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Scrap tire rubber and nylon fiber are waste materials that could potentially be recycled and used to improve the mechanical properties of asphalt pavement. The objective of this research was to investigate the properties of scrap tire rubber and nylon fiber (R-F) modified warm mix asphalt mixture (WMA). The high-temperature performance was estimated by the Hamburg wheel-tracking testing (HWTT) device. The low-temperature cracking performance was evaluated by the disk-shaped compact tension (DCT) test and the indirect tensile strength (IDT) test. The stress and strain relationship was assessed by the dynamic modulus test at various temperatures and frequencies. The extracted asphalt binder was evaluated by the dynamic shear rheometer (DSR). Pavement distresses were predicted by pavement mechanistic-empirical (M-E) analysis. The test results showed that: (1) The R-F modified WMA had better high-temperature rutting performance. The dynamic modulus of conventional hot mix asphalt mixture (HMA) was 21.8%~103% lower than R-F modified WMA at high temperatures. The wheel passes and stripping point of R-F modified WMA were 2.17 and 5.8 times higher than those of conventional HMA, respectively. Moreover, the R-F modified warm mix asphalt had a higher rutting index than the original asphalt. (2) R-F modified WMA had better cracking resistance at a low temperature. The failure energy of the R-F modified WMA was 24.3% higher than the conventional HMA, and the fracture energy of the R-F modified WMA was 7.7% higher than the conventional HMA. (3) The pavement distress prediction results showed the same trend compared with the laboratory testing performance in that the R-F modified WMA helped to improve the IRI, AC cracking, and rutting performance compared with the conventional HMA. In summary, R-F modified WMA can be applied in pavement construction.

Cold in-place recycling (CIR) asphalt mixtures are an attractive eco-friendly method for rehabilitating asphalt pavement. However, the on-site CIR asphalt mixture generally has a high air void because of the moisture content during construction, and the moisture susceptibility is vital for estimating the road service life. Therefore, the main purpose of this research is to characterize the effect of moisture on the high-temperature and low-temperature performance of a CIR asphalt mixture to predict CIR pavement distress based on a mechanistic–empirical (M-E) pavement design. Moisture conditioning was simulated by the moisture-induced stress tester (MIST). The moisture susceptibility performance of the CIR asphalt mixture (pre-mist and post-mist) was estimated by a dynamic modulus test and a disk-shaped compact tension (DCT) test. In addition, the standard solvent extraction test was used to obtain the reclaimed asphalt pavement (RAP) and CIR asphalt. Asphalt binder performance, including higher temperature and medium temperature performance, was evaluated by dynamic shear rheometer (DSR) equipment and low-temperature properties were estimated by the asphalt binder cracking device (ABCD). Then the predicted pavement distresses were estimated based on the pavement M-E design method. The experimental results revealed that (1) DCT and dynamic modulus tests are sensitive to moisture conditioning. The dynamic modulus decreased by 13% to 43% at various temperatures and frequencies, and the low-temperature cracking energy decreased by 20%. (2) RAP asphalt incorporated with asphalt emulsion decreased the high-temperature rutting resistance but improved the low-temperature anti-cracking and the fatigue life. The M-E design results showed that the RAP incorporated with asphalt emulsion reduced the international roughness index (IRI) and AC bottom-up fatigue predictions, while increasing the total rutting and AC rutting predictions. The moisture damage in the CIR pavement layer also did not significantly affect the predicted distress with low traffic volume. In summary, the implementation of CIR technology in the project improved low-temperature cracking and fatigue performance in the asphalt pavement. Meanwhile, the moisture damage of the CIR asphalt mixture accelerated high-temperature rutting and low-temperature cracking, but it may be acceptable when used for low-volume roads.

The present work investigates low-temperature cracking performance of fiber-reinforced asphalt concrete (FRAC) materials. Different asphalt mixtures containing various amounts of fiber were explored. Disk-shaped compact tension (DC(T)), indirect tensile (ID(T)), and acoustic emission (AE) tests were conducted to evaluate cracking performance of FRAC materials. In addition, the AE test was utilized to investigate low-temperature fracture in fiber-modified asphalt binders. Results demonstrated that incorporating fibers improved low-temperature cracking behavior of asphalt mixtures by increasing the fracture energy by 4.3% and tensile strength by 5.1% per ounce of fiber added to the material. Moreover, it was observed that presence of fibers enhanced fracture softening behavior of FRAC mixtures. Asphalt binder results showed that fiber-modified binders consistently exhibited lower embrittlement temperatures indicating higher resistance against thermal cracking. The AE hit counts in both FRAC mixtures and asphalt binders significantly decreased at the average rate of 8.3 and 9.6% per ounce of fiber added to mixtures and asphalt binders, respectively. Finally, a cracking performance prediction model was developed for FRAC materials using the machine learning elastic-net regression approach.

