Previous Fatigue Tests Research Articles

Numerical analysis on fatigue behavior of ultrahigh-performance concrete-Orthotropic steel composite bridge deck

Ultrahigh-performance concrete-orthotropic steel composite bridge deck is composed of the orthotropic steel deck and a thin ultrahigh-performance concrete (UHPC) overlayer. In the previous fatigue tests, two typical fatigue failure modes were found and identified. As a supplementary test after fatigue tests, air penetration method is capable of providing a reference to the quantitative and non-destructive damage detection of fatigue damage of UHPC. To further the previous study, a detailed numerical investigation is accomplished through complimentary finite element (FE) analysis. Compared with the solid element model, the refined shell-solid element model can better reflect the mechanical behavior. It is illustrated that the vertical stress can be adopted in assessing the fatigue strength of rib-to-diaphragm welded connection in the field test by means of nominal stress method. The combination of various factors would lead to fatigue shear failure of the short headed-studs. The fatigue strength of rib-to-diaphragm welded connection predicted by the hot spot stress method and the consistent nominal stress (CNS) method can basically meet the requirements of FAT90. The consistent nominal stress method can be used as the optimization method of nominal stress of fatigue detail. It is demonstrated that the fatigue life of UHPC can be estimated by S-N curves of ordinary concrete conservatively. The allowable equivalent maximum stress level can be taken as 0.55 for two million cycles of fatigue loading, and 0.52 for five million cycles of fatigue loading.

The influence of quenching on fatigue life of Ti6Al4V alloy

Titanium Ti6Al4V alloy falls into the α+β category alloy system. It is widely used due to its unique mechanical and physical properties which can be modified by applied heat-treatment. The α-phase is considered to be the main phase influencing mechanical properties of an alloy such as ultimate tensile strength or ductility. However, it has also influence on the fatigue life where the form and presence of α-phase in prior β grains may increase or decrease fatigue life. The length and width of α-lamellae influence on fatigue life is well-known. A lot of authors have done their experiments on alloys with Widmanstätten or acicular α-phase structures. Our goal was to obtain an α’-martensitic structure in prior p grains and investigate its influence on fatigue life. To fulfil this goal the heat-treatment consisted of heating near above β-transus temperature 1050°C for a dwell time of 3 hours followed by water quenching was applied. After heat-treatment, the set of specimens with dimensions 10 mm x 9 mm x 55 mm were subjected to three-point bending fatigue test with the parameter of cycles asymmetry R < 1 and test frequency f = 69 Hz. The S-N curve of fatigue life was plotted after the fatigue test and SEM fractography analysis of fractured surfaces was done as well. Our results were compared to previous fatigue test done on alloy with α-lamellae structure.

Fatigue experiment of sectional integrated model of a suspension bridge

Previous fatigue tests have placed emphasis on single components such as the anchorage zone, orthotropic steel deck or hanger of suspension bridges, and the test results were thus influenced by many boundary conditions. However, the stresses of such components are complex and boundary conditions have a marked impact on fatigue test results. To evaluate the safety and durability of key structural details and verify the design rationality, fatigue tests on a 1:4 scale integrated model were carried out; the model included the main cable, anchorage zone, hangers and box girders. The experiment results showed that stress redistribution in the integrated model after fatigue loading cycles was not obvious, the principal stresses of static load tests during the fatigue experiment were a little different and the relationship between displacement and static load was approximately linear. In each static load test, displacements and stresses in the process of loading and unloading showed good symmetry and recoverability, indicating that the integrated model was in the elastic stage. Fatigue cracks were not found in key structural details under fatigue loading, so structural fatigue performance may meet the design requirements. The integrated model fatigue test can more truly reflect the actual fatigue performance of a cable–anchorage–hanger–girder structure and can provide some guidance on actual projects.

