Cyclic Tensile Research Articles

Influence of build orientation and heat treatment on high cycle fatigue of additively manufactured AlSi10Mg

This study examines how build orientation and heat treatment affect microstructure and, consequently, the mechanical properties in tensile and high cycle fatigue of additively manufactured AlSi10Mg. Specimens were manufactured in two orientations (0° and 45°) using a laser-based powder bed fusion and subsequently subjected to two heat treatments: (i) direct aging at 170 °C for 2 h (A170) and (ii) stress relief at 300 °C for 2 h (SR300). Two routes for direct aging were previously explored to determine the ideal time and temperature for heat treatment: direct aging at 155 °C and direct aging at 170 °C, both for up to 10 h. It was found that aging at 170 °C for 2 h resulted in higher hardness, yield strength, and ultimate tensile strength than aging at 155 °C for 6 h (A155). The specimens subjected to heat treatment A170 exhibited similar stress amplitude at 106 fatigue life than SR300, with 43.8 MPa and 45.6 MPa, respectively. At similar stress amplitudes, below 106 cycles, the build orientation (0° and 45°) slightly affect the high cycle fatigue properties.

A reduced graphene oxide-coated conductive surgical silk suture targeting microresistance sensing changes for wound healing

Conventional sutures used in surgical procedures often lack the capability to effectively monitor physical and chemical activities or the microbial environment of surgical wounds due to their inadequate mechanical properties, insufficient electrical accuracy and unstability. Here, we present a straightforward layer-by-layer coating technique that utilizes 3-glycidoxypropyltrimethoxysilane (CA), graphene oxide (GO), and ascorbic acid (AA) to develop conductive silk-based surgical sutures (CA-rGSFS). The CA-rGSFS feature a continuous reduced graphene oxide (rGO) film on their surface, forming robust hydrogen bonds with silk fibroin. The reduction process of rGO is confirmed through Raman analysis, demonstrating an enhanced D peak to G peak ratio. Notably, the CA-rGSFS exhibit exceptional mechanical properties and efficient electron transmission, with a knot-pull tensile strength of 2089.72 ± 1.20 cN and an electrical conductivity of 130.30 ± 11.34 S/m, respectively, meeting the requirements specified by the United States Pharmacopeia (USP) for 2-0 sutures. These novel CA-rGSFS demonstrate the ability to accurately track resistance changes in various fluid environments with rapid response, including saline, intestinal, and gastric fluids. The suture also retains remarkable stretchablility and stability even after enduring 3000 tensile cycles, highlighting their potential for precise surgical site monitoring during the wound healing process.

A Preisach Model Defining Correlation between Monotonic and Cyclic Response of Structural Mild Steel

This article delivers a new Preisach model representing the correlation between the elastoplastic behavior of structural mild steel under axial monotonic and cyclic loading with damage. The newly formed model is based on the experimentally defined correlation between axial monotonic and cyclic behavior of structural mild steel. To examine the monotonic and cyclic behavior of structural mild steel and find fitting material properties for the model, monotonic and cyclic axial tensile tests are performed. Tests are executed on coupons of the commonly used European structural steel S275. The model represents a mathematical description of modified single-crystal material behavior under monotonic loading. Two different approaches were used to describe damage in the multilinear mechanical model. The excellent agreement with experimental results is achieved by infinitely linking many single-crystal elements in parallel, forming the polycrystalline model. This model provides a good solution for everyday engineering practice due to its geometric representation in the form of the Preisach triangle and the lower costs of monotonic tests used to define material properties compared to cyclic tests.

Bio-Templated Aerogel Fibers: Heterogeneous Spinodal Architecting and In Situ Fibrillation of Thermoplastic Polyurethane-Silica on Nanostructured Cellulose Nanofiber Scaffold for Enhanced Thermomechanical Performance.

