The Experts below are selected from a list of 40071 Experts worldwide ranked by ideXlab platform
Qing Li - One of the best experts on this subject based on the ideXlab platform.
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Phase field fracture in elasto-plastic solids: a length-scale insensitive model for quasi-brittle materials
Computational Mechanics, 2020Co-Authors: Jianguang Fang, Chengqing Wu, Timon Rabczuk, Chi Wu, Qing LiAbstract:Phase-field methods for fracture have been integrated with plasticity for better describing constitutive behaviours. In most of the previous phase-field models, however, the length-scale parameter must be interpreted as a material property in order to match the material strength in experiments. This study presents a phase-field model for fracture coupled with plasticity for quasi-brittle materials with emphasis on insensitivity of the length-scale parameter. The proposed model is formulated using variational principles and implemented numerically in the finite element framework. The effective yield stress is calibrated to vary with the length-scale parameter such that the tensile strength remains the same. Moreover, semi-analytical solutions are derived to demonstrate that the length-scale parameter has a negligible effect on the stress–displacement curve. Five representative examples are considered here to validate the phase-field model for fracture in quasi-brittle materials. The simulated force–displacement curves and crack paths agree well with the corresponding experimental results. Importantly, it is found that the global structural response is insensitive to the length scale though it may influence the size of the Failure Zone. In most cases, a large length-scale parameter can be used for saving the computational cost by allowing the use of a coarse mesh. On the other hand, a sufficiently small length-scale parameter can be selected to prevent overly diffusive damage, making it possible for the proposed phase-field model to simulate the fracture behaviour with $$ \varGamma $$ Γ -convergence.
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Failure mechanisms in carbon fiber reinforced plastics cfrp aluminum al adhesive bonds subjected to low velocity transverse pre impact following by axial post tension
Composites Part B-engineering, 2019Co-Authors: Xuefei Shao, Qing LiAbstract:Abstract The present study aimed to explore the effects of impact surface and impact energy on the residual characteristics of the carbon fiber reinforced plastics (CFRP)/aluminum (Al) adhesive bonded joints. The adhesive specimens were manufactured in the hot pressing machine with specific curing temperature and curing pressure of the adhesive. In the experiments, a transverse low velocity pre-impact was carried out first and then followed by the axial (longitudinal) tensile test. The results divulged that CFRP, as an impact surface, could generate better structural integrity and decrease loss of joint strength in comparison with the aluminum impact surface. The mechanism for alternating residual tensile strength resulting from transverse impact load was the combined effect of both damage and mechanical interlocking effectiveness. The residual tensile strength and Failure displacement decreased with increasing impact energy except for the joint strength impacted onto the aluminum surface at 10 J due to the prominent mechanical interlocking effect. The strain evolution paths in the adherends at the overlap region presented the different forms when impacted onto the different surfaces. In the tensile tests, the fracture surfaces for the joints with impacting on the aluminum surface can be classified as shear Failure Zone, annular Failure Zone and mixed Failure Zone, while the fracture surfaces for the joints with impacting onto the CFRP surface classified to be shear Failure Zone and crossed impact Zone. This study is expected to provide systematic understanding on crashing behavior of adhesive joints with dissimilar materials for multiple impacts from different directions.
Li Jie - One of the best experts on this subject based on the ideXlab platform.
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In-situ strength estimation of polypropylene fibre reinforced recycled aggregate concrete using Schmidt rebound hammer and point load test
'Informa UK Limited', 2020Co-Authors: Kazemi Mostafa, Hajforoush Mohammad, Khakpour Talebi Pouyan, Daneshfar Mohammad, Shokrgozar Ali, Jahandari Soheil, Saberian Mohammad, Li JieAbstract:peer reviewedAn appropriate amount of polypropylene fibre (PF) content is generally able to compensate for the low compressive strength of the recycled aggregate concrete. This mechanical strength is required to reliably estimate at the building site using partially and non-destructive testing methods. Therefore, in the present study, the compressive strength of concrete with PF at 0.1% by volume and different replacement levels of recycled coarse aggregate (RCA) was assessed using point load test (PLT) and Schmidt rebound hammer. According to the results, the sensitivity of the core specimens to the concentrated point load and the short size of PF in the Failure Zone of the PLT caused to appear a difference among the enhancement trends of PLI values by increasing the age. In addition, a two-variable equation between the rebound number and point load index (PLI) reliably predicted either strength of coarse natural concrete or recycled aggregate concrete or PRAC
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[In Press] In-situ strength estimation of polypropylene fibre reinforced recycled aggregate concrete using Schmidt rebound hammer and point load test
U.K. Taylor & Francis, 2020Co-Authors: Kazemi Mostafa, Hajforoush Mohammad, Daneshfar Mohammad, Shokrgozar Ali, Jahandari Soheil, Saberian Mohammad, Talebi, Pouyan K., Li JieAbstract:An appropriate amount of polypropylene fibre (PF) content is generally able to compensate for the low compressive strength of the recycled aggregate concrete. This mechanical strength is required to reliably estimate at the building site using partially and non-destructive testing methods. Therefore, in the present study, the compressive strength of concrete with PF at 0.1% by volume and different replacement levels of recycled coarse aggregate (RCA) was assessed using point load test (PLT) and Schmidt rebound hammer. According to the results, the sensitivity of the core specimens to the concentrated point load and the short size of PF in the Failure Zone of the PLT caused to appear a difference among the enhancement trends of PLI values by increasing the age. In addition, a two-variable equation between the rebound number and point load index (PLI) reliably predicted either strength of coarse natural concrete or recycled aggregate concrete or PRAC
Hemanta Hazarika - One of the best experts on this subject based on the ideXlab platform.
