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To illuminate brittle and ductile fracturing of magma, we investigated bubble expansion and fracturing in two contrasting fluids: a Maxwell‐type viscoelastic fluid and a Bingham‐type yield‐strength fluid. Measurements of the complex shear modulus, G′ + iG″ (i is the imaginary unit), under small‐strain oscillation showed that both fluids are elastic (G′ > G″) with similar rigidity. Viscous behavior (G′ < G″) appeared at lower frequency in the Maxwell fluid but at larger strain in the Bingham fluid. When we injected air into the Maxwell fluid, bubbles expanded viscously at low flux, fractured in a brittle manner at high flux, and behaved transitionally at intermediate flux. In contrast, we observed no fracturing in the Bingham fluid. This demonstrates that the G′ > G″ condition is insufficient to infer that brittle fracturing can occur. Brittle fracturing of the Maxwell fluid occurred not at a critical strain rate but under decreasing strain rate and increasing stress. Plain Language Summary The flow‐to‐fracture transition of magma is an essential process controlling eruption explosivity. This transition has been explained based on the linear Maxwell viscoelastic model: magma can flow slowly but breaks in a brittle manner under rapid deformation. The Bingham model represents another type of fluid‐solid transition: a material flows under a sufficiently large force but behaves elastically below this force. The present study investigates bubble growth and fracture by air injection in Maxwell‐type and Bingham‐type fluids, both having similar elasticity. We demonstrate that brittle fracture occurs in the Maxwell fluid at high air flux but never in the Bingham fluid. Detailed observations of the deformation until brittle fracture reveals a stress increase and strain rate decrease. The fracture onset is not determined by the critical strain rate, contrary to conventional brittle fragmentation criteria widely used in volcanology. These results will help improve brittle‐ductile transition models for complex fluids in volcanic eruptions. Key Points Rapid air injection generated brittle fracture in a Maxwell fluid but not in a Bingham fluid, although they have similar elasticity The observation of elasticity in small‐amplitude oscillation tests is not sufficient to infer that the fluid can fracture The strain rate around a bubble decreased toward fracture, contrary to the conventional critical strain‐rate fracture criterion

A high-entropy dual-phase AlTiVCoNi alloy with a low density of ∼6.24 g cm −3 is developed, and it consists of a hierarchical structure, including an ordered L2 1 phase, a disordered body-centered-cubic (BCC) solid-solution phase, and nano-sized L2 1 precipitates embedded in the BCC phase. It is found that this new alloy shows phase stability after the heat treatment at 1200°C for 24 h, and the compressive yield strength of this annealed alloy is approximately equal to that of the as-cast condition, ∼1.6 GPa. This alloy displays an exceptional compressive strength at room temperature and at 600°C, with the specific yield strengths of ∼261 and ∼210 MPa g −1 cm 3 , respectively. The semi-coherent interface of the L2 1 and the BCC phases makes the alloy phase stable and regulates the work-hardening mechanism. Local dynamic-recrystallization behavior and grain evolution are observed in the as-prepared alloy during compression at 800 and 1000°C, which results in the high-temperature softening. This alloy with a muti-phase hierarchical structure would provide a new paradigm for the development of next-generation low-density, high-entropy structural materials for high-temperature applications.

Aluminum Alloy 2024/Boron carbide (B 4 C)/alumina composites showed different tensile characteristics after they were strengthened and heated. The T6 thermal cycle performance got better because the samples were made harder through “precipitation hardening” using various amounts of alumina and B 4 C. After the application of heat, the composite materials had a consistent spread of strengthening elements, and an examination of their energy levels showed Aluminum, Silicon, and Magnesium, along with small amounts of a few other particles. Researchers carefully tested the tensile properties of heat-treated and strengthened steel. The research indicated that both the tensile strength (TS) and yield strength (YS) increased to 210ºC and then started to decrease to 140ºC. The stiffness and elastic modulus of the composites improved due to the addition of reinforcement and heat treatment. This resulted in a significant reduction in El (Elongation) content in the composites. Several factors, such as the diffusion process, grain refinement, heat treatment temperatures, and the mix of strengthening elements, contributed to the enhanced elastic modulus and tensile strength of the composites. Research aimed at optimizing these findings to streamline the development of hybridized composite materials has many applications in the aerospace and transportation industries.