This study addresses the inherent fragility and fractal limitations of traditional silica aerogels by developing a bio-templated aerogel fiber. Integrating cellulose nanofibers (CNFs), thermoplastic polyurethane (TPU), and silica aerogel (SA) in a dimethyl sulfoxide (DMSO) dispersion, a gel-spinning technique was employed to create aerogel fibers with superior thermomechanical performance. CNF also provided excellent rheological modification for successful spinnability, fast gelation, and fiber formation. The unique hierarchical structure of these fibers, formed through hot-stretching and surface modification, combined the superior mechanical strength and flexibility of TPU with the exceptional insulation properties of CNF and SA. The CNF network, encapsulated within the SA particles, formed a core-shell structure, axially aligned, that significantly enhances the thermal stability and mechanical performance of the fibers while maintaining a lightweight and porous architecture. Comprehensive morphological, thermal, and mechanical analyses were conducted to evaluate the properties of the developed aerogel fibers. Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy verified the successful surface modification and grafting reactions on CNF, contributing to improved hydrophobicity and thermal insulation. Adjusting the CNF content allowed for tailoring of the thermomechanical characteristics, with a notable 294% increase in tensile strength from 5.3 to 15.6 MPa and an enhanced crystallization temperature from 106 to 119.97 °C. Furthermore, cyclic tensile and compression tests validated the durability and shape recovery capabilities of the aerogel fibers, making them promising candidates for high-performance applications in extreme environments. The thermal conductivity validated by experimental data further highlights the potential of CNF-based aerogel fibers as sustainable and multifunctional materials for advanced thermal insulation, mechanical reinforcement, and flexible structural applications.

Fatigue life modeling for a low alloy steel after long-term thermal aging

Fatigue failure of materials has a considerable impact on the safety of equipment in service. In this study, axially tensile and low cycle fatigue tests were conducted on a low alloy steel after accelerated thermal aged at 450 °C for 10,000 h. The experimental results indicate that the ultimate and yield strengths increase moderately, while the fatigue life of specimens experience a slight decrease in this circumstance. The fracture analysis demonstrates that the bainite breaking facilitates the fatigue crack initiation and propagation after thermal aging, which is accompanied by a decrease in plastic strain amplitude. Therefore, the plastic strain amplitude is considered as an indicator of thermal aging in fatigue life modeling for the low alloy steel. Finally, a novel life model that incorporates both aging time and temperature was proposed for rapid prediction of low cycle fatigue life. It is assumed that this model promotes reliable fatigue life prediction in low alloy steels under various thermal aging circumstances, as well as the extrapolation of fatigue performance of the material in service.

Tensile and High Cycle Fatigue Behavior of 316L and Fe-18Cr-22Mn-0.65N Stainless Steel at Stress Ratio of 0.1 at Room Temperature

Tensile and High Cycle Fatigue Behavior of 316L and Fe-18Cr-22Mn-0.65N Stainless Steel at Stress Ratio of 0.1 at Room Temperature

Controlled Fabrication of Wafer-Scale, Flexible Ag-TiO2 Nanoparticle-Film Hybrid Surface-Enhanced Raman Scattering Substrates for Sub-Micrometer Plastics Detection.

As an important trace molecular detection technique, surface-enhanced Raman scattering (SERS) has been extensively investigated, while the realization of simple, low-cost, and controllable fabrication of wafer-scale, flexible SERS-active substrates remains challenging. Here, we report a facile, low-cost strategy for fabricating wafer-scale SERS substrates based on Ag-TiO2 nanoparticle-film hybrids by combining dip-coating and UV light array photo-deposition. The results show that a centimeter-scale Ag nanoparticle (AgNP) film (~20 cm × 20 cm) could be uniformly photo-deposited on both non-flexible and flexible TiO2 substrates, with a relative standard deviation in particle size of only 5.63%. The large-scale AgNP/TiO2 hybrids working as SERS substrates show high sensitivity and good uniformity at both the micron and wafer levels, as evidenced by scanning electron microscopy and Raman measurements. In situ bending and tensile experiments demonstrate that the as-prepared flexible AgNP/TiO2 SERS substrate is mechanically robust, exhibiting stable SERS activity even in a large bending state as well as after more than 200 tensile cycles. Moreover, the flexible AgNP/TiO2 SERS substrates show excellent performance in detecting sub-micrometer-sized plastics (≤1 μm) and low-concentration organic pollutants on complex surfaces. Overall, this study provides a simple path toward wafer-scale, flexible SERS substrate fabrication, which is a big step for practical applications of the SERS technique.

