performance Onto a Flexible Substrate

Flexible electronic devices involve electronic circuits fabricated onto a flexible (e.g., polymer) substrate, and they have many important applications. However, during their use, they often need to go through repeated deformations (such as bending). This may generate cracks in metallic components that often exist in a flexible electronic device and could obviously affect the device durability and reliability. Carbon nanotubes (CNTs) have a potential to enhance the metal fatigue properties. However, the previous work on the fabrication of CNT–metal composites onto a flexible substrate has been limited. This paper reports the research work on a novel laser-based approach to fabricate CNT–metal composites onto a flexible substrate, where mixtures containing CNTs and metal (silver) nanoparticles (NPs) are deposited onto the substrate through a dispensing device and then laser-sintered into CNT–metal composites. Under the studied conditions and for the tested samples, it has been found that overall the addition of CNTs has significantly enhanced the bending fatigue properties of the laser-sintered material without degrading the material electrical conductivity (which has actually been slightly increased). The laser-based approach has several potential advantages, such as the local, precise, and flexible production of CNT–metal composite patterns with small or little thermal effects to the flexible substrate and other surrounding regions, and without using a mask or vacuum. Future work is certainly still needed on this novel fabrication process.

Evaluating the fatigue cracking risk of surface strengthened 50CrMnMoVNb spring steel with abnormal life time distribution

Surface strengthening is an important method which can effectively improve the fatigue property of metallic materials. In order to improve the fatigue property, for the first time, a new developed surface spinning strengthening-II (3S-II) method and the traditional shot peening (SP) treatment were applied to modify the microstructure and fatigue performance in the surface layer of 50CrMnMoVNb spring steel. It is interesting to find that the fatigue lives of the samples treated by the 3S-II method show obvious polarization characteristics (either quite higher or slightly lower than those treated by SP method) at the high stress amplitude, which does not follow the traditional life distribution rules and cannot be evaluated by the S-N curve. Moreover, the fatigue lives of the samples with the fatigue crack initiated from the surface defects are extremely lower than those of the samples whose fatigue crack initiated from the subsurface. Therefore, a fatigue risk factor, "Rf", was proposed and developed based on the competition between the applied stress and the material property to evaluate the fatigue cracking risk of the surface strengthened 50CrMnMoVNb spring steel, especially the fatigue risk of the samples influenced by the mixed factors. The calculation results show that the position where Rf max appears is exactly the position of fatigue crack initiation. As a result, "Rf" can be used to quantitatively evaluate the fatigue risk of metallic material under the influence of a variety of factors, including surface strengthening, surface roughness and residual compressive stress and so on.

Effect of uncertainty sources on the reliability level of wind turbine rotor blades

AbstractWind turbine rotor blades are large composite structures performing most of their design life under random cycle loading patterns. Concurrently, material properties of the constituent plies exhibit inherent variability. In order to ensure a safe and cost‐effective design, uncertainty related to the basic variables (material properties, loads etc.) should be quantified and taken into account in the design calculations. Recently, the blade design standard DNVGL‐ST‐0376 was released, showing the trend of using dedicated probabilistic analysis for wind turbine blade design. A critical evaluation of the new edition of the standard is performed herein, particularly in terms of the ability of the suggested safety factors to satisfy the target failure probability level of 1E‐04. To this end, probabilistic analysis methodology is employed, starting with the measurement uncertainty for the static and fatigue properties of the composite material and going all the way up to the blade failure probability on a layer by layer basis. The application is performed on the INNWIND.EU reference 10MW rotor blade of 90‐m length. Furthermore, the current reliability level of the specific blade design, following the new standard DNVGL‐ST‐0376, is estimated considering the various failure modes, ie, fibre failure (short term and fatigue strength), buckling, and inter fibre failure of the composite laminates, while taking into account sources of variability that contribute to the physical, statistical, measurement, and model uncertainty. Results indicate that while for the static (extreme) analysis deterministic results are conservative, the opposite is observed for fatigue analysis.

Defect size map for nodular cast iron components with ellipsoidal surface defects based on the defect stress gradient approach

The impact of surface defects on the fatigue properties of cast iron material cannot be neglected in the fatigue design process. Allowable defect size maps are a practical tool for the quality control of surface defects on castings. These results present a compliance between the detrimental effect of surface inhomogeneities and the primary requirement of structural integrity during service life. The Defect Stress Gradient approach from Vincent et al. (2014) has been further improved by a general ellipsoidal geometry model for surface defects, and has been utilized for the fatigue assessment of defective nodular cast iron. After the study of defect size, shape and orientation effects calculations are compared with experimental results for high-strength ferritic nodular cast iron and 1045 steel. Two methods are proposed for an allowable defect size map based surface defect assessment using ellipsoidal description of the defect. The ellipsoidal description of the defect size, shape and orientation offers a more precise representation of real defects leading to more accurate results than the established hemispherical notch or surface crack methods.