Improved Fatigue Resistance Research Articles

Functionalizing MXene towards highly stretchable, ultratough, fatigue- and fire-resistant polymer nanocomposites

Thermoplastic polyurethane (TPU) features many important industrial applications, but intrinsic flammability extremely impedes its practical applications. Current fire-retardant strategies often lead to improved flame retardancy but reduced mechanical properties (strength, ductility, and toughness). Hence, to date it has been unsuccessful to design advanced TPU materials that are strong, stretchable, tough, fatigue-and fire-resistant to meet increasing performance portfolio requirements. Here, we report a hybridized fire retardant (Zr-MXene) by in situ facilely loading zirconium amino-tris-(methylenephosphonate) (Zr-AMP) onto the titanium carbide (MXene) surface. Our results show that with 1 wt% of Zr-MXene, the resultant TPU nanocomposites demonstrate a record break strain (2060%) and toughness (316 MJ/m3) to date, in addition to increased tensile strength by 43.4% and improved fatigue resistance relative to the TPU matrix, because of favorable interfacial hydrogen-bonding. Moreover, the resultant TPU material exhibit significantly reduced flammability as a result of the combined physical barrier, catalytical carbonization and diluting effects of Zr-MXene. This work provides a promising strategy for the creation of multifunctional MXene and its polymeric nanocomposites, which hold great promise for many industrial applications.

Characterization of Fatigue Resistance of Warm Mix Binders Using Linear Amplitude Sweep Test

Fatigue failure in asphalt pavements occur due to the accumulation of damage under repeated traffic loading. Fatigue cracks generally occur within the binder phase of the asphalt mixture. Hence the specifications for properties related to fatigue resistance of asphalt binder become an important screening tool to select binders that are not inherently susceptible to fatigue under given environmental and traffic conditions. The Current Superpave Performance Grading (PG) specifications use parameter |G*|.·sinδ of asphalt binder to assess the fatigue susceptibility of asphalt mixes. These specifications do not accurately characterize the fatigue resistance of asphalt binders because |G*|.·sinδ is determined by applying a cyclic loading in the Dynamic Shear Rheometer (DSR) at a very small strain amplitude (1%). In this study, Linear Amplitude Sweep (LAS) test was considered to characterize the fatigue resistance of asphalt binders with warm mix additives. Warm mix asphalt (WMA) is a developing technology that can allow asphalt concrete to be produced at lower temperatures. This paper presents result of a study carried out to investigate the fatigue characteristics of warm-mix asphalt binders using a linear amplitude sweep test. Three warm-mix additives; Sasobit®, Evotherm™ and Rediset® are considered. Viscosity grade (VG 30), Polymer modified binder (PMB 40) and Crumb rubber modified binder (CRMB 60) were selected as base binders for this investigation. Physical and rheological tests were carried out for the characterization of these binders. The LAS test was carried out at 25 °C in a DSR, and the fatigue parameters were calculated from stress–strain plots. Test results showed that the changing trend in fatigue life of mixes is more related to the fatigue parameter Nf from LAS test than to |G*|. sinδ values of the binders. It was also observed that most of the warm mix binders have improved fatigue resistance at 25 °C in comparison to the control binders. The effect of Rediset® additive was found to be insignificant in the case of VG 30 grade binder only.

Damage Identification on Impact and Lightning Damage of Flax Composite Laminates (Linum usitatissimum) Using Long-Pulse Thermography of a Low-Resolution Infrared Camera

The demand for composite fiber material is significantly high due to its excellent mechanical properties and its use in various industries. Recently, with the increasing awareness of environmental issues, researchers are now focusing more on eco-friendly and green materials. A biocomposite offers a good balance of strength and stiffness ratio, bending and membrane mechanical properties, balanced thermal distortion stability, reduced weight and cost, improved fatigue resistance, reduced notch sensitivity, and, comparatively, better performance than synthetic composites. Yet, due to the complex anisotropy of the composite material, the inspection and detection of inner defects become a challenge. Long-pulse thermography is one of the non-destructive evaluations (NDEs) used to detect defects in composite materials. However, very limited research has been carried out on the usage of a low-resolution infrared camera to perform defect or damage inspection on flax composite laminates. In this paper, an experimental setup of a long pulse thermography system using low-resolution infrared camera was performed on flax bio-composite to identify impact and lightning damage. The result highlights that with control parameters, a low-resolution infrared camera has the capability to capture the lightning and impact defects of flax biocomposites using the long-pulse thermography system. An image processing method is then applied to the defect to improve the quality of defect detection and reduce background noise.

