Tension-compression Fatigue Tests Research Articles

Quasi-static and dynamic mechanical properties of a linoleic acid-modified, low-modulus bone cement for spinal applications

Background Polymethylmethacrylate (PMMA) bone cement is extensively used in spinal procedures such as vertebroplasty and kyphoplasty, while its use in percutaneous cement discoplasty (PCD) is not yet widely spread. A main issue for both application sites, vertebra and disc, is the mismatch in stiffness between cement and bone, potentially resulting in adjacent vertebral fractures and adjacent segment disease. Tailoring the cement modulus using additives is hence an interesting strategy. However, there is a lack of data on the tensile and tension-compression fatigue properties of these cements, relevant to the newly researched indication of PCD. Method A commercial PMMA cement (VS) was modified with 12%vol of linoleic acid (VSLA) and tested for quasi-static tensile properties. Additionally, tension-compression fatigue testing with amplitudes ranging from +/-5MPa to +/-7MPa and +/-9MPa was performed, and a Weibull three-parameter curve fit was used to calculate the fatigue parameters. Results Quasi-static testing revealed a significant reduction in VSLA’s Young’s Modulus (E=581.1±126.4MPa) compared to the original cement (E=1478.1±202.9MPa). Similarly, the ultimate tensile stress decreased from 36.6±1.5MPa to 11.6±0.8MPa. Thus, VSLA offers improved compatibility with trabecular bone properties. Fatigue testing of VSLA revealed that as the stress amplitude increased the Weibull mean number decreased from 3591 to 272 and 91 cycles, respectively. In contrast, the base VS cement reached run-out at the highest stress amplitude. However, the lowest stress amplitude used exceeds the pressures recorded in the disc in vivo, and VSLA displayed a similar fatigue life range to that of the annulus fibrosis tissue. Conclusions While the relevance of fully reversed tension-compression fatigue testing can be debated for predicting cement performance in certain spinal applications, the results of this study can serve as a benchmark for comparison of low-modulus cements for the spine. Further investigations are necessary to assess the clinical feasibility and effectiveness of these cements.

Compressive residual strength of the pultruded glass-fiber composite after tension-compression fatigue

We experimentally determined the decrease of residual compressive strength of the pultruded glass-fiber laminate after tension-compression cyclic loading. The adapted Arcan rig was used for tension-compression fatigue tests. The cyclic load was applied with the critical stress ratio R=−0.87. The residual compressive strength was determined after applying the predefined number of loading cycles with the stress amplitudes of 242 MPa and 173 MPa. The results indicated that the residual compressive strength was reduced about 20% at 77% of fatigue life under the stress amplitude of 242 MPa and at 83% of fatigue life under the stress amplitude of 173 MPa. The microstructural analysis showed that the crack growth path and failure mode depend on the stress amplitude.

Quasi-static and dynamic mechanical properties of a low-modulus bone cement for spinal applications

Background Polymethylmethacrylate (PMMA) bone cement is extensively used in spinal procedures such as vertebroplasty and kyphoplasty, while its use in percutaneous cement discoplasty (PCD) is not yet widely spread. A main issue for both application sites, vertebra and disc, is the mismatch in stiffness between cement and bone, potentially resulting in adjacent vertebral fractures and adjacent segment disease. Tailoring the cement modulus using additives is hence an interesting strategy. However, there is a lack of data on the tensile and tension-compression fatigue properties of these cements, relevant to the newly researched indication of PCD. Method A commercial PMMA cement (VS) was modified with 12%vol of linoleic acid (VSLA) and tested for quasi-static tensile properties. Additionally, tension-compression fatigue testing with amplitudes ranging from +/-5MPa to +/-7MPa and +/-9MPa was performed, and a Weibull three-parameter curve fit was used to calculate the fatigue parameters. Results Quasi-static testing revealed a significant reduction in VSLA’s Young’s Modulus (E=581.1±126.4MPa) compared to the original cement (E=1478.1±202.9MPa). Similarly, the ultimate tensile stress decreased from 36.6±1.5MPa to 11.6±0.8MPa. Thus, VSLA offers improved compatibility with trabecular bone properties. Fatigue testing of VSLA revealed that as the stress amplitude increased the Weibull mean number decreased from 3591 to 272 and 91 cycles, respectively. In contrast, the base VS cement reached run-out at the highest stress amplitude. However, the lowest stress amplitude used exceeds the pressures recorded in the disc in vivo, and VSLA displayed a similar fatigue life range to that of the annulus fibrosis tissue. Conclusions While the relevance of fully reversed tension-compression fatigue testing can be debated for predicting cement performance in certain spinal applications, the results of this study can serve as a benchmark for comparison of low-modulus cements for the spine. Further investigations are necessary to assess the clinical feasibility and effectiveness of these cements.

