Fatigue Life Properties Research Articles

On the Sources of Discrepancies Between Grain Size Measurements

Accurate quantification of grain size in polycrystals is extraordinarily important for quality assurance and the development of structure-property relationships, as grain size affects nearly all engineering properties of structural alloys, from strength and fatigue life to corrosion resistance and thermal conductivity. Despite nearly a century of the existence of standards for measuring grain size, issues persist in obtaining consistent grain size measurements across several techniques. Of particular interest is comparing optical microscopy or scanning electron microscopy on an etched surface with mapping of crystal orientations using electron backscatter diffraction (EBSD). In this work, discrepancies between methods in the ASTM E 112 and ASTM E 2627 standards are explored through simulated measurements on synthetic microstructures. It is concluded that a small but systematic discrepancy exists between planimetric and lineal intercept-based approaches, and a new empirical relationship between the ASTM grain size number G and lineal intercepts is proposed.

Progressive fatigue modelling of composite pipes with a hole

Composite pipes are increasingly used in demanding applications thanks to their light weight and corrosion resistance. To manage their integrity, tools able to predict their fatigue life and residual properties under cyclic loads are required. A finite element progressive fatigue model was applied to filament-wound composite pipes with a hole submitted to tensile cyclic fatigue. The fatigue model combined continuum damage mechanics for intra-laminar failure mechanisms and cohesive zone modelling for inter-laminar and selected macroscopic cracks. A linear fatigue damage accumulation law was used along with an empirical sudden-death residual strength model, relying solely on the material S-N curve. The fatigue simulation was conducted by an external cycle-jump procedure. After calibration on one load level, the model was able to describe the fatigue life at other load levels within one standard deviation (0.63 decade) of the experiments and resulted in a S-N curve slope of −0.084 while the experimental one was −0.072.

Fatigue behavior of polymethyl methacrylate/acrylonitrile butadiene styrene blends including blend composition, stress ratio, frequency, and holding pressure effects

In engineering applications, polymer materials are expected to exhibit superior fatigue life and balanced mechanical properties as essential performance criteria. The blending method is an important alternative in improving the performance criteria of ABS polymer in service. Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), and Dynamic Mechanical Analysis (DMA) methods were used for characterization. The effects of the PMMA fraction on the mechanical and fatigue behavior of PMMA/ABS blends were investigated by tensile and fatigue tests. Also, the influence of blend composition, stress amplitudes, stress ratio, holding pressure, and loading frequency on fatigue life is considered. The study improved yield strength, tensile strength, and elongation at break values of blends compared to ABS. In addition, 115 % and 75 % improvements were achieved in fatigue cycles at high and low-stress amplitudes with blends, respectively, for tension/tension loading. Similar improvements were obtained for fully reverse loading at 218 %. Thus, it was determined that the PMMA/ABS blend exhibited superior fatigue life in both tension/tension and fully reverse loading situations. Finally, it has been understood that PMMA/ABS blends can be designed to have mechanical properties and fatigue life behavior that can meet different requirements in conditions for engineering applications.

THE CORROSION INHIBITION EFFECT ON THE ALUMINUM ALLOY AZ91C'S FATIGUE BEHAVIOR IN THE SALINE ENVIRONMENT

Investigations were made into the fatigue in the magnesium alloy AZ 91C cast in corrosive fluids and air at varied NaCl solution concentrations. Fatigue specimens will be subjected to surface stress testing in corrosive conditions with a stress amplitude of 75 MPa both after and before coating. To comprehend the behavior of the magnesium material, its fatigue life, corrosion product (X-ray spectra), and fracture properties will be examined. The corroding medium (NaCl) has been found to significantly shorten the fatigue life of the magnesium alloy AZ91C. Chemical conversion treatment was applied to the AZ91C alloy to improve corrosion resistance and corrosion fatigue resistance. MgSnO3 was found in the XRD patterns of the stannite-treated AZ91C alloy, and this treatment slightly improved the alloy's corrosion resistance in an alkaline stannite solution with a pH of 7. H2O and SEM images demonstrate that chloride ions can penetrate the substrate through porous structures.