Reaction kinetics approach in relation to the fatigue life of wood

To evaluate the mechanical durability of wood, it is necessary to evaluate the phenomenon of fatigue progress with respect to the cumulative load process over time. Fatigue life estimation by reaction kinetics along with energetics in fatigue strength analysis is proposed based on previous studies. In this regard, based on the reaction kinetics proposed by Eyring, Liu and co-workers derived the reaction rate model for sinusoidal load, whereas this study derived new reaction rate models for square wave. In order to validate the derived model, the fatigue life was estimated using the previous fatigue test results of wood. The results of the fatigue life estimation calculations using the derived reaction rate model confirmed that the estimated value of fatigue life generally matched well with the experimental values, though room for further examination is left in the interpretation of how the parameter included in the model relates to the wood species’ special quality, load conditions and so on. Thus, the possibility of a reaction kinetics approach to examine the fatigue life of wood was demonstrated.

09.09: Experimental fatigue analysis of high strength steel structures

ABSTRACTThere are contradictional information in the previous studies regarding the relationship between the fatigue strength and the yield strength in case of steel structures. Several previous test result show that the fatigue strength of as‐welded specimens do not depend on the yield strength of the base material. However, several studies show that the fatigue detail class of HSS structure can be higher than for structures made form NSS material for the same structural detail. Collecting the previous fatigue test results of cruciform and flange gusset structural details the effect of the yield strength on the fatigue behaviour is studied. Additional laboratory test program with 32 test specimens is performed to investigate the fatigue behaviour of structural details typically used in bridges produced from HSS and NSS material. For cruciform welded joints the test results show clear correlation between the yield strength and the fatigue life time. For flange gusset joints this relationship cannot be observed. In addition, post weld treatment of the flange gusset plate joint is studied. Using the results of the fatigue tests the fatigue lifetime increase applying the grinding type post‐weld treatment is evaluated.

Fatigue behaviour of CHS tubular bracings in steel bridges

The structural solution for cross girder bracings or box girder diaphragms in steel bridges is often made with tubular elements, specially efficient if compression is required for structural behaviour. The connection between the tubular elements and the girder plates is usually made with a gusset welded on a slit in the tube. The weld between the gusset and the tube at the end of the slit is a critical fatigue spot. This paper re-analyses the existing fatigue detailing recommendations and presents the results of fatigue tests carried out on CHS tubes with four different types of detail in the high cycle regime. The results were analysed with a local notch stress approach and compared with previous fatigue tests from literature. Recommendations for fatigue classification and detailing are given.

A Rapid Fatigue Test Method on Micro Structures for High-Cycle Fatigue

Here, a rapid fatigue test method for micro structure is proposed, where the test sample is excited at its resonant frequency by an external actuator. Due to the scaling effect, a micro cantilever beam has high resonant frequency, so the testing time can be greatly reduced. In addition, no complicated built-in micro actuator is needed; therefore, it is easy to fabricate the test sample. Single-crystal silicon (SCS) beams are fabricated to demonstrate the proposed method here with two types of beams. A notch is designed near the fixed end to have stress concentration effect. The input voltage of the piezoelectric patch is adjusted to excite the cantilever beams at its resonant frequency to have different amplitudes to find the corresponding fatigue life, where a laser Doppler vibrometer is used to monitor displacements of the cantilever beam to control the stress amplitude. Then, the stress–life (S/N) curve of the silicon beam can be obtained. It is found that the fatigue limit of the SCS beam is about 1.33 GPa, and it takes only about 5.2 h to test $\mbox{1.35}\times \mbox{10}^{9}$ cycles at a resonant frequency of 72 kHz. Comparing with previous fatigue test methods with an external probe, testing $\mbox{10}^{9}$ cycles at a frequency of 20 Hz will need 1.58 years, which indicates that the proposed rapid fatigue test method is particularly suitable for high-cycle fatigue test of micro structure.