So far, the influence of aging on the mechanical properties of ZnAlCu alloys has primarily been investigated under tensile load. Since some applications, such as plain bearings, are subjected to compressive loads, the results presented in the literature do not fully encompass all areas of application. Therefore, this publication focuses on the influence of artificial aging on the 0.2% compressive yield strength. Samples from ZnAl1Cu0.7, ZnAl11Cu0.7 and ZnAl11Cu2 were aged at different aging temperatures for up to 840 h. After different aging periods, compressive tests as well as microstructure investigations with SEM and XRD were carried out. Furthermore, the dimensional stability of ZnAl11Cu0.7 was investigated in a quenching dilatometer. Shrinkage of up to 0.08%, followed by swelling, was determined. Compressive tests revealed a decrease in the 0.2% compressive yield strength across all tested alloys, most pronounced at the beginning of the aging process, reaching an approximately constant strength level after an alloy- and temperature-dependent aging period. At the end, based on the results, a possible way to determine the constant strength level and the necessary aging time to reach this strength level for specific application temperatures is presented to ensure stable mechanical properties during operation.

Six large-scale reinforced concrete T-shaped slender walls were tested under reversed cyclic loading to study the effects of reinforcing bar mechanical properties on wall deformation capacity. Effects on lateral stifiness and hysteretic energy dissipation were also quantified. Primary variables included reinforcement yield stress and the ratio of tensile-to-yield strength ([f.sub.t]/[f.sub.y]). An additional aim of the tests was to determine the minimum uniform elongation (strain at peak stress) and fracture elongation required of highstrength reinforcing bars for use in earthquake-resistant structures. The walls were not subjected to axial loads other than the weight of the loading apparatus and self-weight. The T-shaped walls, with a specified concrete compressive strength of 8 ksi (55 MPa), had a 100 in. (2540 mm) long stem joining a single 100 in. (2540 mm) long fange, both 10 in. (254 mm) thick. All walls had a nominal shear span of 300 in. (7620 mm). The control specimen T1 was constructed with conventional Grade 60 (420) reinforcement (where Grade corresponds to the specified yield stress of reinforcement). Walls T2, T3, T4, and T6 were constructed with Grade 100 (690) reinforcement and T5 with Grade 120 (830) reinforcement. Test results showed that regardless of the reinforcement grade, walls designed for similar flexural strength using longitudinal reinforcement with [f.sub.t]/[f.sub.y] between 1.18 and 1.39, uniform elongation not less than 6%, and fracture elongation not less than 10% had similar strengths and drift ratio capacities. The effective initial stifiness and hysteretic energy dissipation index for walls with high-strength reinforcement (T2 through T6) were approximately 70%, on average, of those for the wall with conventional reinforcement (T1). Keywords: deformation capacity; fracture elongation; high-strength reinforcement; reversed cyclic load; slender walls; tensile-to-yield strength ratio; uniform elongation.

The NbTiAlZrHfTaMoW refractory high-entropy alloy (RHEA) system with the structure of the B2 matrix (antiphase domains) and antiphase domain boundaries was firstly developed. We conducted the mechanical properties of the RHEAs at 298 K, 1023 K, 1123 K, and 1223 K, as well as typical deformation characteristics. The RHEAs with low density (7.41~7.51 g/cm3) have excellent compressive-specific yield strength (σYS/ρ) at 1023 K (~131 MPa·cm3/g) and 1123 K (~104.2 MPa·cm3/g), respectively, which are far superior to most typical RHEAs. And, they still keep appropriate plastic deformability at room temperature (ε > 0.35). The superior specific yield strengths are mainly attributed to the solid solution strengthening induced by the Zr element. The formation of the dislocation slip bands with [111](101_) and [111](112_) directions and their interaction provide considerable plastic deformation capability. Meanwhile, dynamic recrystallization and dislocation annihilation accelerate the continuous softening after yielding at 1123 K.

