The onset of plasticity in quenched martensitic microstructures is characterized by a low initial yield stress, extreme initial hardening, and sudden saturation. The existing literature attributes ...these phenomena to residual stresses or microstructural heterogeneities. We introduce a novel perspective, suggesting that orientation-dependent yielding of lath martensite, induced by inter-lath sliding, significantly contributes to the observed behavior. To support this, we employ a numerical microstructural model, considering the yielding anisotropy of martensite packets due to sliding along their habit plane orientation. The combined response of early yielding in martensite packets with a favorable habit plane, along with those initially remaining elastic due to an unfavorable orientation, results in a macro-scale behavior with a low initial yield stress, followed by substantial initial hardening until the saturation stress level is approached. The simulations also qualitatively capture other observations reported for quenched martensitic steels, e.g. the effect of carbon content.
Engineered Cementitious Composite (ECC) is an advanced fiber-reinforced concrete exhibiting multiple-cracking and strain-hardening under tension. This study aims to explore the feasibility of ...producing high-strength seawater sea-sand Engineered Cementitious Composites (SS-ECC) for marine and coastal applications facing the shortage of freshwater and river/manufactured sand. The effects of key composition parameters including the sea-sand size (1.18/2.36/4.75 mm), the polyethylene fiber length (6/12/18 mm), and the fiber volume dosage (1.0/1.5/2.0%) on the mechanical performance of SS-ECC were comprehensively investigated. SS-ECC with tensile strength over 8 MPa, ultimate tensile strain about 5%, and compressive strength over 130 MPa were achieved. Using seawater and sea-sand had almost no negative effects on the 28-day mechanical properties of high-strength ECC. For SS-ECC, increasing fiber length and dosage enhanced the tensile strain capacity, and sea-sand size had limited effects on the tensile performance; these phenomena were interpreted by the micromechanical analysis. A probabilistic-based method was proposed to analyze the reliability of the tensile strain capacity of SS-ECC, and it showed good agreement with the experimental results. The findings provide new insights into the design and applications of ECC in marine and coastal infrastructures for improving safety, durability, sustainability, and reliability.
•SS-ECC with compressive strength >130 MPa for marine and coastal applications was developed.•High-strength SS-ECC achieved tensile strength >8 MPa and tensile strain capacity about 5% at 28 days.•Using seawater had almost no negative effects on the 28-day mechanical properties of high-strength ECC.•The effects of sea-sand size, fiber length and fiber dosage on mechanical properties were investigated.•A probabilistic-based model was proposed to analyze the reliability of tensile strain capacity of ECC.
This paper presents a numerical study on the hopper discharging of widely polydisperse particles. It focuses on the effects of particle size distributions (PSDs) in the form of the log-normal ...distribution of the number (nPSD) and volume (vPSD) of particle constituents. In doing so, a recent GPU-DEM model suitable for large-scale simulations is adopted. The numerical results show that the mass discharge rate reduces with increasing nPSD spread but becomes larger at a wider vPSD spread. The discharging process is analyzed in terms of packing density, coordination number, velocities, and force network. It is observed that the packing density equally increases for both PSDs as the spread grows, whereas the coordination of the mixture reduces. Thus, a negative correlation between coordination and packing density is consistently observed. With increasing nPSD spread, the particle vertical velocities drop significantly, which are nearly unchanged for wider vPSDs. The particle-scale analysis is also extended to energy dissipation. The analysis reveals that the effect of PSD on the mass discharge rate is mainly attributed to the relative importance of different energy dissipation mechanisms. Irrespective of PSD type, the friction energy dissipation decreases with widening PSD, which becomes more pronounced near the outlet. In contrast, as the spread becomes wider, the collision dissipation near the outlet turns more important for nPSD but decreases for vPSD. These results account for different trends of discharge rates with respect to PSD type.
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•Industry relevant polydisperse particle systems are studied by a GPU-DEM model.•The discharge rate shows opposite trends with volume- and number-based PSDs.•Particle-scale dynamics and energy dissipations are comprehensively analyzed.•The local shift of energy dissipation mechanisms explains the discharge behavior.