VHCF Strength of Helical Compression Springs - Influence of Heat Treatment Temperature before Shot Peening

Previous fatigue tests show that the heat treatment temperature has a significant influence on high cycle fatigue behaviour of helical compression springs. In order to investigate the effect of the heat treatment temperature on the fracture behaviour and the cyclic life, fatigue tests in the very high cycle regime (VHCF) were conducted.The tested springs were manufactured from oil hardened and tempered SiCr-alloyed valve spring steel wire with a diameter of d = 1.6 mm. After winding and grinding of the spring endings, the springs were heat treated at either 360°C or 400°C for 30 minutes. In order to generate compressive residual stresses in the surface area, the springs were shot peened. After shot peening, the springs were again annealed at 240°C for 30 minutes.Fatigue tests were conducted at 40 Hz using a special spring fatigue device. Up to 900 springs were tested simultaneously at various stress levels to 5∙108or 109cycles. Fractured springs were investigated by means of a stereomicroscope as well as a scanning electron microscope to analyse the fracture behaviour and failure mechanisms. The vast majority of the springs show crack initiation at the surface at the inner side of the coil. Less frequently, crack initiation occurs at subsurface locations. Our results show that heat treatment at a temperature of 360°C leads to four times more subsurface cracks than at a temperature of 400°C and reduces the overall fatigue life time.

Evaluation of anti-reflective cracking measures by laboratory test

A laboratory simulation of load-induced reflective cracking was carried out using Hamburg wheel tracking tester (HWTT). The simulation, compared with some previous fatigue tests, is more reasonable and applicable because, instead of static load, the cyclic dynamic load is applied to the specimens and the test is relatively time and cost saving. The purpose of this study was to evaluate the effectiveness of various stress-absorbing interlayers to retard the development of reflective cracking, including styrene-butadiene-styrene (SBS)-modified asphalt sand concrete interlayer, asphalt-rubber sand concrete interlayer, fibreglass-polyester paving mat interlayer and stress-absorbing membrane interlayer (SAMI). Specimens without any anti-reflective cracking measure were also included to serve as a control. This paper first describes material properties, aggregate gradations and the simulation apparatus. Then, it assesses the effectiveness of different measures to prevent reflective cracking based on laboratory test results. It reveals that asphalt-rubber sand concrete interlayer performed best and fibreglass-polyester paving mat interlayer ranked next, whereas both SBS-modified asphalt sand concrete interlayer and SAMI showed similar and less sound performances compared with the former two under laboratory test environments. However, SAMI may witness an improved field performance due to the limitation of laboratory test set-up and any of the four measures could prolong the fatigue life of the specimens substantially. A finite element model simulation was followed to explain the anti-reflective cracking mechanism and support the HWTT results.

Fatigue strength improvement of welded joints by blast cleaning for subsequent painting

In the fabrication of steel bridges, prior to painting, blast cleaning is performed to clean the surfaces and to increase the adhesive properties of the surfaces for the subsequent painting. In addition to these objectives, blast cleaning can improve the fatigue strength of welded joints, as a result of the impact of forcibly propelled abrasive materials on the welded joints. A series of fatigue tests were carried out on the five different types of welded joints: one-side out-of-plane gusset fillet welded joints, both-side out-of-plane gusset fillet welded joints, non-load-carrying rib fillet welded cruciform joints, butt welded joints, and a large-scale model beam with out-of-plane gusset welded joints, and under the three different types of load conditions: uniaxial tension, out-of-plane bending, or in-plane bending stress cycles. Drawing on previous fatigue test results that include unpublished data, this paper presents the beneficial effects of blast cleaning for the subsequent painting applications on the fatigue strength improvement of welded joints and also presents a simple quality control method for the blast cleaning process that improves the fatigue strength.

Fatigue Strength of Steel Rollers and Gears Treated by Cavitation Peening with Short Processing Time (A Case of Processing Time of 1 min and 5 min)

In this study, steel rollers and gears were treated by the cavitation peening with processing times of 1 min and 5 min, and they were fatigue-tested using a roller testing machine and a gear testing machine. The surface hardness and the compressive residual stress of the rollers and gears were increased by the cavitation peening, while, the surface roughness of the cavitation-peened rollers and gears was almost the same as that of the non-peened ones. As a result of the fatigue tests, the fatigue strength of the test specimens were improved by the increase in surface hardness due to the cavitation peening, and those without the increase in surface hardness were not increased so much. The fatigue strength of the cavitation-peened test specimens was similar to that of the shot-peened ones obtained by the previous fatigue tests. This study revealed that the cavitation peening is expected to put to practical use in the improvement in fatigue strength of steel gears.

