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With over 6 million tons produced annually, thermoplastic elastomers (TPEs) have become ubiquitous in modern society, due to their unique combination of elasticity, toughness, and reprocessability. Nevertheless, industrial TPEs display a tradeoff between softness and strength, along with low upper service temperatures, typically ≤100 °C. This limits their utility, such as in bio-interfacial applications where supersoft deformation is required in tandem with strength, in addition to applications that require thermal stability (e.g., encapsulation of electronics, seals/joints for aeronautics, protective clothing for firefighting, and biomedical devices that can be subjected to steam sterilization). Thus, combining softness, strength, and high thermal resistance into a single versatile TPE has remained an unmet opportunity. Through de novo design and synthesis of novel norbornene-based ABA triblock copolymers, this gap is filled. Ring-opening metathesis polymerization is employed to prepare TPEs with an unprecedented combination of properties, including skin-like moduli (<100 kPa), strength competitive with commercial TPEs (>5 MPa), and upper service temperatures akin to high-performance plastics (≈260 °C). Furthermore, the materials are elastic, tough, reprocessable, and shelf stable (≥2 months) without incorporation of plasticizer. Structure-property relationships identified herein inform development of next-generation TPEs that are both biologically soft yet thermomechanically durable.
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TiAl alloys are high-temperature structural materials with excellent comprehensive properties, and their ideal service temperature range is about 700-950 °C. High-Nb containing the Ti-46Al-8Nb-2.5V alloy was subjected to hot compression and subsequent annealing at 900 °C. During hot compression, work-hardening and strain-softening occurred. The peak stresses during compression are positively correlated with the compressive strain rates and negatively correlated with the compression temperatures. The α2 phase exhibited a typical (0001)α2 basal plane texture after hot compression, while the ß0 and γ phases did not show a typical strong texture. Subsequent annealing at 900 °C of the hot-compressed samples resulted in significant phase transformations, specifically the α2 â γ and ß0 â γ phase transformations. After 30 min of annealing, the volume fraction of the α2 phase decreased from 39.0% to 4.6%. The microstructure characteristics and phase fraction after 60 min of annealing were similar to those after 30 min. According to the calculation of Miller indexes and texture evolution during annealing, the α2 â γ phase transformation did not follow the Blackburn orientation relationship. Multiple crystal-oriented α2 phases with nanoscale widths (20~100 nm) precipitate within the γ phase during the annealing process, which means the occurrence of γ â α2 phase transformation. Still, the γ â α2 phase transformation follows the Blackburn orientation relationship.
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This paper aims to evaluate the influence of relatively high service temperatures (near or beyond the glass transition temperature (Tg) of epoxy adhesive) on the flexural performance and end debonding phenomenon in near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP)-strengthened, reinforced concrete (RC) beams. To this end, an experimental program consisting of 24 beams (divided into four groups) was performed, where different parameters was combined (i.e., service temperature, steel reinforcement ratio, CFRP ratio, and concrete compressive strength). In addition, the effect of the testing temperature on the end debonding phenomenon was investigated with an analytical procedure according to fib Bulletin 90, and the predictions were compared to experimental results. Taking specimens tested at 20 °C as a reference, no considerable change was observed in the ultimate load of the specimens tested below 60 °C (being in the range of epoxy Tg), and all specimens failed by FRP rupture. On the other hand, the increase in testing temperature up to 70 and 85 °C was followed by a decrease in the capacity of the strengthened beams and a change in failure mode, moving from FRP rupture to end debonding and concrete crushing. The analytical procedure successfully predicted the occurrence of premature end debonding failure and demonstrated that the effect of temperature on the mechanical properties of materials can be a key factor when predicting the premature end debonding in a NSM joint.
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Thin T2 copper sheets with nine different thicknesses were employed in uniaxial tensile tests to investigate the influence of service temperature and thickness on their tensile properties. A total of 33 groups of tensile samples were separately tested at 20 °C, 100 °C, 150 °C, 200 °C, and 250 °C to obtain their elongation and their tensile and yield strengths. The change laws of the tensile properties of the investigated T2 copper were analyzed using different fitting functions. The main results show that both sheet thickness and temperature have an important influence on the tensile properties of T2 copper. As the sheet thickness increased, the tensile and yield strengths of the tested materials first increased rapidly, then decreased sharply, and finally stabilized. As the temperature increased, the tensile strength increased linearly while the yield strength decreased linearly. The relationships between the elongation and the sheet thickness and temperature were exponential and polynomial functions, respectively. T-t-Rm, T-t-Rel, and T-t-δ empirical formulas were proposed and established to predict the tensile properties of the investigated T2 copper sheet, and the predictive models exhibited solid accuracy.
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Calcium alginate capsules containing rejuvenators represent a promising method for asphalt concrete premaintenance, but their healing capacities under lower temperature conditions are still unknown. This paper investigated the healing performance of asphalt concrete containing calcium alginate capsules at low service temperatures. The Ca-alginate capsules were synthesized, and their morphology, compressive strength, thermal resistance, and relative oil content were evaluated. Besides, evaluations for the healing of asphalt concrete and the rejuvenator-release ratio of the capsules were determined via fracture-healing-refracture testing and Fourier-transform infrared spectrum experiments. Meanwhile, the glass transition temperature and rheological property of asphalt binder after compressive loading under different temperatures were explored via a differential scanning calorimeter and dynamic shear rheometer. The results showed that the capsules had good thermal resistance and mechanical strength. The capsules released less oil under -15, -10, and -5 °C than at 20 °C, and the healing ratios of the asphalt concrete with the capsules at -15, -10, and -5 °C were obviously lower than that at 20 °C. The released rejuvenator from the capsules could decrease the complex modulus and glass transition temperature of the asphalt binder. When compared with low service temperatures, the asphalt binder containing the capsules and serving at a high temperature has a better softening effect and low-temperature performance due to more oil being released.