Design Analysis and Optimization of Coil Spring for Three-Wheeler Vehicles Using Composite Materials

The quest for lightweight, efficient, and corrosion-resistant coil springs for vehicle suspension systems has led to the exploration of alternative materials beyond traditional steel. This study delves into the potential of composite materials, particularly carbon/epoxy and carbon/carbon nanotube/epoxy, as replacements for conventional steel coil springs in light vehicles. Through a comprehensive analysis of mechanical properties under static and dynamic loading conditions, the study demonstrates the superior performance of composite springs compared to their steel counterparts. After optimization, the deflection of the carbon/carbon nanotube/epoxy and carbon/epoxy springs decreased to 15.003 mm and 18.703 mm, respectively, and the maximum shear stress decreased by 64.63% and 62.2%, respectively. Likewise, strain energies increased to 2.3644 and 3.5616, respectively. The springs were also studied under dynamic conditions, and the result showed these springs have the ability to perform in dynamic conditions. The carbon/carbon nanotube/epoxy composite emerged as the frontrunner, exhibiting remarkable improvements in shear stress, fatigue life, strain energy, and deformation properties. The study highlights the ability of carbon/carbon nanotube/epoxy composite springs to significantly reduce weight, enhance efficiency, and extend fatigue life, making them a promising alternative for next-generation vehicle suspension systems.

Evaluation on the fatigue and self-healing properties of aged and rejuvenated SBS-modified asphalt

To investigate the fatigue and self-healing properties of aged and rejuvenated SBS-modified asphalt, soybean oil (SBO), epoxidized soybean oil (ESO), and commercial rejuvenators (LBS) were selected as asphalt rejuvenators. The fatigue performance of the asphalt was assessed through a time sweep procedure using a dynamic shear rheometer (DSR) instrument. Subsequently, a series of fatigue-healing-fatigue tests were conducted with varying healing times and damage degrees to analyze the self-healing characteristics of the asphalt. The rejuvenation and self-healing mechanisms were elucidated through a fluorescence microscope, Fourier transform infrared spectroscopy (FTIR), and thin-layer chromatography with flame ionization detection (TLC-FID) tests. The results revealed that the fatigue life of aged SBS asphalt deteriorated by more than 17% compared to unaged asphalt, and the self-healing properties were also weakened. However, both the fatigue life and self-healing properties could be significantly restored through the addition of rejuvenators, with SBO exhibiting the most pronounced effect in their restoration, followed by LBS and ESO. Furthermore, the self-healing capacity of the asphalt was notably affected by both the healing time and damage degree. Microstructure test results showed that in aged SBS-modified asphalt, lighter components dissipated, and the polymer deteriorated, contributing to the decline in self-healing performance. The presence of a substantial quantity of lightweight components in SBO expedited wetting and molecular diffusion at the damaged interface within the asphalt, thereby restoring the self-healing properties of the aged asphalt.

An investigation of relationships between statistical dispersion of crankshaft’s fatigue properties and initial damage

Premature failure due to fatigue would occasionally happen even in a well-designed crankshaft. The microstructural nonuniformity (including micro-defects) plays an essential role in the premature failure due to fatigue, which can lead to the scatter of strength and fatigue life properties. In this paper, the statistical distribution of initial damage corresponding to microstructural nonuniformity has been introduced to uniformly characterize scattering behaviors of tensile strength, fatigue life and impact energy in sampling tests of crankshafts. The goal of this study is to investigate quantitative relationships between the dispersion of initial damage and scattering behaviors of the above sampling tests, so that dispersion properties of a crankshaft can be determined only by relatively simple experiments. By impact sampling tests and several single-throw crankshaft fatigue tests, probability density functions of initial damage have been determined for two crankshafts provided by different manufacturers. It is found that the fatigue reliability of a crankshaft depends on its actual dispersion properties. For a crankshaft with large dispersion of initial damage, the safety factor in the fatigue strength design should be sufficiently large to prevent its premature failure due to fatigue, rather than the one directly recommended in the design manual.