PREDICTION OF CRANKSHAFT FATIGUE LIMIT LOAD BY CRACK-MODELING TECHNIQUE

In this paper, combining the previous crankshaft fatigue test data with Crack-Modeling Technique, the threshold stress intensity range, ΔKth of crankshaft can be derived. The calculated threshold, ΔKth takes the effect of material properties and processing technology into account. Then, using the threshold, ΔKth, we can predict the fatigue limit load of the different types of crankshafts with the same material properties and processing technology by Crack-Modeling Technique. This study shows that the standard crack may be a good equivalent to the crankshaft stress concentration and the prediction of the crankshaft fatigue limit load is accurate.

Validation of BS7910:2005 failure assessment diagrams for cracked square hollow section T-, Y- and K-joints

This paper describes the usage of finite element (FE) analyses results to validate the standard BS7910 assessment procedure for the safe design of cracked square hollow section (SHS) T-, Y- and K-joints. In the study, the actual 3D surface cracks obtained from previous fatigue tests have been included in the FE models. An automatic mesh generation program is then developed and used to produce the failure assessment diagram (FAD) through the J-integral method. The ultimate strength of uncracked SHS joints with reduced load bearing areas have been referenced to derive the plastic collapse loads of cracked SHS joints for the development of FAD. These loads have been validated against the previous experimental results. In comparison with the existing standard BS7910 Level 2A/3A FAD curve and the proposed assessment procedure for circular hollow section joints, it is found that a plastic collapse load with a penalty factor of 1.05 will be sufficient for the safe assessment of cracked SHS T, Y, and K-joints under brace end axial loading.

Bonded aircraft repairs under variable amplitude fatigue loading and at low temperatures

Bonded repairs can replace mechanically fastened repairs for aircraft structures. Compared to mechanical fastening, adhesive bonding provides a more uniform and efficient load transfer into the patch, and can reduce the risk of high stress concentrations caused by additional fastener holes necessary for riveted repairs. Previous fatigue tests on bonded Glare (glass‐reinforced aluminium laminate) repairs were performed at room temperature and under constant amplitude fatigue loading. However, the realistic operating temperature of −40 °C may degrade the material and will cause unfavourable thermal stresses. Bonded repair specimens were tested at −40 °C and other specimens were tested at room temperature after subjecting them to temperature cycles. Also, tests were performed with a realistic C‐5A Galaxy fuselage fatigue spectrum at room temperature. The behaviour of Glare repair patches was compared with boron/epoxy ones with equal extensional stiffness. The thermal cycles before fatigue cycling did not degrade the repair. A constant temperature of −40 °C during the mechanical fatigue load had a favourable effect on the fatigue crack growth rate. Glare repair patches showed lower crack growth rates than boron/epoxy repairs. Finite element analyses revealed that the higher crack growth rates for boron/epoxy repairs are caused by the higher thermal stresses induced by the curing of the adhesive. The fatigue crack growth rate under spectrum loading could be accurately predicted with stress intensity factors calculated by finite element modelling and cycle‐by‐cycle integration that neglected interaction effects of the different stress amplitudes, which is possible because stress intensities at the crack tip under the repair patch remain small. For an accurate prediction it was necessary to use an effective stress intensity factor that is a function of the stress ratio at the crack tip Rcrack tip including the thermal stress under the bonded patch.

Influence of a voluntary fatigue test on the contralateral homologous muscle in humans?

Influences of a submaximal endurance test in the right first dorsal interosseus on force and fatigue-related parameters of activating the contralateral muscle were studied. The test consisted of a 30% maximum voluntary contraction (MVC), regularly interrupted by maximal contractions and brief rest periods. Despite the induced central fatigue, as tested with the MVC-superimposed twitch technique, and substantial peripheral fatigue, only minor effects of the previous fatigue test were seen for the contralateral hand. No significant influence was found on endurance time, the perceived effort for maintaining 30% MVC force or the MVC-superimposed twitch. Thus, our fatigue protocol induced both central and peripheral fatigue but only minor cross-over effects of fatigue were found for the homologous contralateral muscle.

