Under cyclic fatigue load, multiple cracks would significantly deteriorate the service life of the components with respect to the case of a single crack owing to the crack interaction. The present study aims to explore the effect of crack interaction on the fatigue growth behaviour of samples with different crack offset. In this study, fatigue crack growth tests were performed for samples containing a single crack and non-collinear cracks of different crack offset in an aluminum-lithium alloy. It was shown that the two facing non-collinear cracks changed their growth direction when the cracks were overlapped, resulting in load mode transfers from mode I to I + II mixed mode. Then, the interaction behaviour was studied by establishing the finite element models to calculate the stress intensity factor K of samples with different crack offset. The results indicated that the K decreased, largely owing to the shielding effect as the two cracks overlapped, leading to retardation of crack growth in the position of overlap, especially for the specimens with a small crack offset. It was also shown that the interaction effect could change from positive to negative during the process of the multiple cracks' growth, thus leading to the acceleration or deceleration of crack growth rates, suggesting that the influence of interaction on cracks' growth behaviour could vary with the different stages of crack growth.
Aiming to investigate the propagation behaviour of distortion-induced fatigue cracks in steel bridge web gaps, multi-scale numerical analysis models were built based on fracture mechanics theory and extended finite element method (XFEM), combining with the full-scale fatigue tests data. Propagation behaviours of representative fatigue cracks in vertical stiffener web gaps and horizontal gusset plate web gaps were analysed. Finite element models of welds connecting web, vertical stiffener and horizontal gusset plate were built, and the welding residual stresses of such details were analysed. Significant transverse welding residual tensile stresses exist at stiffener web weld toes for web gap details. Residual stress measurements were conducted, and the crack shape and the propagation direction path were basically the same with that in the numerical simulation, indicating that the numerical simulation results were relatively reliable. Furthermore, the welding residual stress fields were considered in the crack propagation analysis models. Representative fatigue cracks at web gaps are Mode I leading mixed-mode cracks of Modes I, II and III. Crack propagation considering welding residual stress has faster propagation rate and is more consistent with fatigue test results. The welding residual stress cannot be ignored for analysis and assessment of distortion-induced fatigue cracks in steel bridges.
Recently, there has been a growing interest in advancing plant-based or cultured meat substitutes as environmentally and ethically superior alternatives to traditional animal-derived meat. In pursuit of simulating the authentic meat structure, a composite fiber composed primarily of soy protein isolates (SPIs) was fashioned, employing a fiber-based plant-based analog meat construct. To refine the spinning process and enhance fiber quality, we employed ultrasound treatment, a physical modification technique, to scrutinize its influence on SPI protein structure. This inquiry extended to the examination of the interplay between sodium alginate (SA) and SPI, as well as the impact of salt ions on the SA and ultrasound soy protein isolates (USPI) interaction. A comprehensive exploration encompassing ultrasound treatments and salt concentrations within the composite solution, along with their repercussions on composite fiber characterization, with a rise in negative zeta potential value, states the ultrasound treatment fosters protein aggregation. Moreover, the introduction of salt augments protein aggregation as salt content escalates, ultimately resulting in a reduced structural viscosity index and improved spinnability. The presence of Ca2+ ions during the coagulation process leads to interactions with SA. The involvement of ultrasound prompts the exposure of hydrophilic amino acid segments in the protein to water, leading to the development of a more porous structure. Solely under the influence of ultrasound, the fiber exhibits 5% higher water-holding capacity and superior mechanical properties while maintaining comparable thermal stability.
Abstract Local postweld heat treatment (PWHT) is usually employed in field fabrication of large-sized ASME SA-335 Grade P92 steel pipes. Internal air flow in pipes that arise from field fabrication can result in considerable convection losses on the inside surface of the pipe when the pipe is not strictly sealed off. Welding and local PWHT experiments of a large diameter P92 steel pipe were conducted both with and without internal air flow, and temperature field of both sides of the pipe was measured. The conjugate heat transfer between the pipe and the internal air is simulated using computational fluid dynamics (CFD) method. The effect of internal air flow on temperature field was further investigated. Results indicate that temperature gradient along through-thickness direction and axial direction during local PWHT is significantly increased due to internal air flow. The increasing rate of temperature difference between inner and outer surface at weld centerline to internal air velocity is about 14.5 °C/(m s−1). The maximum temperature is no longer located at the weld centerline, which will lead to a risk of overheating. The temperature drop is severer in the air inlet side than air outlet side at same distance from weld centerline. For local PWHT to be successful, the internal air flow should be strictly limited during local PWHT; otherwise, the width of heated band (HB) should be extended.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)