Fatigue strength of new explosively welded steel-aluminum transition joint used in ships

The paper presents the results of tension-compression fatigue tests of a new steel-aluminum welding transition joint with a titanium Grade 1 interlayer. The new explosive welded transition joint prototype used as a connector in the shipbuilding industry has been developed by the Explomet company situated in Opole-Poland. The paper discusses the advantages of the use of these types of connectors in comparison to the classical approach of using the bolted joints as connectors between non-weldable materials in ships. We are emphasizing its eco-friendly effect on fuel consumption by lowering the weight of the whole structure. The thickness of the new prototype of the transition joint is lower than the standard thicknesses used by other manufacturers. The multilayer metallic composite was subjected to microstructural analysis. Factors influencing fatigue durability were analyzed and the basic analysis of fatigue cracks observed during tests was presented in form of crack propagation curves. The obtained fatigue results show that in most of the analyzed cases, the crack initiation is spotted in the heat-affected zone. According to the standard procedure of fatigue testing none of the prototype test specimens would fulfill the requirements set in the ABS standard used for the testing. This is crucial information in terms of the modification of the welding technology of the transition joint which has to be adapted. Nevertheless, the presented results show that there is a place for improvement in the used welding technology.

Influence of trace rare earth elements on very high cycle fatigue behavior of hot rolled bearing steel

In this study, the effect of trace rare earth (RE) elements on the fatigue property of bearing steel in very high cycle fatigue regime was investigated. For this purpose, ultrasonic tension–compression fatigue tests were conducted on specimens extracted from hot rolled bearing steels with and without RE addition. Crack propagation behavior within the characteristic “fish-eye” (FiE) area and the non-inclusion induced fatigue failure were analyzed after the fatigue test. Results showed that the addition of trace RE can modify inclusions to varying degrees. Further, it significantly reduces the volume fraction of inclusions as well as the number of large inclusions. Consequently, the fatigue life of bearing steel is more than doubled based on the 10% and 50% failure probabilities. During the propagation of cracks within the FiE area, the microstructure and intrinsic defects in bearing steel exhibit high sensitivity to the instantaneous driving force for crack propagation. The discontinuity in their size may result in abnormally slow crack propagation. For the non-inclusion induced fatigue failure of bearing steel, microcracks preferentially form at the junction of lath interfaces or at the enclosed area of martensite laths/plates which tend to grow along the interfaces perpendicular to the loading direction.

Criteria for determining the fatigue limit of Ni-based superalloy 718, considering the competition between opening- and shear-mode fatigue crack-growth

The mechanism that determines the fatigue limit associated with small-crack arrest in Ni-based superalloy 718 remains under debate. In order to comprehensively assess the alloy’s fatigue limit in relation to the growth threshold of a small fatigue crack, (i) a ΔKI-decreasing fatigue crack-growth test, (ii) torsional fatigue tests and (iii) tension-compression fatigue tests were conducted under fully-reversed loading conditions. In addition, elastic, crack-tip stress fields were analyzed for cracks under various loading conditions. Based on the results, a novel strategy for evaluating the alloy’s fatigue limit is proposed after consideration of two crack-arresting modes (i.e., opening and shear modes).