Increasing high-temperature fatigue resistance of polysynthetic twinned TiAl single crystal by plastic strain delocalization

Polysynthetic twinned (PST) TiAl single crystal possesses great potentials for high-temperature applications due to its excellent combination of strength, ductility and creep resistance. However, a critical property for high-temperature application of such material involving high-temperature fatigue properties remains unknown. Here, the high-temperature high-cycle fatigue performance of PST TiAl single crystal has been studied. The result shows that PST TiAl single crystal can withstand more than 107 cyclic loadings at 975 °C under a stress amplitude of 270 MPa, which is significantly higher than traditional TiAl alloys. Experimental observations and atomistic simulations indicate that the improvement of fatigue resistance is attributed to the plastic strain delocalization in uniform lamellar structure, and the plastic deformation is well-distributed and sufficient in each lamella. Even in the α2 lamella with difficult slippage, a large number of stacking fault structures can be observed. The 〈c + a〉 dislocations in α2 tend to dissociate into a Frank partial with b = 1/6 <22¯03¯>, forming a ribbon of I1 fault which ensures the continuity of deformation.

Delamination and Manufacturing Defects in Natural Fiber-Reinforced Hybrid Composite: A Review.

In recent years, most boat fabrication companies use 100% synthetic fiber-reinforced composite materials, due to their high performance of mechanical properties. In the new trend of research on the fabrication of boat structure using natural fiber hybrid with kevlar/fiberglass-reinforced composite, the result of tensile, bending, and impact strength showed that glass fiber-reinforced polyester composite gave high strength with increasing glass fiber contents. At some point, realizing the cost of synthetic fiber is getting higher, researchers today have started to use natural fibers that are seen as a more cost-effective option. Natural fibers, however, have some disadvantages, such as high moisture absorption, due to repelling nature; low wettability; low thermal stability; and quality variation, which lead to the degradation of composite properties. In recent times, hybridization is recommended by most researchers as a solution to natural fiber’s weaknesses and to reduce the use of synthetic fibers that are not environmentally friendly. In addition, hybrid composite has its own special advantages, i.e., balanced strength and stiffness, reduced weight and cost, improved fatigue resistance and fracture toughness, and improved impact resistance. The synthetic–nature fiber hybrid composites are used in a variety of applications as a modern material that has attracted most manufacturing industries’ attention to shift to using the hybrid composite. Some of the previous studies stated that delamination and manufacturing had influenced the performance of the hybrid composites. In order to expand the use of natural fiber as a successful reinforcement in hybrid composite, the factor that affects the manufacturing defects needs to be investigated. In this review paper, a compilation of the reviews on the delamination and a few common manufacturing defect types illustrating the overview of the impact on the mechanical properties encountered by most of the composite manufacturing industries are presented.

Cyclic Deformation Induced Residual Stress Evolution and 3D Short Fatigue Crack Growth Investigated by Advanced Synchrotron Tomography Techniques.

Diffraction and phase contrast tomography techniques were successfully applied to an austenitic–ferritic duplex stainless steel representing exemplarily a metallic material containing two phases with different crystal structures. The reconstructed volumes of both phases were discretized by finite elements. A crystal plasticity finite-element analysis was executed in order to simulate the development of the experimentally determined first and second order residual stresses, which built up due to the manufacturing process of the material. Cyclic deformation simulations showed the single-grain-resolved evolution of initial residual stresses in both phases and were found to be in good agreement with the experimental results. Solely in ferritic grains, residual stresses built up due to cyclic deformation, which promoted crack nucleation in this phase. Furthermore, phase contrast tomography was applied in order to analyze the mechanisms of fatigue crack nucleation and short fatigue crack propagation three-dimensionally and nondestructively. The results clearly showed the significance of microstructural barriers for short fatigue crack growth at the surface, as well as into the material. The investigation presented aims for a better understanding of the three-dimensional mechanisms governing short fatigue crack propagation and, in particular, the effect of residual stresses on these mechanisms. The final goal was to generate tailored microstructures for improved fatigue resistance and enhanced fatigue life.

