Fatigue Test Method Research Articles

Optimized method for multi-axial fatigue testing of wind turbine blades

An optimized method for testing wind turbine blades under fatigue is suggested. With this method, material-based damage targets along the blade are reached by applying an optimal combination of different uni- and multi-axial test blocks. The combination of test blocks is found using continuous linear optimization. Aeroelastic simulations are carried out to estimate both target and test strain-based damage in the blade. By applying the proposed method to a commercial wind turbine blade, the presented analysis illustrates that improved fatigue tests compared to current standard fatigue tests can be obtained in terms of both accuracy and total test time.

Research on Bench Fatigue test method of frame under torsion condition

In order to predict the fatigue life of frame, a new bench test method of the frame torsion fatigue is proposed, which can approximately reflect the results of enhanced road test. The frame finite element model was established and the simulation was carried out to determine the dangerous position of fatigue life failure. The load spectrum of the fatigue dangerous position was collected, and the fatigue damage value was analyzed by the rain-flow counting method and Miner criterion. The equivalent conversion relationship of the fatigue life between bench test and road test was established. The mean error between theoretical calculation result and bench test result is 5.2 %; The mean error between theoretical calculation result and road test result is 3.85 %. The results showed that the bench test method of frame torsion fatigue can improve the precision and reliability of the frame fatigue life prediction.

A Study of Fatigue Crack Growth Rate in Steels in Relation to Crack-Tip Plastic Deformation and Fracture. Part 2. Parametric Relation between Fatigue Crack Growth and Plastic Strains

The first part of this study presented low-cycle fatigue and cyclic fracture toughness test methods for 10GN2MFA steel at 20 and 270°C, experimental results to construct kinetic fatigue fracture diagrams and to determine low-cycle plastic strain and fracture characteristics. Here, those results are estimated as to the application of cyclic plasticity to describe the fatigue crack growth rate. The cyclic strain-hardening coefficient and the Paris–Erdogan equation exponent for ferrite-pearlite steels are shown, to be closely related as well as the intersection point of the diagram in the range of high crack growth rates was defined. The parameters of the above relation and coordinates of the intersection point were determined for the steels of this class. In the latter case, the optimization methods were used to find the minimum sum of squares of residual functions. Based on the correlation between the cyclic strain-hardening coefficient and Paris–Erdogan equation exponent, the conclusion was drawn of the lower boundary value of this characteristic predicted for an ideal elastoplastic material (zero cyclic strain-hardening coefficient), to be equal to 1.0. As also follows, other classes of the materials (and other cycle asymmetries) can exhibit similar relations in the form of rays coming from the point (0; 1.0) at a corresponding experimental slope to the coordinate axes. From the common intersection point of the diagram (Gurney point) and their slopes to the axes for ferrite-pearlite steels, the procedure was advanced to construct the linear section of the diagram based on the results of low-cycle fatigue tests with plotting the stress amplitude vs. plastic strain amplitude curve. The procedure was approved on 10GN2MFA steel at 20 and 270°C and SAE-1020 and API5L X60 steels taken from the literature. In view of data scattering for cyclic fracture toughness test results, the estimation of the linear diagram sections is quite adequate, and the procedure of their construction is appropriate and can be extended to other classes of the materials and stress ratios.

Interface characterization of Cu[sbnd]Cu ball bonds by a fast shear fatigue method

A highly accelerated shear fatigue testing method is presented to test the long-term reliability and reveal the bonded interface of thermosonic CuCu ball bonds. The method is an adaptation to a new industrial fatigue tester (BAMFIT) and can be conducted without an intricate specimen preparation. This method induces mechanical cyclic shear stresses to the Cu nailhead in order to initiate fatigue fracture until lift-off, revealing the actual bonded interface. This study compares the fatigue resistance of Cu wire bonded to coarse and fine grained Cu and Al metallization. The fatigue experiments are accompanied by nano indentation tests, shear tests and finite element analysis. The fatigue results showed the best performance for Cu bonds on coarse grained Cu pads (metallization), followed by those bonded on fine grained Cu while the CuAl nailheads failed at least a decade earlier than CuCu bonds. Annealing the specimens prior to testing resulted in slight increases in the number of loading cycles to failure (Nf) for Cu bonds as well as for CuAl bonds, while the scattering in Nf for Cu bonds increased. Nevertheless the calculated endurance limit of the fatigue data decreases with increasing annealing stages, due to a change in the fracture probability curve. With the ability to compare the fatigue behaviour of the bonded interface within minutes, this method is most suitable for rapid qualification at an early stage of development.

