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Fibre reinforced concrete (FRC) exhibits complicated failure modes such as fibre breakage, mortar cracking, crushing and spalling, fibre-mortar interfacial debonding, depending on many material properties, geometric dimensions, boundary and loading conditions. Most existing numerical models are unable to reproduce these failure modes that may occur simultaneously or sequentially in a specimen, mainly due to difficulties in generating finite element meshes with a large number of randomly-oriented fibres. Herein we develop a discrete-continuum coupled finite element modelling approach for FRC materials capable of effectively simulating all the major failure modes. The continuum damaged plasticity model is used to simulate damage and fracture behaviour of the mortar, while debonding of fibre-mortar interfaces is modelled by nonlinear cohesive interfacial elements. Unique techniques are devised to generate conforming meshes between fibres and the surrounding mortar so that the randomly-oriented fibres are easily modelled. The modelling approach is validated by simulating single fibre pullout tests with different inclination angles, notched and non-notched direct tensile tests and three-point bending beam tests with randomly-distributed multiple fibres. [ABSTRACT FROM AUTHOR]

The dynamic damage and fracture behavior of concrete under compression with strain rate up to 100 s −1 is investigated by Monte Carlo simulations (MCSs) of realistic meso-scale models based on high-resolution micro-scale X-ray computed tomography (XCT) images, using the concrete damaged plasticity (CDP) model. For a given strain rate, 93 2D XCT images of a 37.2 mm concrete cube are simulated to obtain statistical results of macroscopic stress–strain curves. The predicted compressive dynamic increase factor (CDIF)–strain rate curve is in good agreement with existing experimental data and empirical curves. The effects of aggregate/void area fraction on dynamic compressive strength are also analyzed, and an augmented compressive strength-strain rate relation considering the void area fraction is proposed. A full 3D model is also simulated under various strain rates. It is found that the realistic XCT-image based meso-models with the CDP model are very promising in effectively elucidating the complicated and fundamental dynamic failure mechanisms of concrete. [ABSTRACT FROM AUTHOR]

Abstract: Ti60Cu30Ni10− x Co x (x =0, 2, and 4) alloys with high fracture strength and large compressive plasticity have been investigated. The microstructure and fracture morphologies have been studied by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The largest compressive fracture plastic strain of 32.5% with the fracture strength of 2480MPa is achieved for Ti60Cu30Ni10Co4 alloy composite. The enhanced plasticity is attributed to the addition of Co element having a positive heat of mixing with Cu element, and the retardment for the shear band propagation resulted from the dendrites, which are homogeneously distributed in the matrix. The high fracture strength of the alloys is resulted from work hardening character due to a series of dislocations in the dendrites and the unique microstructure of the Ti60Cu30Ni10Co4 alloy, i.e., the coexistence of amorphous phase, nanocrystals, and micron-scale dendrites. [Copyright &y& Elsevier]

Abstract: The microstructures and deformation behavior of Ti-based metallic powders were comprehensively investigated. It has been found that, with increasing the powder size, the phase constituent alters from pure glassy to glassy with crystalline phases (face centered cubic structured NiSnZr and hexagonal structured Ti3Sn phases). Our results suggest that the synergetic effect of the thermodynamics and kinetics determines the subsequent characteristics of the crystalline precipitations. Through comparative nanoindentation tests, it was found that the small powders exhibit more pop-in events and a larger pile-up ratio, suggesting that the plastic deformation of the metallic powders is governed by the combined effects of the free volume and the crystallization, which are determined by the cooling rate. [ABSTRACT FROM AUTHOR]