Effect on overall fatigue performance of varying thickness of an intermetallic sublayer within a soft multilayer coating

A series of 2IML multilayer coatings (composed of two hard intermetallic (IML) layers and two soft sublayers) with the different thickness of the first IML sublayer have been built to develop our mechanistic understanding of what controls its fatigue performance. Experimental investigations of these multilayer coatings reveal that decreasing the IML-Top layer’s thickness provides improved fatigue resistance. This improvement could be linked to: (1) the increased difficulty of surface crack initiation due to the limitation of the strain ranges experienced at the top surface and (2) the shorter crack propagation period in a thinner IML-Top layer.

Nanocomposite NiTi shape memory alloy with high strength and fatigue resistance.

Many established, but also potential future applications of NiTi-based shape memory alloys (SMA) in biomedical devices and solid-state refrigeration require long fatigue life with 107-109 duty cycles1,2. However, improving the fatigue resistance of NiTi often compromises other mechanical and functional properties3,4. Existing efforts to improve the fatigue resistance of SMA include composition control for coherent phase boundaries5-7 and microstructure control such as precipitation8,9 and grain-size reduction3,4. Here, we extend the strategy to the nanoscale and improve fatigue resistance of NiTi via a hybrid heterogenous nanostructure. We produced a superelastic NiTi nanocomposite with crystalline and amorphous phases via severe plastic deformation and low-temperature annealing. The as-produced nanocomposite possesses a recoverable strain of 4.3% and a yield strength of 2.3 GPa. In cyclic compression experiments, the nanostructured NiTi micropillars endure over 108 reversible-phase-transition cycles under a stress of 1.8 GPa. We attribute the enhanced properties to the mutual strengthening of nanosized amorphous and crystalline phases where the amorphous phase suppresses dislocation slip in the crystalline phase while the crystalline phase hinders shear band propagation in the amorphous phase. The synergy of the properties of crystalline and amorphous phases at the nanoscale could be an effective method to improve fatigue resistance and strength of SMA.

Mss51 deletion increases endurance and ameliorates histopathology in the mdx mouse model of Duchenne muscular dystrophy.

Mitochondrial derangement is an important contributor to the pathophysiology of muscular dystrophies and may be among the earliest cellular deficits. We have previously shown that disruption of Mss51, a mammalian skeletal muscle protein that localizes to the mitochondria, results in enhanced muscle oxygen consumption rate, increased endurance capacity, and improved limb muscle strength in mice with wildtype background. Here, we investigate whether Mss51 deletion in the mdx murine model of Duchenne muscular dystrophy (mdx-Mss51 KO) counteracts the muscle pathology and mitochondrial irregularities observed in mdx mice. We found that mdx-Mss51 KO mice had increased myofiber oxygen consumption rates and an amelioration of muscle histopathology compared to mdx counterparts. This corresponded with greater treadmill endurance and less percent fatigue in muscle physiology, but no improvement in forelimb grip strength or limb muscle force production. These findings suggest that although Mss51 deletion ameliorates the skeletal muscle mitochondrial respiration defects in mdx and improves fatigue resistance in vivo, the lack of improvement in force production suggests that this target alone may be insufficient for a therapeutic effect.