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Solar harvesting systems applied to asphalt roads consist of pipes or coils installed a few centimeters below the asphalt pavement surface. They work thanks to a circulating fluid able to collect the heat coming from solar irradiation of the pavement surface and convert it into thermal gradients that can be used for electric energy supply. Specific attention must be paid to the design of the asphalt mixtures comprising the system. In this sense, the high in-service temperature rutting potential is one of the main issues to be assessed in such applications since the thermal optimization of asphalt mixes could lead to excessively deformable materials. The present study is a part of a wider research area aimed at developing an efficient asphalt solar collector. Here, a laboratory mixture-scale investigation is proposed to verify the anti-rutting potential of specific asphalt layers that were initially designed based on thermal properties only. Repeated load axial and wheel tracking tests are carried out on limestone- and steel slag-based bituminous mixtures. Overall, the tested layers were not fully able to satisfy the permanent deformation acceptance criteria; in this regard, possible improvements in terms of mix constituents and properties are ultimately addressed.
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Polyurethane adhesive and aluminum alloy were selected to make adhesive joints. Butt joints tested at different loading angles (0°, 45°, and 90°) using a modified Arcan fixture were selected to represent three stress states (normal stress, normal/shear combined stress, and shear stress, respectively). Firstly, the accelerated aging tests were carried out on the joints in a hygrothermal environment (80 °C/95% RH). The quasi-static tests were carried out at different temperatures (-40 °C, 20 °C, and 80 °C) for the joints after hygrothermal aging for different periods. The variation rules of the joints' mechanical properties and failure modes with different aging levels were studied. The results show that the failure load of the joints was obviously affected by stress state and temperature. In the low-temperature test, the failure load of the joints decreased most obviously, and the BJ was the most sensitive to temperature, indicating that the failure load decreased more with the increase of the normal stress ratio in the joint. Through macroscopic and SEM analysis of the failure section, it was found that the hydrolysis reaction of polyurethane adhesive itself and the interface failure of the joints were the main reasons for the decrease of joint strength. The failure models were established to characterize the adhesive structure with different aging levels at service temperature.
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The fretting fatigue performance of laminated, unidirectional (UD), pin-loaded, carbon fibre-reinforced polymer (CFRP) straps that can be used as bridge hanger cables was investigated at a sustained service temperature of 60 °C. The aim of this paper is to elucidate the influence of the slightly elevated service temperature on the tensile fatigue performance of CFRP straps. First, steady state thermal tests at ambient temperature and at 60 °C are presented, in order to establish the behaviour of the straps at these temperatures. These results indicated that the static tensile performance of the straps is not affected by the increase in temperature. Subsequently, nine upper stress levels (USLs) between 650 and 1400 MPa were chosen in order to establish the S-N curve at 60 °C (frequency 10 Hz; R = 0.1) and a comparison with an existing S-N curve at ambient temperature was made. In general, the straps fatigue limit was slightly decreased by temperature, up to 750 MPa USL, while, for the higher USLs, the straps performed slightly better as compared with the S-N curve at ambient temperature.
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Emerging as a new technology, carbon fiber-reinforced polymer (CFRP) has been introduced to rehabilitate and strengthen steel structures using an adhesive agent. However, the outdoor service temperature is potentially degrading to the mechanical strength of the adhesive, as well as affecting the bonding of the strengthened steel structure. Therefore, this paper aims to investigate the bond relationship of CFRP-strengthened steel plates exposed to service temperatures. Two types of experiments were conducted to determine the tensile and flexural performance of CFRP-strengthened steel plates. The experiments were designed using a Box-Behnken design (BBD) and response surface methodology (RSM) by considering three parameters: service temperature (25 °C, 45 °C and 70 °C), number of CFRP layers (one, three and five layers) and bond length (40, 80 and 120 mm). The findings show the dominant failure mode transformed from adhesion failure between steel and adhesive interfaces to adhesion failure between CFRP and adhesive interfaces as the service temperature increased. The tensile strength improved by 25.62% when the service temperature increased. Field emission scanning electron microscope (FESEM) analysis proved that the strength enhancement is due to the densification and reduction of the adhesive particle microstructure gaps through the softening effect at service temperature. However, service temperature is found to have less impact on flexural strength. Incorporating the experimental results in RSM, two quadratic equations were developed to estimate the tensile and flexural strength of CFRP-strengthened steel plates. The high coefficient of determination, R2, yields at 0.9936 and 0.9846 indicate the high reliability of the models. Hence, it can be used as an estimation tool in the design stage.
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Based on the all-atomic molecular dynamics simulation method, the tensile creep behavior of epoxy-based polymer was discussed. The physical and mechanical properties of the model were characterized, such as glass transition temperature and yield strength. The simulation results are very close to the previous simulation and experimental results, and the correctness of the model is verified. On this basis, the tensile creep behavior and free volume evolution of polymer epoxy resin at different temperatures and stress levels were studied. The model fully predicted the three classical stages of epoxy resin creep (the primary, secondary and tertiary) and the dependent behavior of epoxy resin creep on temperature and stress level at the molecular level, and the creep rate increases with the increase of temperature and stress level. It was found that with the progress of the creep process, the proportion of free volume increases gradually under high stress levels, indicating that the effect of creep behavior on the structure of epoxy resin is that the interaction between atoms becomes weaker and weaker by increasing the distance between atoms, which finally induces creep failure in the material.