The incipient plasticity of an amorphous solid represents the onset of shear deformation, which is a stochastic progress closely related to microstructure evolution. It is well known that the cooling rate plays a crucial role in the microstructure evolution of a glass. Nevertheless, how the cooling rate affects the incipient plasticity is still unclear. In this work, the incipient plastic deformation of the amorphous phase in Cu 47.5 Zr 48 Al 4 Nb 0.5 bulk metallic glass composites (BMGCs) cast with different cooling rates is systematically studied. The incipient plasticity of the glassy matrix of the BMGCs is found to occur via a first displacement burst, the occurrence of which is more stochastic as the cooling rate decreases. According to the auto-correlation functions and cooperative shear model, the stochastic behavior is attributed to the effects of the cooling rate on the initial free volume and subsequent activated shear transformation zones (STZs). A higher content of free volume is present in the glassy matrix of the studied samples cooled at a faster rate, which facilitates the operation of STZs. Moreover, the larger incipient burst size is correlated with the higher content of free volume and larger STZs in the glassy matrix. The larger STZs result in more preferable propagation of multiple shear bands, leading to less stochastic deformation and more obvious plastic deformation. This study provides further understanding on the incipient plasticity of glassy matrix in BMGCs. Image 1 • Hardness and elastic modulus of amorphous phase are higher at a lower cooling rate. • The deformation of amorphous phase is more stochastic as cooling rate decreases. • Larger shear transformation zones facilitate the formation of multiple shear bands. • Initial free volume is the dominant role in mechanical behavior of amorphous phase. [ABSTRACT FROM AUTHOR]

Understanding the relationship between strain rate and deformation behavior in micro-sized amorphous alloys is key to optimizing mechanical properties for emerging flexible skin smart sensors and engineering applications. The tensile behavior of Co 68.15 Fe 4.35 Si 12.25 B 15.25 amorphous fiber was investigated over a wide range of strain rate of 5 × 10−5 s−1–1 × 10−1 s−1 at room temperature (RT) by an in-situ video extensometer system. Higher shear strain rate resulted in a hardening effect, thereby facilitating enhanced fracture strength. In contrast, tensile plasticity increased with decreasing strain rate. In comparison, to analyze the strain rate sensitivity, tensile behaviors of Fe 75 Si 10 B 15 amorphous fiber over different strain rates were also observed. Fracture strength and tensile plasticity were found to be insensitive to strain rate. Pronounced tensile plasticity of up to 1% was observed for Co-rich amorphous fiber at strain rates ≤1.0 × 10−4 s−1, which is attributed to the balance between the generation rate and extinction rate of free volume. The critical shear offset had a significant impact on the plastic deformation of amorphous fibers. A predictive relationship was established between tensile plasticity and measured critical shear offset for Co-rich fiber. • Strain rate sensitivity of tensile behavior for Fe- and Co-rich amorphous fibers was newly reported. • The highest fracture strength is nearly 4854 MPa at 5 × 10-2 s-1 applied strain rate. • Pronounced tensile plasticity up to 1% was observed at the strain rates below 1.0 × 10-4 s-1. • A predictive relationship was established between tensile plasticity and critical shear offset. [ABSTRACT FROM AUTHOR]

• The tensile behavior of the BMGMC was studied in-situ using neutron diffraction. • The crystalline phase yielded prior to the amorphous phase during the loading. • A redistribution of the applied stress was also observed in (110) and (200) planes. In situ neutron diffraction has been used to study the tensile deformation behaviors of a ZrTi-based bulk metallic glass matrix composites (BMGMC) at room temperature. The crystalline phase yielded prior to the amorphous phase during the tensile loading, and the glassy matrix bore more stress partition during the plastic deformation stage. A redistribution of the applied stress in dendrites occurred in the grains with an orientation of (110) and (200) during the plastic deformation. This work provides new insights into the tensile deformation mechanism of the BMGMCs at the microscopic level. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs) are considered as promising structural materials. Usually, HEAs with face-centered cubic (FCC) structure exhibit excellent ductility but low strength, while HEAs with body-centered cubic (BCC) structure indicate relatively high fracture strength and low ductility. In this paper, a new transformable FeCoCrNiMn HEA with dual FCC and BCC phases is prepared. Under tensile loading, this HEA undergoes strong strain-hardening, exhibiting low yield strength, high ultimate tensile strength and large tensile elongation. This HEA can maintain stable plastic deformation in a wide strain region with a high constant normalized strain hardening rate, which is far different from the continuous decrease of that for the famous Cantor HEA. The strong strain-hardening capability and large tensile ductility of this HEA can be attributed to the strain-induced FCC-BCC transformation. [ABSTRACT FROM AUTHOR]