In this paper, the influence of the Coefficient of Thermal Expansion (CTE) on the thermal stress analysis of laminated composite plates is explored. By introducing the undetermined integral terms in ...the displacement field, a new simple and efficient higher-order shear deformation theory is formulated for the thermo-mechanical behavior of thick laminated composite plates. This formulation aims to reduce the number of generated unknowns. Typically, a reduced order of the governing partial differential equations is expressed using the principle of virtual displacements. By using Navier’s technique, closed-form solutions are derived for laminated composite plates under thermal and/or mechanical loading. Unfortunately, several traditional research investigations significantly depend on the rule of the mixture to determine reliable CTE for composites. This paper offers and examines a variety of analytical micromechanics-based models for estimating CTE in laminated composite materials, incorporating into consideration different considerations. The obtained results are compared to those given by other alternative plate theories, and the efficiency and accuracy of the present theory are demonstrated for the thermomechanical behavior of laminated composite plates. This study reviews and applies several micromechanics-based models, contrary to previous investigations. Laminated composite plates could delaminate or crack due to the matrix material's longitudinal CTE, affecting fiber volume fraction and stacking sequence. Micromechanics-based approaches are important when arbitrary thermo-mechanical characteristics can generate inaccuracies. Interestingly, micromechanics-based models can estimate effective CTE. Schapery, Chamberlain, and Chamis provide models with identical longitudinal CTE. For increasing fiber volume fractions, Chamberlain's model is more sensitive to increasing fiber volume fractions. Mechanical stress changes laminated plate behavior more than thermal loading. Although all presented micromechanical-based models have simplified representations, this research attempts to provide a standard for future investigations. The use of detailed micromechanical-based models stimulates further progress in understanding and utilizing complex composite plates.
Carbonated MgO-based Engineered Cementitious Composite (ECC) has ultrahigh tensile ductility and tight crack width control behavior. However, the expectation of improved fire-resistant has not been ...confirmed. This study explored the alterations to mechanical and microstructure characteristics of this material after exposure to temperatures up to 500 °C. Material mass loss, compressive strength, tensile strength, strain capacity, and matrix fracture toughness were measured. Scanning electron microscopy, mercury intrusion porosimetry, thermogravimetric analysis, and X-ray diffraction were used to probe the degradation of the cement matrix and fibers. The effect of elevated temperature on carbonated MgO-based ECC was further assessed via examination of the micromechanical behavior of the fiber-matrix. The objective of this research was to assess the performance of carbonated MgO-based ECC exposed to fire hazards. The tensile ductility of carbonated MgO-based ECC was found to be enhanced when exposed to ∼100 °C as compared with those at room temperature ∼20 °C. Further increase in exposure temperature, however, posed a negative impact on the composite compressive strength, ultimate tensile strength, and ability to control crack width. The results provide a useful database for further investigations into carbonated MgO-based ECC for fire safety enhancement.
The mechanical properties of cement-based materials with different moisture contents are very sensitive to temperature. It is well known that engineered/strain-hardening cementitious composites ...(ECC/SHCC) are a high ductility cementitious composite material. The current research on SHCC is limited to room temperature and high temperature, and there is still a gap in the research on negative temperature. This study aims to explore the mechanisms of compressive strength and tensile properties of SHCC serving in cold environments. The effects of key parameters such as temperature (20 °C, −20 °C, −40 °C, and −60 °C) and moisture content (0%, 50%, 80%, and 100%) on the properties of SHCC were investigated comprehensively. With decreasing temperature and increasing moisture content, the compressive and tensile strengths of SHCC increased, while the tensile strain capacity decreased significantly. However, the tensile strain capacity of SHCC is still greater than 2% even at −60 °C. Micromechanical model parameters were obtained by fracture toughness and single fiber pullout tests, and the Pseudo Strain Hardening Behavior (PSH) criterion was calculated to explain the strain properties deterioration of SHCC at negative temperatures. Reliability prediction of the tensile strain capacity of SHCC at negative temperatures was made based on the Weibull distribution. The predicted results agree well with the experimental results. The predicted method can guide the design and engineering applications of SHCC in severe cold environments.