Chemical and rheological characteristics of rejuvenated bitumen with typical rejuvenators

In recent years, reclaimed asphalt pavement (RAP) is widely used in pavement construction because of its merits on both economic and environmental aspects. The use of RAP contributes to significant reduction on resource consumption, construction emission and the overall construction costs. To better utilize RAP, different rejuvenators are applied to soften the aged bitumen and enhance the blending efficiency between new and aged bitumen. Although the engineering performance of RAP mixtures has been well studied, the interaction among new bitumen, aged bitumen and rejuvenators still remains unclear. This study is conducted for rejuvenating mechanism investigation by chemical and rheological analyses. To achieve this goal, three typical rejuvenators (soft bitumen, warm mix surfactant, and bio-rejuvenator) were mixed with aged bitumen. Various tests including Dynamic Shear Rheometers (DSR), Fourier Transform Infrared (FTIR) spectroscopy and Gel Permeation Chromatography (GPC) were performed. It is found that all three rejuvenators exhibited certain effect on restoring rheological performance of aged bitumen. The softening effect of DAT and bio-rejuvenator were strongest when aged bitumen percentages were 30% and 80% respectively. The incorporation of appropriate percentage of aged bitumen improved the fatigue lives of rejuvenated bitumen. Soft bitumen exhibited the optimal performance on improving fatigue resistance of rejuvenated bitumen. Additionally, the alterations of functional group indices and molecular distribution can be considered as explanations for the regenerating effect of rejuvenators. Moreover, the sulfoxide index of FTIR and three GPC parameters can be used as reliable indicators to predict the rheological properties of rejuvenated bitumen.

Study on the Influence of Compression Ratio on the Rail Contact Fatigue Resistance Property and Its Mechanism.

Contact fatigue resistance properties of four commercial steel rails were systematically studied and compared. The contact fatigue limit cycles, fracture toughness, and fatigue crack growth rate of the corresponding rails with different compression ratios were tested and analyzed, which showed a close relationship between them. Moreover, microstructures of the rails were carefully observed by using the TEM to elucidate the scientific mechanisms. Observations and obtained results indicated that pearlite lamellar spacing further decreased with the rise of compression ratio, which greatly and rightly contributed to the improved fatigue resistance property.

Investigating the fatigue performance of soft multilayer coatings with varying locations of an intermetallic interlayer

A multilayer coating system containing two hard intermetallic layers (IMLs) within a soft metallic system provides improved fatigue performance. To further optimise this system, various coatings with different locations of the intermediate intermetallic (IML-Top) interlayer were manufactured and experimentally investigated. Their characteristics were assessed and fatigue performances were compared, revealing the improvement of fatigue resistance by locating the IML-Top layer close to the top overlay coating surface. The mechanisms, based on post-test observations of crack morphology, are identified as (1) improved retardation of crack initiation and (2) improved crack growth resistance provided by the shielding effect of the IML-Top layer.

Polymer‐silica additive as a modifier of tribological properties of ecological grease, improvement of fatigue resistance

AbstractThe influence of polymer additive (polytetrafluoroethylene) in grease based on paraffin oil on the resistance to fatigue wear (pitting) was investigated of rolling contact. The research results revealed that grease containing a polymer caused an increase in resistance to fatigue. It was examined whether the additive affects the properties of the grease, including rheological (investigated with the use of rheometer operated in the cone/plate configuration) and thermal (determined using the Differential Scanning Calorimetry) to check their relationship with a resistance to fatigue. A scanning electron microscope equipped with an energy dispersive spectrometer was used to determine if a polymer was present on wear trace. Then the sources of chemical elements were analysed with the use of X‐ray photoelectron spectroscopy to explain the improvement of resistance to fatigue. The relation between rheological properties and resistance to fatigue was shown, and the presence of polymer in friction contact was observed.

Investigation on rheological properties of bitumen based on rheological parameters of maltenes