Structural health monitoring of scarf bonded repaired glass/epoxy laminates interleaved with carbon non-woven veil

Bonded repair patches/joints often introduce vulnerabilities in composite laminates, making them prime candidates for structural health monitoring (SHM). In this study, stepped-scarf bonded joints were manufactured using glass fibre-reinforced epoxy laminates as representative repair patches, and a novel SHM approach through the electrical resistance change method was applied. To establish an electrically conductive path within the stepped-scarf joint, non-woven carbon fibre veils with areal weights of 10 g/m² and 20 g/m² were interlaid along the stepped bondline. Two types of tensile tests were performed. In the first set of tests, the stepped-scarf joints underwent monotonic quasi-static tensile loading until the bondline was completely fractured (catastrophic failure) and the change in electrical resistance was continuously monitored. The failure stress of the joint with a 10 g/ m² carbon veil was only marginally decreased (∼2 %) in comparison with that of the joints without a carbon veil, while the failure stress of the joint with a 20 g/m² carbon non-woven veil was considerably decreased (by ∼9 %). However, the joints with 10 g/m² and 20 g/m² carbon veils exhibited a significant change in electrical resistance (∼200 % and ∼1000 %, up to full failure, respectively). Simultaneously, the change in electrical resistance was used for the detection of damage initiation and progression, supported by digital images taken during the tests. In the second set of tests, the joints were subjected to a cyclic tensile loading/unloading regime and the change in electrical resistance was monitored. A significant amount of permanent change in resistance during the unloading phases (up to 120 % in the bondline with a 20 g/m² veil) was observed, providing insights into the laminate and bondline damage evolution. In addition, thermal images obtained with the joule heating method in the cyclic tensile tests were used to confirm the damage detected with the electrical resistance change method. Moreover, the micrographs from the fracture surfaces indicated that the variations in electrical resistance change are largely caused by damage occurring within or near the carbon veils. In conclusion, the results demonstrate that the presented SHM approach, which incorporates carbon non-woven fibre veils within non-conductive laminate composites, holds promise for monitoring damage initiation and propagation in repaired composite laminates as well as adhesively bonded composite laminate joints, without adversely influencing the structural integrity of the bondline.

Flexible AgNW/PDMS nanocomposite for strain and pressure sensing

This study presents the fabrication and characterization of an ultra-thin (<1 mm) piezoresistive sensor based on a silver nanowire (AgNW) and polydimethylsiloxane (PDMS) nanocomposite, capable of simultaneous strain and pressure sensing. The sensor exhibits high sensitivity, detecting strains as low as 0.5 % with a range of up to 40 %, demonstrates frequency responsiveness from 0.5 to 3 Hz, and maintains functionality over 1000 cycles. The sensor’s performance was evaluated through cyclic tensile and compressive tests. We hypothesize that the compression sensing mechanism is a consequence of the Poisson effect in the PDMS substrate, where transverse compression induces axial strains parallel to the AgNW network, causing disconnections within the nanowire matrix. The sensor’s versatility was demonstrated through various biofeedback applications, including finger bending, applied pressure, calf raises, and elbow flexion. With its thin profile and dual-mode sensing capability, this AgNW/PDMS nanocomposite sensor shows promise for biomechanics, sports science, and healthcare monitoring applications.

Thermo-mechanical fatigue analysis of ferritic stainless steel STS444LM for exhaust manifold application

This work presents thermo-mechanical fatigue (TMF) life analysis of ferritic stainless steel STS444LM recently developed to enhance the durability of the automotive exhaust manifolds. To determine cyclic material properties, isothermal tensile and low cycle fatigue (LCF) tests at temperature ranging from 200 °C to 900 °C under two different strain rates of 0.1 %/s and 0.01 %/s are performed. Based on these tests, the unified Chaboche visco-plasticity model is determined. Then, the TMF test using the V-shaped specimen subjected to the temperature cycle from 250 to 850 – 950 °C with three different dwell times at the maximum temperature is performed. An energy-based model based on the Morrow model is determined using TMF test data by incorporating effects of the dwelling time and maximum temperature.