•Assessment of compressive strength and tensile properties of SHCC at negative temperatures.•Micromechanical mechanism on deterioration of tensile strain capacity of SHCC at negative temperature.•Reliability prediction of the tensile strain capacity of SHCC at negative temperatures.
This work performed stress predictions of unidirectional fiber-reinforced ceramic matrix composites (CMCs) subjected to longitudinal tension using a hierarchical quadrature element method (HQEM). The ...HQEM is a p-version finite element method that can present highly accurate results using only a few sampling points. Parametric analysis was conducted to investigate the sensitivity of the HQEM model to interface properties and the detailed process of determining the optimal interface parameters for micromechanical analysis of damaged CMCs has been elaborated. By comparison with the analytical results based on the classical shear-lag model which is commonly adopted to analyze the stress distributions of the damaged fiber-reinforced CMCs, the HQEM estimates of fiber and matrix stress distributions were validated. For uniformly loaded SiCf/SiC composites with a single matrix crack, the micromechanical behaviors of three typical cases during failure process, namely, interface perfectly bonded, interface debonding and fiber failure were analyzed, illustrating the characteristics of CMC failure and providing insight into the mechanisms relating the microstructural behavior to global failure. The present work offers the foundations of the extension of a promising approach for highly accurate and efficient fracture analysis of CMCs.
Predicting the nonlinear mechanical response of short fiber reinforced composites (SFRCs) is a crucial and challenging task. In this paper, a computationally efficient multi-scale strategy is ...proposed to predict the anisotropic elasto-plastic behavior of SFRCs using the intrinsic mechanical behavior of the pure polymer and fibers without the requirements for reverse engineering. In doing so, different simple unit cells are first examined to find the one that can adequately describe the nonlinear mechanical response of SFRCs' representative volume elements (RVE) with aligned fibers. Considering the effects of packing configuration, fiber aspect ratio, volume fraction and material properties, the performance of different unit cells is investigated. Then, the homogenized mechanical responses of unit cells are linked to Hill's anisotropic plasticity model to correlate the mechanical response of the suggested unit cell to the continuum domain. Using the pseudo-grain approach and a numerical orientation averaging framework, the effects of fiber misalignment are taken into account. A multi-step homogenization strategy is also employed to consider the variation of fiber orientation tensor and volume fraction through the thickness. Finally, the validity and robustness of the proposed multi-scale strategy are extensively investigated based on the RVE-generated results and the available experimental observations.
•Mechanical relationships between macro- and microparameters were deduced.•Rutting simulation and test of Hamburg pavement was conducted.•Burgers parameters of asphalt at different temperatures were ...Obtained by creep tests.•Distribution and transmission mechanism of contact force in rutting were revealed.
The macrorutting phenomenon of asphalt pavement is intrinsically related to the micromechanical characteristics of asphalt mixtures. In addition, changes in temperature and the repeated action of vehicles keep the pavement in a complex service state. Based on the discrete element method, this paper conducted a virtual rutting test of Hamburg pavement to capture the micromechanical evolution mechanism of rutting under complex temperature–stress coupling. Burgers and linear constitutive models were adopted to describe the viscoelastic and linear properties of mastic and aggregates, respectively. The transformation relationships between macro- and microparameters were deduced based on mechanical theory, and the macroparameters at different temperatures were determined through a creep test. To improve the calculation efficiency, the static load equivalent and time temperature equivalent principles were adopted to simulate pavement rutting, which was verified by laboratory rutting tests. In addition, the movements of coarse aggregates and the contact forces within the mixture were statistically analyzed under different loading times, temperatures and tire pressures. The results showed that the virtual rutting test can accurately predict the permanent deformation of pavement under a complex temperature–stress coupling field. The mechanical response analysis demonstrated the load distribution and transfer mechanism within the pavement and clearly explained the evolution process of rutting from the perspective of micromechanical views. Moreover, the influence law of parameters on rutting performance was illustrated using micro discrete mechanical theory.
