Evaluation Of Fatigue Strength Research Articles

Fatigue and Ultimate Strength Evaluation of GFRP-Reinforced, Laterally-Restrained, Full-Depth Precast Deck Panels with Developed UHPFRC-Filled Transverse Closure Strips

A depth precast deck panel (FDDP) is one element of the prefabricated bridge element and systems (PBES) that allows for quick un-shored assembly of the bridge deck on-site as part of the accelerated bridge construction (ABC) technology. This paper investigates the structural response of full-depth precast deck panels (FDDPs) constructed with new construction materials and connection details. FDDP is cast with normal strength concrete (NSC) and reinforced with high modulus (HM) glass fiber reinforced polymer (GFRP) ribbed bars. The panel-to-girder V-shape connections use the shear pockets to accommodate the clustering of the shear connectors. A novel transverse connection between panels has been developed, featuring three distinct female-to-female joint configurations, each with 175-mm projected GFRP bars extending from the FDDP into the closure strip, complemented by a female vertical shear key and filled with cementitious materials. The ultra-high performance fiber reinforced concrete (UHPFRC) was selectively used to joint-fill the 200-mm transverse joint between adjacent precast panels and the shear pockets connecting the panels to the supporting girders to ensure full shear interaction. Two actual-size FDDP specimens for each type of the three developed joints were erected to perform fatigue tests under the footprint of the Canadian Highway Bridge Design Code (CHBDC) truck wheel loading. The FDDP had a 200-mm thickness, 2500-mm width, and 2400-mm length in traffic direction; the rest was over braced steel twin girders. Two types of fatigue test were performed: incremental variable amplitude fatigue (VAF) loading and constant amplitude fatigue (CAF) loading, followed by monotonically loading the slab ultimate-to-collapse. It was observed that fatigue test results showed that the ultimate capacity of the slab under VAF loading or after 4 million cycles of CAF exceeded the factored design wheel load specified in the CHBDC. Also, the punching shear failure mode was dominant in all the tested FDDP specimens.

Fatigue crack extension mechanism and mode-type analyses of martensitic steels for proposing fatigue strength evaluation method: Example of 18% Ni BCC martensitic steel

The fatigue properties of martensitic steels tend to differ significantly from those of low- and medium-strength steels. Even if the hardness is the same, the fatigue strength varies substantially depending on the microstructure. Thus, for using martensitic steel rationally and developing materials with high fatigue strength, it is desirable to establish a fatigue strength evaluation method that can consider the microstructural effects on fatigue properties. For this purpose, 18% Ni bcc martensitic steel was used as a model metal to conduct rotating-bending fatigue tests in this study. The fatigue crack behavior on the smooth specimen surface was examined, and the fracture surface morphology on both sides of the broken specimen and the microplastic strain distribution near the fatigue crack tip were analyzed. The results clarified the mechanism underlying fatigue crack extension (FCE). The analytical results revealed three types of FCE mechanisms dependent on the stress amplitude, stress state (i.e., plane stress or plane strain), and martensitic microstructure. Considering these mechanisms, a unique stress–life curve was predicted, and a particular fatigue crack shape and fractography were confirmed. The material indices were speculated to be the representative properties of martensitic steels.

Defect-based fatigue crack nucleation and strength evaluation of additively manufactured TiC/Ti6Al4V titanium matrix composite at different temperatures

In mechanical applications, defect-based fatigue cracking is a significant strength-limiting failure mode of additively manufactured composites that is not yet fully understood in the service environment. In this paper, axial loading tests were carried out at 25 ℃ and 450 ℃, and then the effects of temperature on the long-life fatigue properties of the TiC-reinforced Ti6Al4V composite fabricated by Laser Powder Bed Fusion (LPBF) were investigated by combining the techniques of electron backscatter diffraction, X-ray computed tomography, and 3D morphological reconstruction. With the increase in temperature, the fatigue strength of the LPBF TiC/Ti6Al4V composite decreases significantly. The main causes of the interior failure at both temperatures are the inhomogeneous hardening zone (IHZ) formed by TiC agglomeration and the pore defect generated during the manufacturing process. The presence of brittle IHZ and pores causes stress concentration, which leads to crack nucleation. When a crack reaches the specimen surface, the combined effects of temperature and oxygen accelerate the ensuing crack propagation at high temperature. Based on the temperature effect, material properties, and the statistical distribution of defects, a model has been developed to predict the P-S-N curves at both temperatures. This model performed well in estimating the fatigue strength at 109 cycles. These findings provide new insights into the defect-related fatigue failure mechanisms and strength evaluation of the LPBF TiC/Ti6Al4V composite at different temperatures.