Fatigue resistance characterization of frictions stir welds between complex aluminum extrusions: An experimental and finite element study

This paper presents a detailed experimental and computational investigation into fatigue behaviors in friction stir welds at both joint and component level for welded assemblies of complex 6005A-T6 aluminum extrusion profiles. A novel fatigue test method was developed for characterizing FSW joint fatigue resistance in a structural context. The fatigue test data obtained in this study were then generalized by using a traction-based structural stress method. The results show that the fatigue test data and their S-N curve representation can be used as a basis for supporting fatigue evaluation of friction stir welds joining complex aluminum extrusions.

Development of fatigue damage model of asphalt mixtures based on small-scale accelerated pavement test

As the primary surface type for high-grade Chinese highways, the long-term performance of asphalt pavement can affect significantly transportation efficiency. It has been confirmed that fatigue cracking is one of the major failure modes for asphalt pavement, which can cause a great reduction of asphalt pavement durability. Currently, the fatigue properties of asphalt mixtures are evaluated mainly based on traditional laboratory fatigue tests, such as bending fatigue tests and indirect tensile fatigue tests. However, none of these fatigue test methods can realistically evaluate the fatigue performance of asphalt pavement under the repeated wheel load. To resolve this issue, the model mobile load simulator (MMLS3), which is a small-scale accelerated pavement test device, was utilized to evaluate the fatigue life of six kinds of asphalt mixtures. The fatigue damage variable was defined as stiffness reduction. Based on the small-scale accelerated pavement test, a stiffness reduction model for asphalt mixtures was determined. A stiffness reduction law for asphalt mixtures during the fatigue process was proposed. The stiffness evolution process could be divided into three phases, which are the adaptation phase, the quasi-stationary phase, and the failure phase. A maximum value of the rate of stiffness reduction from the quasi-stationary phase into the failure phase was proposed as the failure threshold. Besides the fatigue life obtained from the failure criteria had a good agreement with the test results. The results from this research can be used as a theoretical reference for evaluating the fatigue life of asphalt mixtures and improving the durability of asphalt pavement.

Evaluation of fatigue properties of reduced activation ferritic/martensitic steel, F82H for development of design criteria

Reduced activation ferritic/martensitic (RAFM) steels are promising candidate for structural material of tritium breeding blanket in a fusion reactor. Database accumulation and definition of design criteria for RAFM have been intensively studied together with the progress of blanket design activities. As a part of database accumulation for fusion blanket, a RAFM steel, F82H was fatigue-tested at 573 and 673 K in the air. Axial strain-controlled fatigue tests were carried out with a cylindrical specimen with 8 mm of diameter with -1 of strain ratio condition in accordance with Japanese Industrial Standard, JIS Z 2279, “Method of high-temperature low cycle fatigue testing for metallic materials.” For high cycle tests, the maximum test cycles exceeded 106 cycles. Fatigue lifetime of F82H at temperatures ranging from room temperature to 673 K fell into the factor of 2 of the empirical fitting curve for 673 K. It was studied using experimental results that fatigue-related design limit based on RCC-MRx, such as fatigue design curves, half-life cyclic curves, and related coefficients.

Comparison of cyclic fatigue resistance of Rotate instrument with reciprocating and continuous rotary nickel-titanium instruments at body temperature in relation to their transformation temperatures.