Fatigue life assessment of metal foils in multifunctional composites via combined experiments and simulations

In many applications metal foils are part of multifunctional composites exhibiting a wide range of (thermo-) mechanical fatigue loading. Data about low cycle fatigue of metallic foils subjected to tension-compression fatigue is sparse due to geometric limits. In this contribution, detailed information about design, tension-compression fatigue testing and data extraction of a layered sample are given. Fatigue failure of both copper and Pre-Preg are analysed using scanning electron microscopy and computed tomography. Numerical models are used to calculate the elastic and plastic strains for the copper foils within the composite sample, allowing a correlation to the observed fatigue life.

New neural network-based algorithm for predicting fatigue life of aluminum alloys in terms of machining parameters

Various classification of aluminum alloys is one of the most common applied materials in transportation industries due to the specific mechanical and material properties. Body of vehicles, including cars, ships, and airplanes, are constantly exposed to different cyclic loads that lead to surface damage and finally, fatigue failure occurs by crack growth. Therefore, the quality of the machined surface has a direct effect on the fatigue life of the products. In this regard, the most important source of surface roughness is the choice of machining parameters. To understand it, turning operations were performed on 2xxx and 7xxx series aluminum alloys considering different values of process parameters. For any series of aluminums, 189 high-cycle fatigue testing specimens were prepared, and experiments were performed by axial tension–compression fatigue test machine in 7 levels of stress (all tests were repeated three times and the mean failure cycles were reported as the fatigue life). Next, an Artificial Neural Network (ANN) based on the Back Propagation (BP) error algorithm was developed to predict fatigue life of Al alloys which are machined with different conditions. To this end, the parameters considered as input variables to the neural network structure include the Yield Strength (YS) and Ultimate Tensile Strength (UTS) to identify the aluminum series, as well as the process parameters such as cutting depth (d), rotational speed (R), and feed speed (V). In addition, the applied cyclic stress (S) to specimen was considered as input. Furthermore, surface roughness (Z) and number of cycles to failure (N) were considered as ANN output. The comparison of the obtained results from ANN predicting with the experimental values indicates that this approach was tuned finely. Eventually, the presented model can be a suitable alternative to perform fatigue tests with high costs and time-consuming.‌‌ Also, the most effective machining parameter on the surface roughness and fatigue limit was reported.

Application of Probabilistic Approach to Investigate Influence of Details in Time History of Temperature Changes on the HCF Life of Integrated Bridge Steel Piles Installed on Water

This research estimates the high-cycle fatigue (HCF) life of integrated concrete bridge installed on water due to temperature changes. To this end, CATIA software was used to geometrically model of a real-scale bridge. Next, thermal–structural coupling analysis was performed by finite element (FE) simulation in ANSYS WORKBENCH software. The comparison technique with experimental data was used to validate the simulation. Afterward, thermal analysis was performed due to air temperature changes in different modes, including the average monthly temperature changes (large variations) as well as the maximum and minimum monthly temperature changes (small variations). The results showed that the most changes in deck length and subsequent maximum deviation in the upper part of steel piles were related to the three warm seasons in the presence of the water. Eventually, a probabilistic approach was employed to find variable amplitude fatigue lifetime of the component based on the number of annual loading blocks. To achieve the high-accuracy response, the effective parameters of the proposed probabilistic approach, including order of Fourier series and the stress range, were optimized automatically. In addition, to obtain HCF behavior of raw material, axial tension–compression fatigue tests were performed on the standard specimens fabricated from steel piles. The results revealed that considering small variations in the calculation of structural fatigue life led to a 550% reduction in life compared to structural analysis due to large variations. In addition, the obtained results were compared with the finite element results.

The high-cycle fatigue behavior of carburized M50NiL steel with high-energy modification and compound infiltration: A comparative study

In this study, ultrasonic rolling (C + USRP) and plasma nitriding (C + N) is performed on the surface of M50NiL steel after carburizing， the tension-compression fatigue test of R = −1 on different samples. The results show that the maximum fatigue limit of C + N, C + USRP, and single carburizing are 770 MPa, 676 MPa, and 412 MPa, respectively. The residual stress relaxation in the fatigue process of C + N and C + USRP is tested and found that the initial residual compressive stress of C + N is lower than that of C + USRP, but its attenuation value is considerably smaller. The microscopic characterization of samples is conducted after the fatigue tests. The nanometer nitrogen compounds in the composite permeability layer showed a strong pinning effect, however, microplastic deformation limits the fatigue process. The C + N demonstrates a much lower residual compressive stress relaxation, consequently, the C + N short crack propagation effective driving force ΔKeff value decreases. As a result, due to the higher crack closure effect, the C + N fatigue limit is observed higher than the C + USRP.

