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The elevated temperature tensile tests of the powder metallurgy (P/M) Fe−2Cu−0.5C steels at the deformation temperatures of 850~1000 ℃ and strain rates of 0.1~10.0 s−1 were carried out by Gleeble-3500 thermal simulator. The effects of deformation temperature and strain rate on the elevated temperature tensile deformation behaviors of the P/M steels were quantitatively analyzed. The fracture work of the P/M steels during the elevated temperature tensile was calculated using the stress-strain curves. The mathematical model characterizing the relationship of fracture work, deformation temperature, and strain rate was established. The Hensel-Spittel model and BP neural network model were used to establish the constitutive equation of the P/M steels to characterize the flow behaviors during the elevated temperature tensile. The predicted results of the two models were compared. The results show that the fracture work model can describe the capacity of the P/M steels to resist fracture at different deformation temperatures and strain rates. The average absolute relative error between the predicted values of Hensel-Spittel constitutive model and the experimental values is 3.16%, and the coefficient of determination is 0.9743. While the average absolute relative error and the coefficient of determination between the predicted values of BP neural network model and the experimental values are 0.17% and 0.9999, respectively, indicating that the BP neural network model has the stronger predictive capacity and can characterize the elevated temperature tensile deformation behaviors of the P/M Fe−2Cu−0.5C steels better.

With the promotion of cold recycled mixture (CRM) in cold areas and the improvement of its application layer, the enhancement of the low-temperature performance of mixtures is particularly important. The applicability of the current low-temperature bending test method to CRM is controversial. Firstly, the low-temperature crack resistance of CRM with different gradations and emulsified asphalt contents was studied by the indirect tensile (IDT) test and the semi-circular bending (SCB) test. Thereafter, the low-temperature performance evaluation index suitable for CRM was put forward. Then, the low-temperature performance of CRM with different gradations, fiber types, and contents was evaluated by using the above low-temperature evaluation index. The results show that the low-temperature performance of CRM with different gradations and emulsified asphalt contents can be distinguished by fracture work (W) and fracture energy (Gf). Not only do the test results have little variability (about 12% and 15%, respectively), but also the correlation coefficient with the new asphalt film thickness is the highest (0.8595 and 0.8939, respectively). Compared with coarse gradation (AC-25) and fine gradation (AC-13), medium-gradation (AC-20) CRM has higher low-temperature performance, and polyester fiber can significantly improve the low-temperature performance of CRM. Compared with non-fiber, the W and Gf of CRM of polyester fiber (0.3% content) can be increased by at least 42% and 30%, respectively. [ABSTRACT FROM AUTHOR]

The thermal shock resistance of alumina ceramics with a fine-crystalline structure (crystal size 5 – 40 μm) and with a layered-granular structure, as well as t-ZrO2–Cr(40 vol. %) cermet, was studied. Layered-granular ceramics consisted of randomly oriented layered granules, including alternating dense fine-crystalline layers and porous layers made of corundum microballoons. The cermet structure is represented by two interpenetrating continuous skeletons formed from chromium grains and t-ZrO2 grains. To assess the thermal shock resistance, in addition to the known criteria R0, R1 it is proposed to use new criteria R0*, R1* and the kinetic characteristic of fracture γF/γI. These criteria were compared with the thermal shock resistance determined by the number of thermal cycles to failure N of samples and by the method of local thermal shock, which determines the relative loss of crack resistance of the sample after a single thermal cycle RT. Layered-granular Al2O3-ceramics exhibit the best thermal shock resistance due to the discrete and high-energy destruction mechanism. The use of chromium in the composition of cermet made it possible to significantly increase its thermal shock resistance in comparison with the thermal shock resistance of the ceramic component due to the presence of a heat-conducting metal component. It is shown that the application of the new criteria R0* and R1* makes it possible to reliably predict the thermal shock resistance of the studied materials from the indicators N and RT. [ABSTRACT FROM AUTHOR]

Shear stress prevalence in in-situ cemented paste backfill (CPB) makes understanding mode-II fracture behaviour and properties vital for the mechanical stability of the backfill structure. This study delves into the effect of cement content on CPB's shear fracture behaviour and properties. Results reveal that higher cement content leads to notable changes in load-displacement characteristics under mode-II loading, including steeper pre-peak slopes, higher peak loads, smaller peak-load displacements, and minimal post-peak resistance. However, increased cement content does not linearly enhance fracture properties. Furthermore, this study proposed predictive models to capture the influence of cement content on the evolutive fracture properties. • Pre-peak fracture behaviour of CPB is sensitive to changes in cement content. • Post-peak resistance in CPB is subtle, regardless of cement content. • Increasing cement content nonlinearly boots mode-II fracture properties. • Predictive models are developed to capture CPB's fracture properties. [ABSTRACT FROM AUTHOR]