This research utilizes both single crystal and polycrystalline models to probe the fatigue crack propagation mechanism in pure silver via molecular dynamics (MD) simulations. A comprehensive validation approach at both micro and macro scales, incorporating transmission electron microscopy (TEM), electron backscatter diffraction (EBSD), and compact tension (CT) specimen fatigue testing, is developed to verify the reliability of simulation models and results. Simulation findings indicate that the initial crack orientation significantly influences crack propagation. As the crack advances within the crystal, two primary crack propagation mechanisms are discerned: (1) nano-voids appear at the crack tip, and the crack propagates by continuously aggregating with the nano-voids ahead; (2) the formation of Stair-rod dislocations and V-shape stacking faults due to dislocation reactions and slip band movements impedes crack propagation, accompanied by the dislocation reaction of Shockley partial dislocations ( 1 6   ) generating Hirth dislocations ( 1 6   ). The dislocation reaction is verified through the dislocation analysis of the crack tip area of the CT specimen after fatigue experiment by using TEM. In addition, the results of this study show that the angle between the direction of crack propagation and the grain boundary affects the fatigue crack propagation, e.g. when the angle is less than 60°, the crack rapidly propagates along the grain boundary. The orientation distribution function (ODF) results of EBSD can verify that the polycrystalline model containing 30 grains is a reliable model for the MD simulation of behavior of the crack tip of CT specimen. Lastly, the Paris law constants for pure silver are determined as m  = 3.72 and lg C  = − 10.77, providing a reference for the fatigue analysis and life prediction of silver components or silver soldering pots in engineering applications.

For allowable defect analyses, the fracture toughness of materials needs to be accurately predicted. In this regard, a lower fluctuation of fracture toughness can lead to reduction in safety and economic risks. Crack tip opening displacement (CTOD), which is the representative parameter for fracture toughness, can be measured by various methods, such as the δ5, the J-conversion method, the single clip gauge method, and the double clip gauge method. When calculating CTOD from test results, the principle of similar triangles, which adopts the plastic hinge model, is influenced by the rotation factor, rp. Therefore, in order to reduce the fluctuation of CTOD, the exact value of rp must be defined. This study investigates various methods to predict fracture toughness in metallic materials, and assess the pros and cons of each method. Moreover, the equation of rp is modified by using a double clip gauge in compact tension (CT) to reduce the fluctuation of CTOD. The rp value is derived from 0.55 to 0.68, using the double clip gauge method. Finite element analysis is used to derive the rp values, which range from 0.50 to 0.66, in order to verify the validity of the derived rp values. This ensures the validity of the rp value derived from the experiment. In addition, the fluctuation of CTOD, based on the modified equation of rp, is lower than that using the single clip gauge method, according to BS 7448.

Additive manufacturing offers greater flexibility in the design and fabrication of structural components with complex shapes. However, the use of additively manufactured parts for load-bearing structural applications, specifically involving cyclic loading, requires a thorough investigation of material fatigue properties. These properties can be affected by many factors, including residual stresses and crack tip shielding mechanisms, which can be very different from those of conventionally manufactured materials. This research focuses on super duplex stainless steels (SDSSs) fabricated with wire arc additive manufacturing (WAAM) and investigates their fatigue crack growth rates and the net effect of crack tip shielding mechanisms. Using the compliance-based method, we measured crack tip opening loads in compact tension (CT) specimens with cracks propagating longitudinally and transversely to the WAAM deposition direction. It was found that fatigue crack growth rates were very similar in both directions when correlated by the effective stress intensity factor range. However, the differences in crack tip opening loads explain a quite significant influence of the deposition direction on the fatigue life.

Multi-material additive manufacturing (MMAM) enables the fabrication of structures with synergistic properties. However, the interfacial adhesion between dissimilar polymers remains a critical weakness that compromises structural integrity. To address this, the effect of layer thickness (LT) on the bending and interlayer adhesion performance of polyethylene terephthalate glycol (PETG), polylactic acid (PLA), and PLA/PETG multi-material (MM) specimens produced by Fused Filament Fabrication (FFF) was investigated in this study. The bending characteristics of specimens were determined using three-point bending (3P-B) tests. Compact tension (CT) and short beam shear (SBS) tests were conducted to determine interlayer adhesion performance. Test specimens were fabricated using LTs of 0.1 mm, 0.2 mm, and 0.3 mm via a dual-nozzle printer. CT tests revealed that the adhesion strength of PETG with increased LT decreased by around 50%. However, for the PLA and MM specimens, this decrease is limited to approximately 29%. SBS tests showed that there is an obvious correlation between the shear strength and LT. For the 0.1 mm LT, PETG and PLA specimens exhibited the highest and lowest shear strength, respectively. The MM specimens performed moderately in terms of shear strength. In the case of 3P-B tests, in contrast to the results of the SBS tests, the PLA exhibited the highest performance, followed by the MM, while the PETG had the lowest. For the 0.1 mm LT, the MM specimens exhibited the highest AE and SAE values, as well as the second highest short beam and bending strengths. It can therefore be deduced that, in scenarios where stress concentrations are subject to change, MM is a safer option than PLA and PETG for the 0.1 mm LT.