Investigation of fatigue strength evaluation of welded structure on spirally welded tank wagon via finite element analysis

Investigation of fatigue strength evaluation of welded structure on spirally welded tank wagon via finite element analysis

Influence of Chemical Composition on Structure and Mechanical Properties of Vacuum-Carburized Low-Alloy Steels.

This study presents research results concerning the vacuum carburizing of four steel grades, specifically conforming to European standards 1.7243, 1.6587, 1.5920, and 1.3532. The experimental specimens exhibited variations primarily in nickel content, ranging from 0 to approximately 3.8 wt. %. As a comparative reference, gas carburizing was also conducted on the 1.3532 grade, which had the highest nickel content. Comprehensive structural analysis was carried out on the resultant carburized layers using a variety of techniques, such as optical and electron scanning, transmission microscopy, and X-ray diffraction. Additionally, mechanical properties such as hardness and fatigue strength were assessed. Fatigue strength evaluation was performed on un-notched samples having a circular cross-section with a diameter of 12 mm. Testing was executed via a three-point bending setup subjected to sinusoidally varying stresses ranging from 0 to maximum stress levels. The carburized layers produced had effective thicknesses from approximately 0.8 to 1.4 mm, surface hardness levels in the range of 600 to 700 HV, and estimated retained austenite contents from 10 to 20 vol%. The observed fatigue strength values for the layers varied within the range from 1000 to 1350 MPa. It was found that changing the processing method from gas carburizing, which induced internal oxidation phenomena, to vacuum carburizing improved the fatigue properties to a greater extent than increasing the nickel content of the steel.

Framework for a finite element method-based simulation approach to fatigue assessment of welded joints using the 4R method

The increased tensile strength capacity of high-strength steels (HSS) can be utilized fully in static loads, for fluctuating loads, however, more detailed analysis of design and manufacturing is needed. This study presents a framework for investigating utilization of the finite element method (FEM) in multiparametric 4R method-based fatigue evaluation. More specifically, the aim of the current study is to produce a concept for determining the parameters of the 4R method using FEM, thus providing a tool for evaluating fatigue strength related factors numerically. The study examines gas metal arc welded (GMAW) longitudinal gusset joints made of HSS S700MC Plus. The simulation is carried out as a sequentially coupled welding analysis that includes material condition changes in the HAZ and the fluctuating response as a restart analysis. Experimental measurement is performed for comparison with the results of the numerical model in the intermediate stages of the analysis process, and in the final stage as regards fatigue life. The experimental and simulated sub-results are consistent, and the estimated fatigue lives are in relatively good agreement with the experimental fatigue results. The numerical method thus provides a tool to predict fatigue related factors considered in 4R to evaluate fatigue life of welded joints.

Numerical and experimental fatigue strength evaluation of thin-walled aluminum components for aerospace application manufactured by roll forming

The design of structural components for use in commercial aircraft places high demands on the safety under static and cyclic loading conditions during the total operating time. With immerging innovative developments in the production of thin-walled sheet metal components, savings in energy consumption and material are achievable by switching from metal-cutting production to forming operations. As the forming process has an impact the local material properties due to resulting residual stress state, cold working and surface finish, the fatigue life estimation requires the consideration of the forming history.The structural component under consideration from aluminum alloy EN AW-7475 T761 is manufactured by automated, robot-assisted roll forming. Potentially existing residual stresses are determined via process simulation of the angled profile utilizing commercial finite element solver LS-Dyna®. The fatigue life assessment is carried out using the Local Strain Approach for different loading conditions.