The aim of this study was to compare the cyclic fatigue resistance at body temperature and phase transformation behaviors of novel Rotate instrument (25.06) with rotating Mtwo (25.06) and reciprocating Reciproc Blue (25.08) and Reciproc (25.08) instruments. The Rotate, Reciproc Blue, Reciproc, and Mtwo instruments free of visible deformations were collected and tested in a static cyclic fatigue test method, which has a ceramic block containing an artificial canal with 60° angle of curvature and a 5-mm radius of curvature at 37 °C (n = 16). All instruments were operated until fracture occurred, and both time to fracture (TF) and the lengths of the fractured fragments were recorded. TF data was analyzed with one-way ANOVA followed by post hoc Tukey tests and Weibull analysis, and fractured fragment length data were subjected to one-way ANOVA and post hoc Tukey tests (P < 0.05). Two unused instruments from each brand were also subjected to differential scanning calorimetry (DSC) analysis to determine their phase transformation temperatures. The Reciproc Blue instruments showed significantly higher TF values and reliability than the other groups (P < 0.05). Rotate instruments exhibited greater cyclic fatigue resistance than the Reciproc and Mtwo instruments (P < 0.05). No significant difference was detected among the fractured fragment lengths (P > 0.05). The lowest austenite finish temperature was exhibited by the Mtwo, which presented a single transformation peak, followed by the Rotate, Reciproc Blue, and Reciproc instruments which all presented two peaks during transformation. Cyclic fatigue resistance of instruments manufactured from thermally treated Blue wire instruments was superior to those of the Mtwo and Reciproc, whereas reciprocating the Blue wire showed the highest resistance. The present study compared the cyclic fatigue resistance of the novel Rotate instrument with similar instruments manufactured from conventional nickel-titanium, m-wire, and Blue wire at body temperature and reported that Blue-treated instruments exhibited superior cyclic fatigue resistance.

Review of Multiaxial Testing for Very High Cycle Fatigue: From ‘Conventional’ to Ultrasonic Machines

Fatigue is one of the main causes for in service failure of mechanical components and structures. With the development of new materials, such as high strength aluminium or titanium alloys with different microstructures from steels, materials no longer have a fatigue limit in the classical sense, where it was accepted that they would have ‘infinite life’ from 10 million (107) cycles. The emergence of new materials used in critical mechanical parts, including parts obtained from metal additive manufacturing (AM), the need for weight reduction and the ambition to travel greater distances in shorter periods of time, have brought many challenges to design engineers, since they demand predictability of material properties and that they are readily available. Most fatigue testing today still uses uniaxial loads. However, it is generally recognised that multiaxial stresses occur in many full-scale structures, being rare the occurrence of pure uniaxial stress states. By combining both Ultrasonic Fatigue Testing with multiaxial testing through Single-Input-Multiple-Output Modal Analysis, the high costs of both equipment and time to conduct experiments have seen a massive improvement. It is presently possible to test materials under multiaxial loading conditions and for a very high number of cycles in a fraction of the time compared to non-ultrasonic fatigue testing methods (days compared to months or years). This work presents the current status of ultrasonic fatigue testing machines working at a frequency of 20 kHz to date, with emphasis on multiaxial fatigue and very high cycle fatigue. Special attention will be put into the performance of multiaxial fatigue tests of classical cylindrical specimens under tension/torsion and flat cruciform specimens under in-plane bi-axial testing using low cost piezoelectric transducers. Together with the description of the testing machines and associated instrumentation, some experimental results of fatigue tests are presented in order to demonstrate how ultrasonic fatigue testing can be used to determine the behaviour of a steel alloy from a railway wheel at very high cycle fatigue regime when subjected to multiaxial tension/torsion loadings.

Loads Simplification on Multi Input Axle Systems

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;The time domain is currently the most widely chosen option in fatigue testing to fully represent random events occurring in multiple simultaneous input channels. In vehicles for example, time domain tests can represent the same conditions of the road, by applying the same loads at the hard points of the vehicle along a time history. The main drawback of this methodology is the extensive testing duration and hardware cost. Time domain based fatigue tests are composed of a complex hardware, which requires servo motors to work, in order to induce the specific amount of load at a specific time window. These tests are time consuming, since they require the same length duration of the event they are reproducing, times the required repetitions. The frequency domain method for fatigue testing, on the other hand, requires simpler hardware, since there are no need for servomotors and the test length is reduced, since there is no need to run the full event times the required repetitions. The drawback in this case is the ability to represent random events with multiple simultaneous input channels. For this reason, frequency domain tests are mainly applied for simple round-robin tests, unable to represent random events like a road condition. In this work, we will present a new methodology that uses the fatigue result as input, reversing it in order to find the loads that would be required to originate it in frequency domain. This new methodology can help future developments in fatigue test, replacing time domain tests without losing accuracy and the ability to represent random events occurring in multiple simultaneous input channels.&lt;/div&gt;&lt;/div&gt;

Low cycle fatigue testing using miniature specimens

This study discussed a low cycle fatigue testing method using miniature specimens of SUS304 stainless steel and S35C carbon steel. A stable low cycle fatigue testing method was developed for miniature specimens with a 1 mm diameter that gives similar low cycle fatigue lives of bulk specimens with a 6.5 mm diameter. The testing method assessed the effects of surface roughness and residual stress. The results showed that low cycle fatigue damage could be evaluated using miniature specimens taken from the cracked parts of bulk specimens.