Directions of high cycle fatigue cracks emanating from circular notches studied by optical profilometry

Current models for predicting the fatigue endurance of notched solids use the stresses along a straight line, beginning at the notch root, as a simplification of the real crack propagation path. In this work, the experimental crack paths for hollow notched samples were analysed through different microscopy techniques, with the objective of establishing high cycle fatigue crack growth directions in a mild steel. Fully reversed tension–compression fatigue tests (R=−1) of thin-walled tube specimens with a passing-through hole were carried out. The crack paths observed in the outer cylindrical surface were studied in each case, with special attention to the crack initiation point and the crack direction along the first grains. Moreover, the analysis of the fracture surfaces allowed the same analysis to be performed to determine the internal crack paths. It was observed that the crack initiation point was close to the maximum principal stress point at the hole contour as obtained from linear elastic finite element analysis, and the crack direction in its initiation was generally close to Mode I direction, contrary to the conventionally accepted 45∘ crack growth direction.

High-cycle fatigue strength prediction of ductile Ni-resist cast iron containing casting defects

Ductile Ni-resist cast iron with an austenitic matrix structure contains significant casting defects that reduce the fatigue strength. Using specimens with artificial defects of various shapes and sizes, rotating bending and tension–compression fatigue tests were carried out. The maximum-sized defect in a specimen determined the fatigue limit. Therefore, the lower bound of the scatter in the fatigue limit was estimated using the area parameter model in combination with the statistics of extreme values applied to the maximum defect sizes. In contrast, the competition between propagation of multiple cracks from small material defects controlled the fatigue life.

Cryogenic Accelerated Fatigue Tester for additive manufactured polymer composite mechanical property measurement

Additive manufacturing (AM) of polymer matrix composite (PMC) materials maintains the potential to significantly reduce part count, weight, and costs for future aerospace development. However, a lack of maturity in loading systems has inhibited the characterization of these materials for the cryogenic environment of space. These PMCs demand lifespan endurance when faced with cryogenic thermal cycling in series with high-frequency mechanical loading. Few mechanical testers have been capable of achieving the cryogenic temperatures and actuating frequency to simulate the environment that a PMC endures in a cryogenic application. Also, these testers have yet to define the tensile and fatigue PMC mechanical behavior at these temperatures. To curate a cryogenic, fatigue profile on PMCs, the Cryogenic Accelerated Fatigue Tester (CRAFT) was developed. CRAFT utilizes a 12-kN load frame in unison with a cryocooler to perform tension-tension and tension-compression fatigue tests up to 100 Hz in a liquid hydrogen environment. This publication reviews the CRAFT design and capabilities. Determining the cryogenic fatigue life of 3D-printed PMCs through testing in CRAFT allows for the validation of proper material implementation and the future optimization of these materials in cryogenic environments.

Stress Evaluation of Welded Joints with Metal Magnetic Memory Testing Based on Tension-Compression Fatigue Test.

Metal magnetic memory testing (MMMT) is an effective nondestructive technique for fatigue damage monitoring of weldments because of its capacity for stress evaluation. An experimental investigation of the effect of the applied fatigue stress on MMMT signals, including the tangential component Bx and the normal component Bz, during tension–compression fatigue tests in welded joints was carried out systematically. The Bx and Bz signals at different fatigue cycles and fatigue stresses were collected and analyzed, and the results showed that there was a peak of Bx and abnormal peaks of Bz that existed at the welded joint before loading. After loading, the peak of Bx and the abnormal peaks of Bz reversed, and the Bx signals moved upward and the Bz signals rotated anticlockwise dramatically in the first few fatigue cycles. After the fatigue cycle number was larger than 1000, Bx and Bz were stable, with very little fluctuation. In addition, the characteristics of Bx signals, the mean value, and the peak value of the average of Bx had an extremely significant linear relationship with the applied fatigue stress during the stable stage of the fatigue test, which indicates that MMMT is a feasible method for fatigue stress evaluation and even residual fatigue life estimation for weldments in service.