ABSTRACT Previous research studies have indicated that each bituminous component plays a different role in rheological properties of bitumen. However, a few literature studies focus on rheological parameters of bitumen at component level. This paper aims to investigate the intuitive influence of rheological parameters of maltenes on rheological properties of bitumen. Saturates, aromatics, resins and asphaltenes (SARA) were firstly separated from two base bitumens and Styrene–butadiene–styrene (SBS)-modified bitumen. Dynamic shear rheometer (DSR) was applied to characterise the rheological properties of three bitumens and their maltenes. Temperature and frequency sweep tests were conducted to obtain six rheological parameters, including complex modulus, phase angle, complex modulus index, rutting factor, fatigue factor and rheology cracking index. The results indicate that the elasticity of base bitumen in low-temperature stage is mainly provided by resins and aromatics compared with the sole contribution of aromatics in SBS bitumen. The promotion effect for enhancing anti-rutting ability of resins in base bitumen is superior to that of SBS bitumen. Saturates, with a rutting factor of less than 1 kPa, lead to a passive effect on deformation resistance at higher temperatures of bitumen. Maltenes show a different contribution rate of improvement of fatigue resistance in a descending order of saturates, resins and aromatics. Aromatics with superior cracking resistance contribute to the enhancement of ductility for bitumen in contrast to resins with a larger rheology cracking index. The intuitive analysis on maltenes will facilitate further investigation of the interaction mechanism for bitumen modification and rejuvenation so as to enhance rheological properties of bitumen.

A lifetime assessment and prediction method for large area solder joints

Mechanical bending fatigue experiments were conducted on large area Pb-rich and SnSb-based model solder joints consisting of Cu-strip/solder/DCB substrates. Experimental lifetime curves in the range between 105 and 108 loading cycles at room and elevated temperature showed an improved fatigue resistance for SnSb alloys. Crack length as a function of loading cycles (da/dN) was determined for selected samples to study the cyclic degradation behaviour of the solder layer. Crack initiation and propagation in the joints was modelled on the basis of a damage accumulation rule considering the strain rate and temperature dependency of the solder alloy. Application of the FEM model to large area solder joints allowed calculation of the incremental advancement of the crack front, determination of the crack growth rate (da/dN) and prediction of lifetime under a given loading condition.

Photochromic microcapsules anchored on cotton fabric by layer-by-layer self-assembly method with erasable property

Photochromic materials have great potential applications in many fields due to their reversible color change under light irradiation. Herein, a novel photochromic cotton fabric with high fatigue resistance was creatively fabricated via a facile electrostatic layer-by-layer self-assembly technology of photochromic microcapsules and sodium alginate. Chitosan was used to encapsulate photochromic dyes to form microcapsules to improve fatigue resistance, meanwhile, as the wall material of microcapsules in weak acid environment can provide the positive charge needed for electrostatic layer-by-layer self-assembly process. After the anionic modification of cotton fabric to achieve negative charge, electrostatic layer-by-layer self-assembly was taken place between -NH3+ on the wall material of microcapsules and -COO− in sodium alginate under the condition of pH = 5. For clear characterization of the regular charge changes of fabric surface during the assembly process, the methylene blue (a kind of cationic dye) dyeing of cotton fabrics was carried out, the K/S and Lab value of the dyed fabric showed a regular “odd-even” oscillation. The assembled five-layer microcapsules fabric can change from colorless to purple rapidly within 12 s under UV light, and reversibly return to the original state under the irradiation of green light quickly in 90 s. It can maintain excellent reusability photochromic performance (94.65%) after more than 20 reversible color-changing cycles, implying the good reusability in erasable optical data storage. Furthermore, since the photochromic dyes can absorb UV light, the as-prepared photochromic cotton fabric has excellent UV protection properties.

Enhancement of fatigue resistance by overload-induced deformation twinning in a CoCrFeMnNi high-entropy alloy

We examined fatigue-crack-growth behaviors of CoCrFeMnNi high-entropy alloys (HEAs) under as-fatigued and tensile-overloaded conditions using neutron-diffraction measurements coupled with diffraction peak-profile analyses. We applied both high-resolution transmission electron microscopy (HRTEM) and neutron-diffraction strain mapping for the complementary microstructure examinations. Immediately after a single tensile overload, the crack-growth-retardation period was obtained by enhancing the fatigue resistance, as compared to the as-fatigued condition. The combined mechanisms of the overload-induced larger plastic deformation, the enlarged compressive residual stresses and plastic-zone size, the crack-tip blunting ahead of the crack tip, and deformation twinning governed the pronounced macroscopic crack-growth-retardation behavior following the tensile overload. A remarkable fracture surface of highly-periodic serrated features along the crack-propagation direction was found in the crack-growth region immediately after the tensile overload. Moreover, a transition of plastic deformation from planar dislocation slip-dominated to twinning-dominated microstructures in the extended plastic zone was clearly observed at room temperature in the overloaded condition, in accordance with the simulated results by a finite element method (FEM). The above tensile overload-induced simultaneously combined effects in the coarse-grained CoCrFeMnNi shed light on the improvement of fatigue resistance for HEAs applications.