Mechanical Properties of Open-Graded Asphalt Friction Course Mixtures with Basic Oxygen Furnace Steel Slag as Coarse Aggregates

Open-graded asphalt friction course (OGAFC) is an asphalt course constructed over a dense-graded and impermeable surface to allow quick drainage of surface water runoff and enable reduction of hydroplaning and splash and spray. OGAFC mixtures demand high-quality aggregates to perform the intended functions while transferring traffic loads to the underlying layer. Steel slag is a byproduct generated during steel production, and large quantities are unutilized in steel-producing countries, including India. This study evaluated the mechanical performance properties of OGAFC mixtures using basic oxygen furnace (BOF) steel slag as replacement for coarse aggregates at percentages of 0%, 25%, 50%, 75%, and 100%. OGAFC mixtures with two types of modified asphalt binders and five percentage replacements of coarse natural aggregates with BOF steel slag were fabricated. The mechanical performance of the OGAFC mixtures was evaluated in terms of rutting resistance (dynamic creep test and Hamburg wheel tracking device test), cracking potential (indirect tensile strength, cracking tolerance index, and semicircular bending test), fatigue life (indirect tensile fatigue test), and modulus properties (indirect tensile stiffness modulus and resilient modulus). The test results indicated that the use of BOF steel slag not only improved the performance of OGAFC mixtures in terms of rutting resistance, cracking potential, and modulus properties, but also increased the fatigue life of the OGAFC mixes. OGAFC mixes up to 100% BOF steel slag content exhibited superior performance compared with the mixtures with natural aggregates.

A Critical Review on Improving the Fatigue Life and Corrosion Properties of Magnesium Alloys via the Technique of Adding Different Elements

Magnesium is the eighth-most abundant element in the world and its alloys have a widespread application in various industries such as electronic and transport (i.e., air, land, and sea) engineering, due to their significant mechanical properties, excellent machinability, high strength to weight ratios, and low cost. Although monolithic Mg metal is known as the lightest industrial metal (magnesium density is 30% less than the density of the aluminum, and this unique property increases the attractiveness of its usage in the transportation industry), one of the significant limitations of magnesium, which affects on its applications in various industries, is very high reactivity of this metal (magnesium with an electronegativity of 31.1 can give electrons to almost all metals and corrodes quickly). To overcome this problem, scholars are trying to produce magnesium (Mg) alloys that are more resistant to a variety of loads and environmental conditions. In this regard, Mg alloys include well-known materials such as aluminum (Al), Zinc (Zn), Manganese (Mn), Silicon (Si), and Copper (Cu), etc., and their amount directly affects the properties of final products. In the present review paper, the authors attempted to present the latest achievements, methods, and influential factors (finish-rolling, pore defects, pH value, microstructure, and manufacturing processes, etc.) on the fatigue life and corrosion resistance of most significant Mg alloys, including AM50, AM60, AZ31, AZ61, AZ80, AZ91, ZK60, and WE43, under various conditions. The summarized results and practical hints presented in this paper can be very useful to enhance the reliability and quality of Mg-made structures.

Design and Optimization of Tool-Embedded Thin-Film Strain Sensor Substrate Structure

With the intelligent tool cutting force measurement model as the engineering background, the selection, design, and optimization of the substrate structure of the tool-embedded thin-film strain sensor are studied. The structure of the thin-film strain sensor is studied, and the substrate structure design is divided into function area structure design and connection area structure design. Establishing the substrate structure library of the sensor, we subdivide the library into six layouts of function area infrastructure and five layouts of connection area infrastructure. Taking the sensitivity, fatigue life, and comprehensive mechanical properties of the substrate structure as the design indexes, based on the statics theory, the functional relationship between the structural parameters and the deflection of the six layouts of the substrate function area is established; based on the dynamics theory, the functional relationship between the parameters and the natural frequency of six layouts of the function area is established; based on the coupling of structural statics design theory and dynamics design theory, the evaluation method for the comprehensive performance of the parameters of six layouts of the function area is established. Based on the function area structure, five connection area structures are designed for comprehensive performance analysis. The structural sensitivity of the substrate function area design and optimization is expanded 1.75 times, and the comprehensive performance is expanded 1.53 times. The sensitivity of the connection area design and optimization is expanded 2.3 times, and the comprehensive performance is expanded 1.72 times. The structure is optimized according to the structural stress characteristics, the design, selection, and optimization process of the substrate structure summarized herein, and five design criteria of the substrate structure are proposed.