縦方向溶接継手の疲労強度に与えるブローホールの影響に関する確率的検討

The influence of blowholes on the fatigue strength of members with longitudinal welded joints was investigated by probabilistic approach. Random variables and parameters used were blowhole size, member length, probability of fatigue crack occurrence from blowholes, distribution of stress range and parameter C in Paris's law. Probabilistic functions of these variables were given from the results of previous fatigue tests or field measurements. By parametrical analysis, the influences of the above random valiables on the fatigue strength of longitudinal welded joints were evaluated quantitatively.

Elucidation of Fracture Mechanisms of a Fatigued Chopped Strand Type CFRP by Acoustic Emission Method.

The fracture mechanisms in tensile loading of a fatigued chopped strand carbon fiber. reinforced thermoplastic (CFRP) are examined from the view points of AE count rate, amplitude distribution, and frequency analysis, and compared with those for a virgin specimen. SEM and SAM observations have also carried out. It is confirmed that the peak in the amplitude distribution of AE signals shifts to the higher value side with an increasing of the load and the characteristic relates to the degree of fatigue damage in the previous fatigue test. The phenomenon corresponds to debonding in the chopped tape layer, resin cracking and fiber breaking or pull out of the strand tape, and also recognized the reinforced effect with the strand tape and the fracture mechanisms.

Fatigue Strength of Riveted Bridge Members

Available experimental data from more than 1,200 previous fatigue tests and some fatigue and fracture tests on full-scale members are compiled and examined in conjunction with the details and measured live load stresses in riveted bridges. It is found that the type of riveted detail does not significantly affect fatigue resistance, that AASHTO fatigue strength category D is a reasonable lower bound for the initial fatigue crack development, and that the fatigue strength of a riveted built-up member effectively exceeds the category C resistance curve. It is also found that the primary members in riveted highway bridges seldom are subjected to stress ranges that exceed the category D fatigue limit, and thus are not likely to develop fatigue cracks. The riveted details most likely to develop cracks are those subjected to distortion or displacement-induced stresses at connections. Corrosion can reduce the fatigue resistance, but the effect is not critical if the minimum remaining thickness is not less than one-half of the original thickness. Recommendations are made for rating riveted highway bridges for fatigue damage.

An Exploratory Study of Shear Fatigue Behavior of Prestressed Concrete Girders

T he use of pretensioned concrete beams in bridge superstructures has increased dramatically in the past 30 years. At the same time, strength reduction factors and load limits have been increased, effectively reducing load margins for existing bridges. As a result, the limit state of fatigue failure is now a more important consideration in the evaluation of existing bridges and the design of new bridges. At the present time, engineers have few guidelines to follow for fatigue design of pretensioned concrete members. This paper describes the results of an exploratory investigation undertaken in the Phil M. Ferguson Structural Engineering Laboratory at The University of Texas at Austin to gain a better understanding of the shear frtigue behavior of pretensioned concrete girders. At present, little experimental research has been conducted on shear fatigue. The authors are unaware of any previous shear fatigue tests on full scale specimens designed according to present design specifications. The present investigation was very limited in scope, involving tests of only three full scale girder specimens. Obviously, the wide range of variables actually present in pretensioned bridge girder usage could

Fatigue of Eight‐Year Weathered A588 Steel Stiffeners in Salt Water

Bare, exposed, weathering steel structures have lower fatigue strength than painted steel structures. This finding is based on the results of 36 tests in which transverse stiffener specimens are weathered for eight years and then stresscycled in air or in 3% salt water. The results are compared with those from 1,565 previous fatigue tests of specimens weathered up to eight years and than stresscycled in air. Reductions in allowable stress range are recommended for bare, exposed, weathering steel for bridges in environments of medium corrosivity.