Crack Growth Patterns of Aluminum Tubular Specimens Subjected to Cyclic Tensile Loads

This study presents a detailed analysis of a fatigue test campaign in order to identify different crack patterns. It was conducted on 6061-T6 aluminum tubular specimens featuring an internal diameter of 10 mm and different thicknesses (2, 3 and 4 mm). These specimens were subjected to cyclic tensile loads with a load ratio of R = 0.1, utilizing a sinusoidal load function at a frequency of 3 Hz. The investigation examines the crack growth rates, the stress intensity factor, and the final and intermediate fracture zones by applying overloads in some cases. The differences with two-dimensional specimens and the importance of this study for the interpretation of results with biaxial loading states are highlighted. The different states of crack growth detected are analyzed using artificial vision techniques. The differences between the exterior and interior faces of the specimen are revealed, and a series of states prior to the formation of the radial crack front expected in these specimens are identified.

Experimental Investigation of the Impact of Loading Conditions on the Change in Thin NiTi Wire Resistance during Cyclic Stretching.

This paper presents the results of an experimental study designed to evaluate the effect of repeated stretching cycles on the electrical resistance change in a NiTi alloy wire. In particular, tests were carried out to determine the effect of the type of loading on resistance change in the investigated wires. Wires with a diameter of 100 μm were used in the research. The experiment was carried out on a dedicated test stand designed for this purpose. During the test, the samples were subjected to 40 identical tensile cycles. The electrical resistance, sample elongation, and tensile force during successive stretching cycles were measured. The conducted research demonstrated the impact of elongation and reorientation of the structure on the resistance change in NiTi alloy thin wires. The research included a comparison of the effect of two different types of loading on the electrical resistance change in the sample. During cyclic stretching of a NiTi alloy sample with constant displacement, a decrease in electrical resistance was observed after each successive stretching cycle. Alternatively, when stretching with a constant force, the value of electrical resistance increased. In both types of loads, the greatest change in resistance value was observed at the initial cycles.

Microwave Radiation Assisted Construction of Fused Deposition Modeling 3D Printing Flexible Sensors

AbstractWith the rapid development of the internet of things, the simple preparation of sensors has become a challenge. The present work presents the simple preparation of flexible sensors by using the fused deposition modeling (FDM) 3D printing combined with the microwave radiation‐assisted treatment of the thermoplastic polyurethane (TPU) with carbon nanotubes (CNTs) as conductive fillers to create the flexible sensors. The as‐prepared TPU/CNT composites exhibit the 7.27 MPa tensile strength and 401% elongation at break, similar to those of the pure TPU. After 200 tensile cycles, the TPU/CNT composites can still stably convert pressure into electrical signals, which can be used as flexible sensors with high sensitivity (0.879 kPa−1). In addition, shoe insoles and finger cover with sensing performance are fabricated through the FDM 3D printing technology, demonstrating the potential of the sensors to monitor human gait, finger straightening, and bending movements. The as‐proposed method involves the embedding CNTs as conductive fillers on the surface of TPU to form the TPU/CNT composite conductive layers on the surface of TPU, which is beneficial for maintaining the elasticity of the polymer matrix. The challenges in preparing stable, low‐cost, and scalable flexible sensors and highlights of the advantages of 3D printing technology in manufacturing flexible piezoresistive sensors are also deeply discussed.

Comprehensive Study of Mechanical, Electrical and Biological Properties of Conductive Polymer Composites for Medical Applications through Additive Manufacturing.