The porosity distribution of nickel‐base single‐crystal superalloy DD5 and its fatigue life property

AbstractThe porosity of nickel‐base single crystals (NBSXs) is still an unavoidable casting problem that has a significant influence on the fatigue life of NBSXs. In order to quantify the porosity effect, a porosity‐distribution‐related life prediction method is proposed in this paper. The porosity size in a NBSX was measured, and the size distribution was regressed. The results show that the porosity size that is characterized by Feret's diameter follows a modified logarithmic normal distribution. The relation among the applied stress, porosity size, and lifetime is expressed by using the proposed method. The disperse band of S–N curve is investigated based on the probability distribution of the porosity size. The results show that the predicted S–N curve agrees well with the experimental data.

The effects of building position on surface and fatigue of DED-arc steel components

Recently, additive manufacturing (AM) of structural metallic components is analyzed regarding its potential use by industry and research. Next to the development of manufacturing processes, the mechanical properties are under investigation today. One of the quality measures of metallic components is the surface topography. DED-arc processes (direct energy deposition) result in relatively coarse surfaces, characterized by a distinct waviness with wave amplitudes in the mm-range. This is enhanced when applying horizontal building position in comparison to vertical position. Next to increased waviness, the load-bearing net cross sections are reduced as well. The surface topography determines the fatigue life properties of metallic components. While stress raising surface effects are generally well understood and fatigue (Structures 31: 576–589, 2021) of welded metals is established well, the fatigue behaviour of additively manufactured components is less investigated yet. In order to define surface quality levels for DED-arc components, the effects of surface topography on mechanical performance need to be understood. This article presents the manufacturing of high strength steel test coupons by the DED-arc process. The process parameters were varied with regard to the building position and different levels of surface quality were generated. The surfaces of different specimens were characterized and fatigue tests were conducted. The results were used to derive the surface influence on both, the effective load-bearing wall thickness and notch effects induced by the layer-by-layer building approach. A correlation between building position, surface waviness and fatigue strength was proven. In general, higher waviness resulted in reduced effective wall thickness and lowered fatigue strength. A difference in fatigue strength at 2 million load cycles of 20 to 30% was proven when printing in different building positions. The surface effect can be captured in the design concept when applying the effective notch stress approach with an averaging length of of ρ* = 0.4 mm. The fatigue strength is describable by a design S–N curve FAT160 and a k-value of 4.

Structure and fatigue behavior of electroless plated Ni-Zn-P films using pretreatments, annealing and an applied magnetic field

Electroless ternary Ni-Zn-P films are plated onto a low carbon steel substrate. The surface morphology, microstructure, hardness, fatigue life and corrosion properties of the Ni-Zn-P coatings are respectively determined using scanning electron microscopy, X-ray diffraction, nano-indentation, high-strain low-cycle fatigue and polarization tests. The substrates pretreated using the proposed roughening (15 % H2SO4, 20 min) and activation (10 % H2SO4, 1 min) produce good Ni-Zn-P film deposition. When the annealing temperature reaches 400 °C, the Ni–P-Zn films contain crystalline Ni, FeNi and a precipitation Ni3P structures phase. Applied magnetic field improves the film growth rate, mechanical properties and corrosion resistance.

Fatigue Damage Behaviors of TRC-Strengthened RC Beams.