Ultrasonic fatigue testing under multiaxial loading on a railway steel

Ultrasonic fatigue testing is a relative recent fatigue study methodology that applies resonant principles for the induction of stress cycles in a specific designed material specimen. Such experimental method can apply fatigue damage at high frequencies, most commonly at 20 kHz. It was created with the main purpose of studying material fatigue life in the Very High Cycle Fatigue regime between 10E07 and 10E09 cycles with a higher performance of time and energy wise in comparison to conventional servo-hydraulic machines.In this study an ultrasonic fatigue testing machine was used in order carry out multiaxial tension/torsion fatigue tests at a frequency of 20 kHz. The main objective was to reach a reliable multiaxial fatigue testing method, by modifying only the specimen, with the ability to choose the shear-axial stress ratio.The improved design of the testing method was focused in innovative design specimen by conducting both numerical and experimental analysis. Thermographic imaging, laser displacement measurements, and the application of rosette strain gauges to the main stress region of the specimen were carried out in order to validate the new improved design concepts. These strain and displacement results were compared with the ones obtained by finite element and a good agreement was achieved.A first series of fatigue tests were carried out intension/torsion multiaxial fatigue and the results are discussed in order to understand the feasibility of multiaxial fatigue tests at ultrasonic frequencies.

Low-Cycle Fatigue Behavior of Thin-Sheet Extruded Aluminum Alloy

In this work, we investigate a novel testing method for fatigue testing of a thin sheet under fully reversed conditions. Specifically, the fatigue behavior of thin-plate AA6082-T6 was characterized by laminating multiple thin gage specimens together to form a thicker specimen to prevent buckling under low-cycle fatigue testing. In this unique technique, ASTM E606 fatigue specimens were bonded together with a structural adhesive in double and triple laminates, and fatigue behavior was compared against monolithic control specimens. To quantify the fatigue behavior of the laminated AA6082, strain-controlled experiments were conducted, where the fatigue life experimental results exhibited comparable fatigue performance to the published literature. Postmortem analysis of the laminated AA6082 revealed a similar fatigue nucleation and crack growth damage mechanisms compared to the monolithic fatigue specimens. Lastly, a microstructure-sensitive fatigue life model was utilized to elucidate structure–property fatigue mechanism relations of the monolithic, double-, and triple-laminate specimens. The fatigue behavior of laminated specimens exhibits good correlation to wrought AA6082-T6 mechanical properties and thus suggests that laminating sheets together can be used to quantify fully reversed fatigue behavior of thin sheets that would otherwise buckle under compression loading.

Expectation method for fatigue limit of used rail on railway by surface roughness and effect of difference of various fatigue test methods

Expectation method for fatigue limit of used rail on railway by surface roughness and effect of difference of various fatigue test methods

Fatigue of Tungsten Fiber/Copper Matrix Composite—An Interlaboratory Study

Abstract Seven laboratories participated in an interlaboratory study to assess the applicability of ASTM E606, Test Method for Strain-Controlled Fatigue Testing, to strain-controlled fatigue of a tungsten fiber/copper matrix composite (Battelle Columbus, University of Iowa, IITRI, MCL, MarTest, Rockwell International Science Center and University of Twente). Because of the material and specimen fabrication methods, the number of fibers in the 9, 25, and 36 % fiber volume fraction specimens is approximately the same and the strain-life data are nearly identical for each of the volume fractions. Although the specimen aspect ratio is within the nominal range, the specimen diameter is less than the nominal value specified in ASTM E606. Laboratories reporting data noted that a small specimen diameter and a large gage section aspect ratio made specimen alignment difficult. Thus, specimen buckling was problematic at high strain ranges. The study data are reported and analyzed with nonparametric and semiparametric statistical methods to assess the effect of study covariates on fatigue life. The median fatigue life, median absolute deviation from the median, and interquartile range are reported as measures of central tendency and variability. ASTM E606 may be used as a guide to evaluate the fatigue response of this type of composite material if the length-to-diameter aspect ratio, specimen alignment in the fatigue machine, and specimen surface finish are closely monitored to ensure valid data.