Conductive polymer composites are commonly present in flexible electrodes for neural interfaces, implantable sensors, and aerospace applications. Fused filament fabrication (FFF) is a widely used additive manufacturing technology, where conductive filaments frequently contain carbon-based fillers. In this study, the static and dynamic mechanical properties and the electrical properties (resistance, signal transmission, resistance measurements during cyclic tensile, bending and temperature tests) were investigated for polylactic acid (PLA)-based, acrylonitrile butadiene styrene (ABS)-based, thermoplastic polyurethane (TPU)-based, and polyamide (PA)-based conductive filaments with carbon-based additives. Scanning electron microscopy (SEM) was implemented to evaluate the results. Cytotoxicity measurements were performed. The conductive ABS specimens have a high gauge factor between 0.2% and 1.0% strain. All tested materials, except the PA-based conductive composite, are suitable for low-voltage applications such as 3D-printed EEG and EMG sensors. ABS-based and TPU-based conductive composites are promising raw materials suitable for temperature measuring and medical applications.

Piezoelectricity in NbOI2 for piezotronics and nanogenerators

2-dimensional (2D) piezoelectric materials have gained significant attention due to their potential applications in flexible energy harvesting and storage devices. Recently, niobium oxide dihalides NbOI2 stands out as a multifunctional anisotropic semiconductor family with an exceptionally high lateral piezoelectric constant (~21.8 pm/V), making it a promising candidate for energy conversion applications. Here we report the experimental observation of anisotropic in-plane piezoelectricity in multilayer NbOI2. Current-voltage relationships reveal a significant piezotronic effect in two typical crystalline orientations. Additionally, cyclic tensile and release experiments demonstrate an intrinsic current output of up to 140 pA when subjected to a tensile strain of 0.51%. A flexible piezoelectric nanogenerator prototype is demonstrated on the human finger and wrist, which opens up new avenues for the development of wearable electronic devices and provides valuable insights for further exploration in this field.

Study on surface integrity and fatigue performance of FeCoCrNiAl₀.₆ high-entropy alloy based on thermo-mechanical coordinated control

This study investigates the effects of various lubrication techniques on the surface integrity and fatigue life of FeCoCrNiAl0.6 high-entropy alloy during machining. By combining cutting experiments, fatigue tensile tests, and Abaqus/Fe-safe simulations, the research offers a comparative analysis of surface morphology, roughness, and fatigue life across different lubrication scenarios.The findings show a marked improvement in surface quality as cutting speed increases under all lubrication conditions. However, increased cutting depth generally leads to a decline in surface flatness. Specifically, surface roughness decreases with higher cutting speeds. For example, at 1200 m/min in dry cutting, the surface roughness is around 0.77 μm, which drops to 0.40 μm at 3000 m/min, representing a 48 % reduction. Under cryogenic minimum quantity lubrication (CMQL) at 1200 m/min, the roughness is 0.49 μm, decreasing to 0.25 μm at higher speeds, reflecting a 48.9 % reduction.However, increased cutting depth significantly deteriorates surface quality, with a notable rise in surface roughness values. Among the tested lubrication techniques, surface quality ranks as follows: CMQL > MQL > Dry.Regarding fatigue life, higher cutting speeds substantially enhance tensile cycle counts under all lubrication conditions. Specimens under CMQL achieved 2,000,042 cycles, compared to 1,238,520 cycles with minimum quantity lubrication (MQL) and 702,245 cycles in dry cutting—equating to 61.9 % and 35.1 % of the tensile cycle count for CMQL, respectively.Fatigue life decreases with greater cutting depth. For example, compared to a 0.2 mm cutting depth, tensile fatigue cycles decrease by 87.9 % for CMQL, 86 % for MQL, and 91.8 % for dry cutting at a depth of 0.5 mm.