Damage evolution in cross-ply laminates under tension–compression and compression-compression cyclic loads

Tension-Compression and Compression-Compression fatigue tests were carried out on glass/epoxy cross-ply laminates, with different values of the minimum to maximum load ratio R (−1, −3, −5, −7, −10 and 20). During the tests, the damage evolution in the 90° ply was monitored at the macro-and micro-scales. Three damage scenarios were observed, depending on the load ratio: i) initiation and propagation of transverse cracks for R ≥ −3, ii) initiation of multiple inclined short cracks for R = 20, iii) a mixed damage type with the presence of both transverse cracks and inclined short cracks for −10 ≤ R ≤ −5. Finite Element analyses of micro-scale Representative Volume Elements, combined with a recently developed crack initiation criterion, revealed the role of the Local Hydrostatic Stress in the matrix in controlling the different damage scenarios. Eventually, quantitative analyses showed a highly detrimental effect of the compressive part of the cycle on the transverse crack initiation and propagation.

Multi-Fractal Scaling Law applied to VHCF with an emphasis on statistical fluctuations

In recent decades, ultrasonic testing machines have allowed to investigate the very-high cycle fatigue (VHCF) range, featuring feasible gigacycle fatigue testing in a very short time, although the influence of frequency is still partly controversial. The fatigue behaviour depends on the random distribution of initial defects, whatever the stress range amplitude is. As a consequence, the structural size comes into play and the so called ”size-effects” are usually observed. On the other hand, the scaling is not uniform when sufficiently large dimensional ranges are analysed. To this aim, the multi-fractal formalism was adopted to explain the observed specimen-size effect in the VHCF regime when a wide dimensional range is investigated. In addition, the statistical dispersion of experimental results was accounted by adopting different probabilistic functions. Among them, the Generalized Extreme Value Distribution Type-I was selected. In this way, it was possible to derive the analytical relationship for probabilistic-scale dependent P-S-N-b curves.Subsequently, the proposed model was used to analyse the experimental data obtained in an experimental campaign carried out at Politecnico di Torino by the present authors. More in detail, ultrasonic fully reversed tension–compression fatigue tests in the very-high cycle fatigue (VHCF) range were conducted on a set of hourglass and dog-bone specimens made of EN AW-6082 aluminium alloy, with a diameter in the middle cross-section ranging from 3 mm up to 30 mm.The comparison between the theoretichal model and the experimental data allowed to demonstrate the ability of Multi-Fractal Scaling Law (MFSL) to provide objective values of the fatigue strength of full-size components subjected to VHCF and to guarantee safe structural design.

Influence of aggregates properties on microstructural properties and mechanical performance of asphalt mixtures

Asphalt mixtures can perform suitably in road and airfield pavements. However, with rapid increases in traffic volumes, harsh climate environments, and heavier loads, there is an increased interest in improving the mechanical properties of asphalt materials through a suitable design of the microstructure of the asphalt mixture. Aggregates’ physical and chemical properties significantly influence the interface interaction between aggregates and binders and achieve strong, durable and cost-effective asphalt mixtures. This study prepared the asphalt mixtures from three different aggregate sources, i.e. Granite 1 (GD 1), Granite 2 (GD 2) and limestone (GD 3) and captured the microstructural properties using a charge-coupled device (CCD) digital camera and analysed them by iPAS software. The effect of the daily temperature variation of the environment to the corresponding temperature gradient through the depth of all asphalt mixtures layers was assessed. The results indicate that sodium oxide (Na2O) + potassium oxide (K2O) + calcium oxide (CaO) + silicon (SiO2) has a significant influence on the electrical conductivity of granite samples at high temperatures and pressure. Marshall, wheel tracking, three-point bending beam, double tension–compression fatigue tests at two periods were conducted to investigate any relationship between the structural performance of the asphalt mixtures and their microstructural properties. Additionally, the normal contact fabric tensor (F) was developed to t evaluate the interlocking of aggregates in asphalt mixtures, and the correlation with the mechanical performance was performed. The results show that the higher amount of silicon and aluminium in aggregates, the better the aggregate texture and the high contact points weight. In addition, high contact points weight has a notable impact on the Marshall stability, rutting depth, dynamic stability, stiffness modulus and complex Poisson’s ratio at high and low temperatures. All samples showed good mechanical performance at all temperatures because of their high aggregate particles F.