Development of a small-punch-fatigue test method to evaluate fatigue strength and fatigue crack propagation

Development of a small-punch-fatigue test method to evaluate fatigue strength and fatigue crack propagation

Probabilistic fatigue strength assessment of cross-ply laminates: Exploring effects of manufacturing defects through a two-scale modeling approach

The study presents a two-scale modeling approach allowing for an efficient fatigue strength evaluation on a macro scale considering a micro-mechanical defect characterization of a Carbon Fiber Reinforced Polymer (CFRP) material. The modeling approach integrates a macro model with the effective elastic properties from micro-mechanical simulations considering voids. This enables the analysis of defects’ influence on material fatigue strength using a probabilistic weakest link approach. A CFRP laminate with a cross-ply layup was investigated. Two simulation case studies demonstrate the effect of void content and size on the characteristic fatigue strength. An experimental investigation was conducted testing the laminates in tension–tension fatigue verifying the predicted numerical behavior. The numerical models identify a difference in the characteristic fatigue strength consistent with the fatigue test results. It is numerically concluded that the investigated CFRP material’s fatigue strength is affected by the presence of voids and even with only a slight difference in the global void volume fraction a scatter in fatigue strength is identified.

A comparative study of Glinka and Neuber approaches for fatigue strength assessment on 42CrMoS4‐QT specimens

AbstractIn fatigue strength assessment, the methods based on ideal elastic stresses according to Basquin and the less established method based on elastic‐plastic stress quantities according to Manson, Coffin and Morrow are applied. The former calculates loads using linear‐elastic stresses, the latter requires elastic‐plastic evaluation parameters, such as stresses and strains. These can be determined by finite element analysis (FEA) with a linear‐elastic constitutive law, and subsequent conversion to elastic‐plastic loads, using the macro support formula by Neuber. In this contribution, an alternative approach to approximate elastic‐plastic parameters proposed by Glinka is compared to the the strain‐life method using Neuber's formula, as well as the stress‐life method of Basquin. Several component tests on 42CrMoS4‐QT specimens are investigated. To determine the input data for the fatigue strength evaluations, the entire test setup is computed by FEA. The nodal displacements from these validated full‐model simulations are used as boundary conditions for a submodel simulation of a notch, whose results serve as input for the fatigue strength assessments. It is shown that all approaches provide a reliable assessment of components. Our key result is that the strain‐life method using the concept by Glinka for notch stress computation, yields improved results in fatigue strength assessments.

Fatigue strength evaluation of case‐hardened components combining heat‐treatment simulation and probabilistic approaches

AbstractIn order to raise the hardness and strength of the surface layer of mechanical components and induce favorable residual compressive stresses, case‐hardening procedures have become established in the heat treatment of steel. In this work, a calculation concept for the fatigue strength of components that have been case‐hardened through carburizing heat treatment is being developed. The residual stress and the load stresses in complex‐shaped, carburized materials are determined using a finite element (FE) model. The fatigue limit of the components is derived using probabilistic methods and taking into account hardness gradients, residual stresses, and non‐metallic inclusions. The model is validated with available axial bending fatigue test data and then used to predict the rotating bending fatigue limit of samples with various geometries and heat‐treatment conditions. This work demonstrates the capability of combining probabilistic and FE‐based modeling to represent complex interactions between variables that affect the fatigue of heat‐treated components, such as steel cleanliness, notch shape, case‐hardening depth, or loading conditions.

Fatigue strength evaluation of scale railway axle with surface defect considering mean stress effect

In order to evaluate the notch fatigue strength of transition groove in railway axle, a series of fatigue tests were conducted on small specimens and press-fitted axles containing surface defects. Based on the experimental and finite element (FE) analyses, a novel method considering mean stress effect was proposed to evaluate the fatigue strength of scale railway axle with surface defect. It is found that press-fitted axles exhibit significantly lower notch fatigue strength than small specimens. Furthermore, the theory of critical distance (TCD) provides a good correlation between the notch fatigue strength of small specimens and experimental results. FE analyses revealed that the press-fitting reduces the fatigue strength of the transition groove through increasing stress concentration and introducing a mean tensile stress that decreases with an increase in the applied loading. To account for the mean stress effect, the axial stress at the groove is corrected as an equivalent stress amplitude at R = -1 based on Goodman relation. Through the combination of TCD and Goodman relation, an estimated fatigue strength with an error of less than 11 % can be achieved for the scale railway axle with surface defect.