Development and engineering application of fiber bragg grating intelligent cable in large-span hyperbolic parabolic spatial cable network

In order to accurately control the prestress force of cables in long-span cable net structures, a new type of fiber Bragg grating (FBG) intelligent cable was developed. The FBG sensor was directly encapsulated inside the cable, and the sensing performance of the intelligent cable was verified by the cyclic tensile tests. The results show that the sensitivity coefficients of FBG monitoring are basically consistent, and the linearity deviation of the fiber Bragg grating is less than 4.67 %. Based on a real project Shunde Desheng Sports Center, a 114 m long-span saddle-shaped cable net structure model was established using finite element analysis, and the distribution and correlation of internal forces of cables in different tension stages were calculated and compared with the actual monitoring results of intelligent cables. The analysis results indicate that the force changes of intelligent cables is basically consistent with the value of finite element simulation. According to the data of long-term intelligent cable monitoring, the change of cable force caused by the temperature deformation of the steel ring beam is much greater than the influence of the temperature rise and fall of the cable itself on the cable force. Intelligent cables can provide a reference for cable force monitoring of long-span cable net structures.

Simulating loading–unloading hysteretic behaviors of nematic-genesis polydomain nematic elastomers

Nematic elastomers (NEs) are lightly cross-linked elastomers with nematic mesogens integrated in their polymer networks. Combination of large deformation capability with nematic-isotropic phase transition enables NEs to be the most promising soft materials for impact attenuation, actuation and soft robotics. In this paper, we focus on nematic-genesis polydomain NEs (N-PNEs) where mesogens are cross-linked at nematic states. N-PNEs are capable of absorbing and dissipating energy and easy to synthesize. We present a Voronoi diagram-based finite element model for specimen-scale N-PNEs, and investigate the cyclic tensile and compressive behaviors of N-PNEs at different strain rates. Our simulations reveal a smooth polydomain-monodomain transition during loading, accompanied by a full recovery of polydomain texture after the load is removed, indicating a memory effect of initial disordered mesogen alignment. The predicted behaviors align well with experimental observations, which validates our model. Furthermore, we assess the energy absorption and dissipation capabilities of N-PNEs compared to monodomain NEs, identifying conditions where N-PNEs exhibit superior performance. This study not only enhances our understanding of polydomain-monodomain transitions in N-PNEs, but also lays the groundwork for the development of N-PNE-based energy absorbers.

Fatigue resistant photo-responsive [c2] daisy chain Poly(rotaxane) hydrogel

A photo-responsive poly(rotaxane) hydrogel based on [c2] daisy chain was synthesized. The supramolecular hydrogel was robust with the compression stress of 3136 kPa at the strain of 90 %, the tensile strength of 297 kPa and the elongation at break of 694 %. At the same time, the gel film showed fast photoresponsive behavior even in dry state, showing 15o bending angle under 2 s 365 nm UV irradiation. Besides, the hydrogel exhibited good fatigue resistance. Its recovery ratio remains higher than 80 % during multiple cyclic tensile and compression test, making it an alternative and promising platform for photo-responsive materials with emergent mechanical performances and attractive fatigue resistance.

Comparative study on tensile and high cycle fatigue behaviour of 316L(N) SS hardfaced with Ni-Cr-B-Si alloy by GTA and laser cladding processes

In sodium-cooled fast reactors (SFR), 316L(N) SS grid plate is hardfaced with Ni-Cr-B-Si alloy to achieve higher wear resistance. Tensile and fatigue forces are acting at the interface between substrate and deposit due to different thermal expansion coefficients of those two materials, which can cause cracking of deposit and fracture during operation. Thus, it is very important to consider appropriate hardfacing method which can provide higher tensile and fatigue strength to avoid cracking/debonding at the interface. To find a solution to this problem, two hardfacing techniques, namely Gas Tungsten Arc (GTA) and Laser cladding (LC), are taken into consideration. Hardfaced specimens are prepared using each process on which tensile and high cycle fatigue tests are conducted. From the experimental testing, stress-strain and S-N curves are generated to predict the tensile and fatigue behaviour of specimens. Fractographic studies are conducted at fractured surfaces to understand the fatigue crack nucleation and propagation characteristics. The experimental results for both processes are compared. Tensile and fatigue strength of LC specimens are ∼11 % and ∼17 % less than those of GTA specimens due to its higher brittleness. Thus, GTA process is recommended as the efficient hardfacing process for grid plate of SFR.