For the investigation of fatigue damage behavior of textile reinforced concrete (TRC)-strengthened RC beams, in this study, eight RC beams were fabricated, and five of them were strengthened with TRC and tested under fatigue loading until failure, using a four-point bending setup. Research parameters included reinforcement ratio, textile ratio, and strengthening methods (single-side and U-wrapped). The failure mode, fatigue life, fatigue deformation, and other properties of TRC-strengthened beams were analyzed. Experimental results revealed that there were two fatigue failure modes for TRC-strengthened RC beams. In the first mode, the textile was snapped, but the steel bars did not rupture. In the second mode, both the textile and steel bars broke. Fatigue failure modes depended on the textile ratio. The TRC-strengthened beam’s fatigue life was significantly higher than the non-strengthened RC beam. At the same textile ratio, the TRC-strengthened beam’s fatigue life using the single-side method was longer than that using the U-wrapped method. With the increase in fatigue loading time, the midspan deflection of the TRC-strengthened beam was developed in three stages, namely rapid development stage, stable development stage, and destabilized development stage. The residual deflection and strain damage accumulation of tensile steel bars of TRC-strengthened beams were significantly reduced with the increase in textile or reinforcement ratios; thus, the beam’s fatigue life was prolonged.

Fatigue Life Estimation Using Single Spot-Welded Joint Fracture Mechanics

The influence of a spot-welded joint on the overlap section of the specimen, which is critical for spot welded joints subjected to uniaxial in plane loads, on fatigue life is explored in this study. This study was carried out using the ANSYS finite element program. The fatigue life properties of spot-welded specimens with various gap values are numerically calculated using a created computer program and several fatigue-life techniques to see how the gap affects the fatigue life of the spot-welded specimens. With rising gap values, it is noticed that maximum stress and strain values increase, resulting in a loss in fatigue life. Maximum stresses and strains, and hence fatigue-life values, are shown to be relatively constant for gap values less than 0.0025mm.

Study on the relationship between fatigue life and rheology of rejuvenated asphalt

The utilization of reclaimed asphalt pavement (RAP) contributes significantly to reducing resource waste and protecting the environment. However, due to the performance of rejuvenator, fatigue cracking has always been one of the important constraint on the development of the reclaimed asphalt pavements. Based on the studies previously conducted by our group, this paper investigated the fatigue properties of waste rubber/oil (WRO) rejuvenated asphalt and common rejuvenated asphalt by dynamic shear rheometer test (DSR), and analyzed the relationship between fatigue life and rheological properties of rejuvenated asphalt. The results indicated that the fatigue life of WRO rejuvenated asphalt is comparatively better than that of common rejuvenated asphalt. Affected by the of waste tire crumb rubber (WTCR), the increase of the proportion of waste tire crumb rubber (WTCR) can improve the elastic recovery ability of rejuvenated asphalt. The fatigue life of rejuvenated asphalt is susceptible to the rate of phase angle change, and the lower the viscoelasticity change rate, the better the fatigue life. There is no obvious direct relationship between the fatigue life of rejuvenated asphalt and the complex modulus.

Effect of fiber hybrid mode on the tension–tension fatigue performance for the pultruded carbon/glass fiber reinforced polymer composite rod

In order to promote the application of fiber reinforced polymer (FRP) rod in bridge engineering, the carbon/glass fiber uniformly dispersed hybrid (UDH) rod with a diameter of 22 mm was developed as the bridge cable through the pultrusion technology. In the present paper, the tension–tension fatigue performances of hybrid rod were investigated with three stress levels of 0.33, 0.44, 0.60 and the fixed stress ratio of 0.4. The fatigue life, stiffness degradation and stress redistribution during the fatigue loading were obtained by linear variable differential transformer (LVDT) and digital image correlation (DIC) method. Furthermore, the fatigue failure mechanism was revealed by microstructure damage analysis. Through the fiber uniformly hybrid technology, the fatigue failure mode of hybrid rod transferred from shell-core debonding to uniformly carbon and glass fiber/resin interface splitting. The positive hybrid effect of fatigue performance was realized to obtain higher fatigue life, stiffness retention and residual mechanical properties. The reliable fatigue life prediction model was developed, and the recommended fatigue limit of present hybrid rod applied for bridge cable was 0.45 at the stress ratio of 0.4 to obtain more than two million fatigue cycles.