Numerical Analysis and Experimental Investigation of High Cycle Fatigue Behavior in Additively Manufactured Ti–6Al–4V Alloy

Additive Manufacturing (AM) of the Ti–6Al–4V alloy has gained significant importance across various industries, including biomedical, aerospace, cellular, and land vehicle applications, due to its numerous benefits. The certification of performance and reliability of AM materials, particularly for critical applications, heavily relies on evaluating fatigue strength. In this study, a numerical analysis based on the finite element method is presented to predict the High Cycle Fatigue (HCF) behavior of AM Ti–6Al–4V alloy. The investigation focuses on exploring the sensitivity of material fatigue life to surface roughness and Ultimate Tensile Strength (UTS). Uniaxial tensile and High Cycle Fatigue (HCF) tests were conducted on Ti–6Al–4V alloy samples extracted from rectangular walls manufactured using the Laser Metal Deposition (LMD) process. The walls were surface machined prior to sample extraction. Porosity and surface roughness measurements were performed on the samples. Numerical simulations of the HCF tests were carried out, considering various surface roughness ranges and UTS values. The numerical results were then compared to experimental data. The findings consistently demonstrated that higher surface roughness led to a shorter fatigue life, while higher UTS values resulted in a longer fatigue life. The numerical solutions aligned with the experimental results, indicating the efficacy of the finite element method in predicting the fatigue behavior of AM Ti–6Al–4V alloy. These insights contribute to a better understanding of the relationship between surface roughness, UTS, and fatigue life of Ti–6Al–4V alloys manufactured by AM.

Numerical analysis of fatigue strength for ultra-large ships considering springing

Due to the low stiffness of ultra-large ships, the effect of springing becomes more obvious. The traditional quasi-static spectral method (QSM) ignores the coupling effect of hydrodynamic load and hull elastic characteristics, so it is unable to solve the problem of fatigue strength considering springing. To solve the problem and investigate the impact of springing response on fatigue, the stress mode superposition spectral method (SSM) suitable for ultra-large ships is proposed. The numerical analysis is performed on a real ship as an example. The results show that: Fatigue stress response generates new peaks at the high-frequency regions when considering the effect of springing, and fatigue damage is greatly increased. The degree of influence of springing response on fatigue strength is related to wave incident angles and sea conditions. This method has reference significance for the evaluation of fatigue strength of ultra-large ships considering springing effects.

Fatigue strength evaluation by measurable stresses for root cracks in U-rib to deck welded joints of orthotropic steel decks

Fatigue strength evaluation by measurable stresses for root cracks in U-rib to deck welded joints of orthotropic steel decks

Stress amplification effect and fatigue strength evaluation of marine thin plate welded structure considering welding deformation: Theoretical and experimental analysis

Due to the low bending stiffness of thin plate welded joints, welding deformations such as welding dislocation, welding angle deformation and initial welding deformation are easy to occur in the welding process. The existence of these deformations will cause additional stress concentration effect and reduce the fatigue performance of thin-plate welded structures. Therefore, the influence of various welding deformations should be considered when evaluating the fatigue strength of the welded joints of thin plates. Combined with the test data, the calculation formula of stress amplification factor considering various welding deformations proposed by this paper is compared with the calculation formula in the existing literature and finite element calculation results. Moreover, the analytical formula is applied to the fatigue assessment of 5059 aluminum alloy welded joints. According to the evaluation results, it is found that the structural stress method and equivalent structural stress method based on the proposed bending stress amplification coefficient formula have good evaluation results for aluminum alloy thin plate specimens with welding deformations. Fatigue strength class curves suitable for thin plate aluminum alloy welded joints corresponding to different fatigue evaluation methods are further suggested.