Consequences of Deep Rolling at Elevated Temperature on Near-Surface and Fatigue Properties of High-Manganese TWIP Steel X40MnCrAl19-2

Due to pronounced work-hardening induced by the complex interplay of deformation mechanisms such as dislocation slip, twinning and/or martensitic phase transformation, high-manganese steels represent a class of materials well-suited for mechanical surface treatment. In the present study, the fatigue behavior of a high-mangsanese steel showing twinning-induced plasticity (TWIP) effect at room temperature (RT) was investigated after deep rolling at 550 °C. Results are compared to a former study discussing the behavior after RT deep rolling. Evolution of the near-surface microstructure was analyzed by scanning electron microscopy (SEM), microhardness measurements and residual stress depth profiles obtained by X-ray diffraction (XRD). Both uniaxial tensile tests and uniaxial tension-compression fatigue tests have been conducted in order to rationalize the macroscopic material behavior. Following deep rolling at 550 °C, SEM measurements employing electron backscatter diffraction (EBSD) revealed a heavily deformed surface layer as well as localized deformation twinning. Specimens showed inferior hardness and residual stress depth profiles when compared to RT deep rolled counterparts. Tensile tests indicated no difference between the conditions considered. Fatigue properties however were improved. Such behavior is rationalized by a more stable residual stress state induced by dynamic strain aging.

Unforeseen, negative interaction-effect of adjacent circumferential notches on the fatigue limit of Ni-based superalloy 718

Investigations were conducted on the interaction-effects of adjacent, circumferential V-notches on the fatigue limit of Alloy 718, with the aid of fully-reversed, tension–compression fatigue tests. Contrary to expectation, specimen with seven adjacent circumferential notches had lower fatigue limit than that with a single circumferential notch. This phenomenon was attributed to the increased stress intensity factor (SIF) range of shear-mode fatigue cracks at notch-roots, resulting from competition between two factors: (i) stress mitigation through the mechanistic interaction of notches (decreased SIF) and (ii) the orderly, spatial alignment of crack-planes, due to the asymmetric stress-fields in the vicinity of notch-roots (increased SIF).

Influence of Shot Peening on the Isothermal Fatigue Behavior of the Gamma Titanium Aluminide Ti-48Al-2Cr-2Nb at 750 °C

One possibility to improve the fatigue life and strength of metallic materials is shot peening. However, at elevated temperatures, the induced residual stresses may relax. To investigate the influence of shot peening on high-temperature fatigue behavior, isothermal fatigue tests were conducted on shot-peened and untreated samples of gamma TiAl 48-2-2 at 750 °C in air. The shot-peened material was characterized using EBSD, microhardness, and residual stress analyses. Shot peening leads to a significant increase in surface hardness and high compressive residual stresses near the surface. Both effects may have a positive influence on lifetime. However, it also leads to surface notches and tensile residual stresses in the bulk material with a negative impact on cyclic lifetime. During fully reversed uniaxial tension-compression fatigue tests (R = −1) at a stress amplitude of 260 MPa, the positive effects dominate, and the fatigue lifetime increases. At a lower stress amplitude of 230 MPa, the negative effect of internal tensile residual stresses dominates, and the lifetime decreases. Shot peening leads to a transition from surface to volume crack initiation if the surface is not damaged by the shots.