• Fracture energy is better obtained using load-LLD. • Fracture energy ratio of SCB load-LLD to DCT load-CMOD is relatively constant. • Fracture test's ability to distinguish between AC mixes increases with temperature. • Flexibility index (FI) was able to distinguish between AC mixes. Fracture mechanics has been widely applied to asphalt concrete (AC) materials to evaluate the cracking potential of AC pavements under traffic and thermal loadings. While AC materials behave as quasi-brittle at low temperature and high loading rate, its behavior becomes more viscous as temperature increases and/or loading rate decreases. Considerable fracture tests have been developed to capture the fracture properties of AC materials; however, fracture properties may be misinterpreted when using various fracture tests, especially in bending-mode. This would result in an erroneous characterization of AC cracking potential, which leads to a misestimate of pavement service life. The objective of this study is to investigate common fracture test methods for the AC materials, compare the fracture energies from various displacement measurements to capture true fracture property, and examine the effect of temperature on fracture energy and Flexibility Index (FI). Fracture energy from the semi-circular bending (SCB) geometry was compared to that from the disk-shaped compact tension (DCT) test. The effect of misinterpretation of test results on fracture energies was investigated. This study also suggests a proper method to capture fracture properties from the SCB test using the basic understanding of work and energy concepts in physics. The effects of test temperature on (1) fracture energy values, (2) FI, and (3) the overall ability to discriminate the cracking potential of AC mixtures are presented. Results show that while the crack characteristics can be captured more reasonably with a Load-Crack Mouth Opening Displacement (CMOD) curve, the fracture energy is better obtained using load-Load Line Displacement (LLD) curve. Moreover, performing fracture tests at a relatively higher temperature increases the ability to distinguish between various AC mixtures' cracking potential. [ABSTRACT FROM AUTHOR]

Some requirements are formulated for tool steels used to make tools with their durability being limited by strength and impact resistance rather than by wear resistance. It is shown that the high-speed steel belonging to a new hypereutectoid class is optimal for the above-mentioned application. The fracture mechanisms are considered for ledeburitic (R6M5) and hypereutectoid (11M5F) classes of tool steels. It is demonstrated that critical length crack formation in hypereutectoid steels takes place not only by means of elastic but also by means of considerable plastic deformation; on this account, the work of crack initiation in 11M5F considerably exceeds that of R6M5. The above-mentioned fact is due to the peculiarities of 11M5F steel microstructure characterized by extremely fine grain and the absence of eutectic carbides. Correlation between fracture work and deformation is established under static bending (on one hand) and impact strength (on the other hand) conditions. [ABSTRACT FROM AUTHOR]

Highlights: [•] The bitumen emulsion mortar specimen ductility reaches the maximum after approximately 28days. [•] Three months after the compaction, fracture of all the specimens was clearly brittle. [•] The evaluated energy-based parameters were substantially dependent on the viscosity of the bitumen in the emulsions. [•] The adhesion between the binder and the aggregate was assumed to emerge faster than the binder’s viscosity increased. [ABSTRACT FROM AUTHOR]

Bottom-up fatigue cracking, which is a major distress in asphalt pavements, is due to repeated traffic loading that induces tensile stress in the asphalt concrete layers. Fatigue cracks are observed as interconnected cracks in the wheelpath of asphalt pavements. Fatigue cracking can and should be addressed during both the mix design and pavement design. Therefore, a performance indicator is needed during the mix design to select a fatigue-resistant mix. In addition, a fatigue model, which includes the performance indicator, is needed to design the pavement structure. This study is conducted to determine a performance indicator for fatigue and to develop a new fatigue model, based on the Federal Highway Administration's Accelerated Load Facility experiments on fatigue. It is found that the fracture work density (FWD) obtained from indirect tensile testing correlates highly with field fatigue performance, whereas fracture energy fails to correlate with field fatigue performance. A new fatigue model based on FWD is developed herein and is found to be effective in characterising field fatigue performance. Further study is needed to validate the effectiveness of FWD and the new fatigue model. [ABSTRACT FROM AUTHOR]

The primary distresses of the asphalt pavement are rutting, fatigue cracking, and thermal cracking. Laboratory tests can be conducted to characterize the expected performance of asphalt concrete in the field. This study evaluated the double punch test (DPT) as an alternative test method to characterize the fatigue and rutting of asphalt concrete due to its simplicity. In DPT, a cylindrical asphalt concrete specimen is compressed vertically through two steel punches placed concentrically on the top and bottom. The specimen fails along the diametrical plane due to the tensile strain generated in the tangential direction. Double punch tests were performed at intermediate and high temperatures to characterize fatigue and rutting potential of asphalt concrete, respectively. The DPT results were found to correlate well with fatigue parameters from indirect tensile (IDT) tests for fatigue and flow number test results for rutting, both of which have been reported to correlate well with field fatigue and rutting performance, respectively. The results indicate that the DPT can serve as a viable alternative to evaluate the fatigue and rutting behavior of asphalt concrete. [ABSTRACT FROM AUTHOR]

Moduli of deformability, maximum stress, maximum strain and fracture work have been determined for chestnuts as functions of moisture content. Fresh and dehydrated chestnuts obtained by convective drying, as well as frozen chestnuts, have been tested. The samples were cut in prisms. Uniaxial compression tests in a Universal Testing Machine were employed. Hencky's model was selected as the most appropriate one. Dried chestnuts at 65 °C show a non-linear behaviour of the modulus of deformability and maximum stress with the moisture content under 0.25 kg kg−1 [dry basis (d.b.)], while both parameters are practically constant for upper values. The modulus of deformability and the maximum stress have been correlated with the aw, obtaining a decreasing linear behaviour below aw values around 0.82. The higher maximum strain values were found at moisture contents around 0.41 kg kg−1 (d.b.), and it stays practically constant below 0.25 kg kg−1 (d.b.). Defrosted chestnuts show lower modulus of deformability and maximum stress values, but the maximum strain values are higher. This fact reveals a lesser firmness in their structures compared with fresh fruits. [ABSTRACT FROM AUTHOR]