Improvement of Fatigue Resistance of Epoxy Composite with Heterogeneous Solid-State Self-Healing System

The purpose of this research study was to investigate the improvement in fatigue life parameters and static strength residues of heterogeneous solid-state of the self-healing resin after exposure to fatigue cycles. The healing system is based on the thermoplastic-thermosetting semi-interpenetrating network. This system employs a thermosetting resin, into which a linear thermoplastic of poly(vinyl chloride) (PVC), poly(vinyl alcohol) (PVA), polyethylene (PE) or polypropylene (PP) as is dissolved. Upon heating a fractured resin system at a specific temperature, the heterogeneous resin blend undergoes a volumetric thermal expansion of healing agent within the matrix resin for crack recovery. Under the Compact tension (CT) test and within the third healing cycle, the modified resin with PVC has the average percentage recovery of 75-48% compared with PP, PE, or PVA at around 67-31%, respectively. The modified epoxy fatigue life with PVC and PP was shown to be increased by a factor of about 1.5 and 1.1 times after healing periods. The healable (modified) resin also showed an improvement in residual strength than the control resin after exposure to fatigue cycles. The fatigue-healing process was proven through the surface and cross-section resin morphology analysis using a microscopy optic and scanning electron microscope (SEM). On the whole, the heterogeneous solid-state selfhealing system has proven to be effective in obstructing fatigue crack propagation, effectively improved the self-healing polymeric material to achieve higher life extension.

Determination of weldability study on mechanical properties of dissimilar Al-alloys using Friction stir welding process

Abstract Friction stir welding is a solid-state joining process, which is used for joining the two materials in numerous critical application and much other commercial importance. The Aluminum alloys AA2024 and AA7075, which are heat-treatable alloys, it is widely used in aerospace, automotive and transportation industries. The aluminum alloys exhibit greater strength, good impact, superior hardness, excellent corrosion resistance, improve fatigue resistance and lesser density. The current investigation aims at joining of the dissimilar material of AA2024 and AA7075 Al-alloys by the effect of different welding parameters. The tool rotational speed was varied between 1000 rpm and 1400 rpm, welding speed between 20 mm/min and 40 mm/min and axial force of 4KN is kept at constant. The microstructure examination was performed using Scanning electron microscopy (SEM) and the mechanical properties were evaluated through the tensile test. The microstructure examination result displays the appearance of coarsening grains, when there the rotational speed is increased as a reason of more heat input and occurrence of dynamic recrystallization in the deformed zone. Furthermore, the tensile strength is increasing with a decrease in welding speed of Friction stir process (20 m/min & 1000 rpm). The corrosion properties (salt spray) test illustrates that no type of corrosion occurs in all the friction stir samples for the exposure period of 48 h.

Comparative study of conventional and deep cryogenic treatment of AISI M3:2 (EN 1.3395) high-speed steel

This study focuses on the changes in mechanical and tribological properties of selected AISI M3:2 high-speed steel when exposed to deep cryogenic treatment (DCT). At the same time, it provides a comparative study of DCT effectiveness on two different steel grades (AISI M3:2 and AISI M2). The impact of DCT is determined by comparing mechanical and tribological properties of selected steels when exposed to conventional vacuum heat treatment and heat treatment comprising DCT. The properties investigated include hardness, fracture toughness, fatigue resistance under cycling bending as well as abrasive wear resistance. This study is also one of the first to disclose the influence of DCT on the properties of M3:2 steel. The results of this investigation show that DCT positively influences both steels, exhibiting higher fracture toughness, improved fatigue resistance and conditionally better wear resistance, while inducing minimal changes in hardness. This study also provides an input on the influence Co dynamics in DCT treated steels, at which the Co grade steel shows improvement of its properties with DCT.