High-entropy alloys (HEAs) have attracted significant attention due to their exceptional physical, chemical, and mechanical properties. The current development of HEAs primarily depends on time-consuming and costly trial-and-error approaches, which not only hinder the efficient exploration of new compositions but also result in unnecessary resource and energy consumption, thereby negatively affecting sustainable development and production. To address this challenge, this study introduces a machine learning-based methodology for predicting the yield strengths of various HEA compositions. The model was trained using 181 data points and achieved an R2 performance score of 0.85. To further assess its reliability and generalization capability, the model was validated using external data not included in the collected dataset. The validation was performed across four categories: modified Cantor alloys, refractory HEAs, eutectic HEAs, and other HEAs. The predicted yield strength trends were found to align with the actual experimental trends, demonstrating the model’s robust performance across various categories of HEAs. The proposed machine learning approach is expected to facilitate the combinatorial design of HEAs, thereby enabling efficient optimization of compositions and accelerating the development of novel alloys. Moreover, it has the potential to serve as a guideline for sustainable alloy design and environmentally conscious production in future HEA development.

To ensure the stability of interior beam-column joints under seismic loads, various influencing factors are incorporated into current design criteria in different countries. However, the design concepts and the influencing factors reflected in each country are different. The bond characteristics of beam longitudinal rebar penetrated the joint are mainly influenced by the compressive strength of concrete and are presented in the form of average bond stress. In Part I, the effect of concrete compressive strength on the bond characteristics of beam longitudinal rebar was directly investigated through a bond test that directly simulated the stress state of the joint. In this study, factors affecting the bond strength and required column depth were proposed by considering the bond characteristics based on the column axial force ratio and the yield strength of the beam longitudinal rebar. The experiment involved producing 14 test specimens and performing cyclic loading, taking each variable into consideration. Based on the experimental results, the proposed equation for the effect of column axial force ratio on the bond strength showed an excellent prediction performance compared to the current design equation with a coefficient of variation of 30.7%. In addition, a bond stress equation that reflects the stress difference of the beam longitudinal rebar was proposed using the strain values measured at both ends of the joint.

Using the quenching process to create a specific residual stress distribution in steel parts is a key method for improving their strength. Although finite element simulation can overcome the time-consuming and labor-intensive limitations of experimental measurements, accurately predicting the residual stress distribution in quenched steel parts remains a challenge for researchers and manufacturers. The initial yield strength weighting scheme used in finite element simulations has a significant impact on the results. To investigate the influence of initial yield strength weighting on the residual stress distribution in quenched steel cylinders, finite element models with different yield strength weightings have been developed. The results show that the large hardness difference between austenite and martensite can cause significant deviations between the residual stress predicted using linear weighting and the experimental results. The linear weighting scheme commonly used by researchers overestimates the yield strength of the austenite phase in the mixed-phase material during cooling, leading to an overestimation of residual stress. Employing nonlinear yield strength weightings, such as Leblond weighting, can significantly improve the computational accuracy of finite element models, yielding more reliable and consistent predictions. This improved accuracy in predicting residual stress using finite element simulation offers a powerful tool for optimizing the quenching process.

HY-80 and HY-100 steels, widely used in constructing large ocean vessels and submarine hulls, contain mixed microstructures of tempered bainite and martensite and provide high tensile strength and toughness. Weld integrity in HY steels has been studied to verify and optimize welding conditions. In this study, the T-joint weld coupons, HY80 and HY100, were fabricated from HY-80 and HY-100 steel plates with a thickness of 30 mm as base metals by submerged-arc welding. Flux-cored arc welding was performed on an additional welding coupon consisting of HY-100 to evaluate the effect of repair welds (HY100RP). Microstructures in the heat-affected zones (HAZ) were thoroughly analyzed by optical observation. Instrumented indentation testing, taking advantage of local characterization, was applied to assess the yield strength and the residual stress of the HAZ and base regions. The maximum hardness over 400 HV was found in the HAZ due to the high volume fraction of untempered martensite microstructure. The yield strength of the weld coupons was evaluated by indentation testing, and the results showed good agreement with the uniaxial tensile test (within 10% range). The three coupons showed similar indentation residual stress profiles on the top and bottom surfaces. The stress distribution of the HY100 coupon was comparable to the results from X-ray diffraction. HY100RP demonstrated increased tensile residual stress compared to the as-welded coupon due to the effect of the repair weld (323 and 103 MPa on the top and bottom surfaces). This study verifies the wide applicability of indentation testing in evaluating yield strength and residual stress.