Mechanical and fatigue behaviour of artificial ligaments (ALs)

A flexible biologic band, ACL is the most injured and ruptured ligament in the knees of humans and animals. This research aims to produce synthetic anterior cruciate ligaments (ACLs) and compare these ligaments' mechanical and fatigue life properties with the natural ACL and commercial synthetic grafts. Artificial ligaments were designed as a core-sheath type structure. The core consisted of straight, parallel yarns and the sheath was a tubular fabric produced by weaving or braiding techniques from polyester or Vectran® yarns. The mechanical properties of the resulting artificial ligaments (AL) were tested before and after the fatigue test and compared to those of the natural ACL and commercial artificial ACLs in the market. Results showed that all ligaments had sufficient tensile strength, and they retained it after the fatigue test. If constructed sheath and core parts were from the same type of yarns, the breaking load of ligaments was higher. The breaking strain and stiffness of woven structures, particularly with Vectran cores, were better than braided ones. After the fatigue test, the breaking strain and stiffness of AL structures with a braided sheath or polyester core were improved. This finding suggests that to prevent the laxity of knee preconditioning of the ligament is necessary if the fabric structure or yarn inherently has high breaking strain and low stiffness. Overall, this study shows that a variety of suitable candidates for replacing ruptured anterior cruciate ligaments could be developed by carefully combining the fatigue-resistant yarns with leno, narrow, and braided structures.

Cyclic response of high strength fibre reinforced concrete beams with fibre reinforced polymer (FRP) laminates

This paper assesses the cyclic response of high strength concrete beams with externally bonded GFRP laminates reinforced by steel fibre. For the current research work a total of six rectangular beams have been casted. In the preliminary we are used three different percentage of steel fibre 0.5%, 1% and 1.5% from the different tests are conducted in laboratory we were find out the optimum as 1%. One of the beam was worked as control beam as well as the other five have been provided with the steel fibres of having 1% in volume fraction in that 4 beams laminated of 3 mm and 5 mm thickness of CSMGFRP and UDCGFRP. The beams in the cross-section were 150 mm × 250 mm, and 3000 mm long. The beams were tested over a span of 2800 mm, in four-point bending. Under monotonically increasing loading, one beam has been tested and manual readings have been recorded directly in a spreadsheet programme from that load range was fixed from the static ultimate load of the control beam fmin 20% and fmax 60%.The test specimens were subjected to sinusoidal loading at a frequency of 2 Hz. The remaining five beams are test under cyclic loading have been tested and readings have been recorded directly by using MTS793 Flextest software. Adequate data has been collected upon its deformation, strength, fatigue life and failure properties of high-strength concrete beams reinforced with GFRP laminates, and also high-strength concrete beams reinforced with steel fibre. The analysis approaches adopted with this research work comprised sufficient information on deflection, number of cycles, rigidity, number of cracks, crack duration, average crack spacing, energy absorption and failure characteristics for high-strength concrete beams reinforced with externally bonded GFRP laminates under cyclic loading. The findings of the tests performed are thoroughly explained and analyzed.

In-situ warm shot peening on Ti-6Al-4V alloy: Effects of temperature on fatigue life, residual stress, microstructure and mechanical properties

Shot peening (SP) is a matured surface enhancement technique to improve fatigue strength and fatigue lives of cyclically loaded metallic components at room temperature. In order to achieve enhanced beneficial effects beyond SP’s conventional performance, SP has been attempted at elevated temperatures or under tensile stress loading on spring steel with some success. In this work, SP on α/β Ti-6Al-4V alloys has been carried out when they were heated at elevated temperatures up to 400 °C. The effects of such in-situ warm SP on fatigue life of Ti-6Al-4V at different temperatures have been evaluated and correlated with respective development in compressive residual stress distribution, microstructure and hardness. The optimum in-situ warm SP condition was achieved at 100 °C after a trade-off between compressive residual stress relaxation and enhanced grain refinement, both of which are affected by thermal softening but to different degrees.