The presented text deals with research into the influence of the printing layers’ orientation on crack propagation in an AlSi10Mg material specimen, produced by additive technology, using the Direct Metal Laser Sintering (DMLS) method. It is a method based on sintering and melting layers of powder material using a laser beam. The material specimen is presented as a Compact Tension test specimen and is printed in four different defined orientations (topology) of the printing layers—0°, 45°, 90°, and twice 90°. The normalized specimen is loaded cyclically, where the crack length is measured and recorded, and at the same time, the crack growth rate is determined. The evaluation of the experiment shows an apparent influence of the topology, which is essential especially for possible use in the design and technical preparation of the production of real machine parts in industrial practice. Simultaneously with the measurement results, other influencing factors are listed, especially product postprocessing and the measurement method used. The hypothesis of crack propagation using Computer Aided Engineering/Finite Element Method (CAE/FEM) simulation is also stated here based on the achieved results.

A comprehensive numerical investigation of Fatigue Crack Growth (FCG) under negative stress ratios (R < 0) was conducted using the Finite Element Method (FEM) and the ANSYS Benchmark 19.2 SMART crack growth module on modified Compact Tension (CT) specimens. This study addresses the critical challenge posed by the compressive portion of cyclic loading, which traditional Linear Elastic Fracture Mechanics (LEFM) models often fail to capture accurately due to the complex interaction of crack closure and reversed plastic zones. The analysis focused on the evolution of the von Mises stress and maximum principal stress distributions at the crack tip across a range of stress ratios, including R = 0.1, −0.1, −0.2, −0.3, −0.4, −0.5, and −1.0. The results demonstrate a significant inverse correlation between fatigue life cycles and the magnitude of the negative stress ratio, consistent with the detrimental effect of increasing tensile stress. Crucially, the numerical simulation successfully captured the non-monotonic behavior of the crack tip stress field, revealing that the compressive load phase substantially alters the effective stress intensity factor range and the crack growth path, which was governed by the Maximum Tangential Stress (MTS) criterion. This research provides a validated computational methodology for accurately predicting FCG life in engineering components subjected to demanding, fully reversed, or compressive–dominant cyclic loading environments.

The increasing adoption of fuel-cell vehicles, driven by their environmentally friendly zero-emission features, is a crucial step towards reducing environmental damage. However, current research primarily focuses on stress-related aspects of pressurized tanks, leaving a critical knowledge gap regarding potential fractures within the tank’s body, which can accelerate pressure tank failure. This study aims to address this concern by analyzing alternative fiber materials beyond carbon fiber in a finite element analysis model, with the primary objective of enhancing the durability of pressurized tanks for hydrogen-fueled vehicles against fracture loading. The investigation revolves around the fracture behavior of type-III high-pressure composite tanks, pivotal components for the secure operation of hydrogen-powered fuel cell vehicles. Various configurations of Al6061 and Al7178 liners coupled with six distinct fiber materials and six different winding orientations [(± 15/90) n ] T , (± 30/90)n, [(± 45/90) n ] T , [(± 55/90) n ] T , [(± 60/90) n ] T , and [(± 75/90) n ] T have been meticulously assessed to provide an in-depth analysis of fracture energy behavior in composite tanks. The stress intensity factor ( G I ) was computed using a compact tension model developed in Abaqus, for all composite variations under consistent conditions, providing a robust foundation for understanding the fracture behavior. Additionally, MATLAB was utilized to calculate the effective elastic modulus for the selected composite materials. Subsequently, the strain energy release rate was derived from the relationship between the G I and the effective elastic modulus of composite tanks. The derived G I revealed notable improvements in fracture resistance for specific composite shells and liner materials, particularly at higher winding orientations. The results emphasized the superior performance of boron-epoxy composite shells for type-III pressure vessels, exhibiting the lowest G I values and exceptional crack resistance. Notably, Al7178 combined with boron-epoxy outperformed Al6061 composites at higher winding orientations, while glass–epoxy shells exhibited greater susceptibility to crack propagation, especially in specific ply orientations.