2700kW主機関クランク軸に発見された溝状欠陥の疲労強度評価

A grooved defect of 0.43mm depth x 7mm width x 370mm length = 1/3 circle caused on crank shaft of 2700kW main diesel engine was found during CMS inspection of special survey dock. At first permanent repair by machining the crank pin to remove 1.0mm depth all around with fitting oversized crank pin metal have been discussed. However it is expected for 3 months at least to make up oversize crank pin metal. So, the vessel was sailed out after removing notches from the defect carefully with confirming safety condition by stress calculation with fatigue strength evaluation of the crank shaft contained the defect and checking lubricating flow condition. This time, its summary is shown in this paper.

Experimental Evaluation of Fatigue Strength of AlSi10Mg Lattice Structures Fabricated by AM

There is evidence that Additive Manufacturing (AM) plays a crucial role in the fourth industrial revolution. The design freedom provided by this technology is disrupting limits and rules from the past, enabling engineers to produce new products that are otherwise unfeasible. Recent developments in the field of Selective Laser Melting (SLM) have led to a renewed interest in lattice structures that can be produced non-stochastically in previously unfeasible dimensional scales. One of the primary applications is aerospace engineering where the need for light weights and performance is urgent to reduce the carbon footprint of civil transport around the globe. Of particular concern is fatigue strength. Being able to predict fatigue life in both LCF (Low Cycle Fatigue) and HCF (High Cycle Fatigue) is crucial for a safe and reliable design in aerospace systems and structures. In the present work, an experimental evaluation of compressive–compressive fatigue behavior has been performed to evaluate the fatigue curves of different cells, varying sizes and relative densities. A Design of Experiment (DOE) approach has been adopted in order to maximize the information extractable in a reliable form.

Evaluation of Cyclic Fatigue and Torsional Strength of Three Different Thermally Treated Reciprocating Nickel-Titanium Instruments

Objectives. This article's objective was to assess the reciprocating single-file systems Reciproc Blue 25.08 and Pro design R 25.06's cyclic and torsion fatigue resistance. The systems Reciproc Blue R25 (RB #25.08 taper), Prodesign R (PDR #25.06 taper), and WaveOne Gold (WOG #25.07 taper) (n = 20) were utilized to make sixty reciprocating instruments. The period to breakdown in an artificial stainless-steel canal with a 60° angle of curvature and a 5-mm radius was measured during cyclic fatigue resistance testing (n = 10). The torque and angle of rotation at failure of new instruments (n = 10) were assessed during the torsional test (ISO 3630-1) in the area 3 mm from the tip. Scanning electron microscopy was also used to view each fragment's shattered surface (SEM). In addition, a supplementary examination was performed to measure the cross- sectional area of each instrument 3 and 5 mm from the tip. The data were analyzed using one-way ANOVA and Tukey’s test, and the level of significance was set at 5%. Cycle Fatigue Resistance scores for PDR 25.06 were much higher (P 0.05). Both WOG 25.07 and RB 25.08 showed less resistance to fatigue (P 0.05). Based on the torsional analysis, PDR 25.06 had weaker torsional strength (P 0.05). No changes were found with RB 25.08 and WOG 25.07 (P > 0.05). PDR 25.06 showed higher angular rotation values than RB 25.08 and WOG 25.07. (P 0.05). Greater angular rotation was seen in both WOG 25.07 and RB 25.08. (P 0.05). The cross-sectional area analysis revealed that PDR 25.06 had the smallest cross-sectional areas at 3 and 5 mm from the tip (P 0.05). In comparison to RB 25.08 and WOG 25.07, PDR 25.06 had the highest cyclic fatigue resistance and angular rotation until fracture. Additionally, torsional strength was higher in RB 25.08 and WOG 25.07 than PDR 25.06. Clinical applicability in endodontic practise, reciprocating instruments that have undergone thermal treatment are used to prepare the root canals of canals that are curved and constrained; as a result, these instruments must exhibit high flexibility and suitable torsional strength to reduce the risk of instrument deformation.

Improving of mechanical properties of AMg5 aluminum alloy obtained by additive growth and hardening technologies

The results of the study of the AMg5 alloy obtained by additive growing of products using the WAAM technology are presented. The evaluation of mechanical properties and fatigue strength and durability of the metal was carried out. The features of the propagation of micro- and macrocracks in the material during fatigue loading are studied. It is shown that the vibration effect on the 3D printing process provides an increase in the mechanical proper ties of the aluminum alloy.