Proposal of an ultrasonic fatigue test method and evaluation of fatigue properties for L-shaped quasi-isotropic CFRP laminates

Proposal of an ultrasonic fatigue test method and evaluation of fatigue properties for L-shaped quasi-isotropic CFRP laminates

Study on Fatigue Limit Test of TCS Stainless Steel

Material fatigue limit plays a vital role in the fatigue life of railway vehicle parts. According to the fatigue test method, the fatigue performance of TCS stainless steel used in railway rolling stock was studied in this paper. The corresponding fatigue limit calculation methods of lifting method and group method were given, and the P-S-N curve of TCS stainless steel under test conditions and fatigue limit under different survival rates were obtained. The results showed that the fatigue limit of TCS stainless steel was 176.43 MPa under 50% survival rate, 163.21 MPa under 90% survival rate, and 152.44 MPa under 99% survival rate. The results of this paper provide basic data for the application of TCS stainless steel in railway rolling stock.

Basic study on a new fatigue test method for transmission chains

Basic study on a new fatigue test method for transmission chains

Influence of Rest Period on the Fatigue Response of Bituminous Mixture at Low Temperature

Laboratory fatigue characterization of bituminous mixtures is carried out typically by conducting a beam bending test at a given frequency and temperature for various strain/stress levels. In the current fatigue test methods, the material is tested at 20°C with continuous loading, and the fatigue life is estimated based on the stiffness modulus and energy dissipation. Very little data exist on the influence of low temperature (0°C), and tests with a rest period. In this study, the fatigue life of the bituminous mixture is estimated at 20 and 0°C, and the influence of the rest period is quantified. For this purpose, a typical bituminous mixture used in Indian highways was fabricated. Experiments were conducted at 0 and 20°C with and without a rest period in strain-controlled mode (600 and 800 microstrains) in a four-point beam bending test setup. For tests with a rest period, a 0.9 s rest period was provided after 0.1 s loading. The evolution of stiffness modulus as per AASHTO T321 [1] and normalized modulus by ASTM D7460 [2] was used in fatigue life estimation. Also, the evolution of energy dissipation during testing was analyzed to characterize the response of material (elastic/viscoelastic) and the beneficial effect of the rest period, if any. The influence of the rest period was more pronounced when tested at 20°C in comparison to testing at 0°C.

Fatigue behavior of RC beams strengthened with CFRP laminate under hot-wet environments and vehicle random loads coupling

Fatigue behavior of main load-bearing reinforced concrete (RC) members of highway bridges is heavily influenced by service environmental attacks and vehicle random loads. To investigate the fatigue behavior of RC beams strengthened with CFRP on highway bridges served under hot-wet environments and vehicle random loads, a novel environmental fatigue test method was proposed in the current research. Three-point bending fatigue tests on RC beams strengthened by carbon fiber laminate (CFL) with five combinations of hot-wet environments (10 °C & 50%R∙H, 23 °C & 78%R∙H, 50 °C & 50%R∙H, 50 °C & 78%R∙H, 50 °C & 95%R∙H) and three sets of random loading levels (ΔPmean = 18.3 kN, 19.9 kN, 21.6 kN) were carried out. The results showed that coupling action of hot-wet environment and vehicle random load has a significant effect on the fatigue failure mode (including tensile rebar fracture and CFL debonding), fatigue stiffness and fatigue lives of the strengthened beams. Fatigue lives of the strengthened beams under vehicle random loads was lower than constant amplitude loads and ladder amplitude loads. Environmental random fatigue lives decreased with the increase of relative humidity and temperature. To facilitate and accurate environmental random fatigue life prediction, environmental random fatigue equations which were able to consider the influence of coupling effect of hot-wet environments and the vehicle random loads on fatigue lives and fatigue limits of the strengthened beams were established and verified against the test data.