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analyses of active earth pressure against rigid retaining wall subjected to different modes of movement
Soils and Foundations, 1996Co-Authors: Hiroshi Matsuzawa, Hemanta HazarikaAbstract:A numerical investigation was carried out to evaluate the effect of wall movement modes on static active earth pressure. Interface elements with bi-linear stress-displacement relation are newly developed and introduced between the backfill soil and the wall to simulate the frictional behavior. The conventional linkage elements have been idealized suitably to avoid separation between the wall and the soil during the active movement of the wall. The active state has been defined based on the progressive formation of a Failure Zone in the backfill. The tendency of the Failure Zone formation is seen to be governed by the modes of wall movement. The calculated active state parameters were compared with the parameters calculated using other methods based on rigid plastic assumptions. The resultant active thrusts and their points of application are found to be a function of the wall movement modes. Empirical equations containing wall movement mode as a governing parameter were derived for calculating the active earth pressure coefficient and the relative height of the resultant active thrust for various angles of internal friction of the backfill.
L J Sluys - One of the best experts on this subject based on the ideXlab platform.
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a multi scale scheme for modelling fracture under dynamic loading conditions
Key Engineering Materials, 2014Co-Authors: A Karamnejad, L J SluysAbstract:Fracture in heterogeneous materials under dynamic loading is modelled using a multi-scale method. Computational homogenization is considered, in which the overall properties at the global-scale are obtained by solving a boundary value problem for a representative volume element (RVE) assigned to each material point of the global-scale model. In order to overcome the problems with upscaling of localized deformations, a non-standard Failure Zone averaging scheme is used. Discontinuous cohesive macro-cracking is modelled using the XFEM and a gradient-enhanced damage model is used to model diffuse damage at the local-scale. A continuous-discontinuous computational homogenization method is employed to obtain the traction-separation law for macro-cracks using averaged properties calculated over the damaged Zone in the RVE. In the multi-scale model, a dynamic analysis is performed for the global-scale model and the local-scale model is solved as a quasi-static problem. Dispersion effects are then captured by accounting for the inertia forces at the local-scale model via a so-called dispersion tensor which depends on the heterogeneity of the RVE. Numerical examples are presented and the multi-scale model results are compared to direct numerical simulation results. Objectivity of the multi-scale scheme with respect to the RVE size is examined.
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on the existence of representative volumes for softening quasi brittle materials a Failure Zone averaging scheme
Computer Methods in Applied Mechanics and Engineering, 2010Co-Authors: Vinh Phu Nguyen, Oriol Lloberasvalls, Martijn Stroeven, L J SluysAbstract:The concept of the representative volume element (RVE) for softening materials is revised in this contribution. It is demonstrated by means of numerical simulations that there exists a sample which is statistically representative for quasi-brittle materials with random microstructure like concrete. This finding is an important ingredient for homogenization-based multiscale modelling of softening materials.
Kazemi Mostafa - One of the best experts on this subject based on the ideXlab platform.
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In-situ strength estimation of polypropylene fibre reinforced recycled aggregate concrete using Schmidt rebound hammer and point load test
'Informa UK Limited', 2020Co-Authors: Kazemi Mostafa, Hajforoush Mohammad, Khakpour Talebi Pouyan, Daneshfar Mohammad, Shokrgozar Ali, Jahandari Soheil, Saberian Mohammad, Li JieAbstract:peer reviewedAn appropriate amount of polypropylene fibre (PF) content is generally able to compensate for the low compressive strength of the recycled aggregate concrete. This mechanical strength is required to reliably estimate at the building site using partially and non-destructive testing methods. Therefore, in the present study, the compressive strength of concrete with PF at 0.1% by volume and different replacement levels of recycled coarse aggregate (RCA) was assessed using point load test (PLT) and Schmidt rebound hammer. According to the results, the sensitivity of the core specimens to the concentrated point load and the short size of PF in the Failure Zone of the PLT caused to appear a difference among the enhancement trends of PLI values by increasing the age. In addition, a two-variable equation between the rebound number and point load index (PLI) reliably predicted either strength of coarse natural concrete or recycled aggregate concrete or PRAC
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[In Press] In-situ strength estimation of polypropylene fibre reinforced recycled aggregate concrete using Schmidt rebound hammer and point load test
U.K. Taylor & Francis, 2020Co-Authors: Kazemi Mostafa, Hajforoush Mohammad, Daneshfar Mohammad, Shokrgozar Ali, Jahandari Soheil, Saberian Mohammad, Talebi, Pouyan K., Li JieAbstract:An appropriate amount of polypropylene fibre (PF) content is generally able to compensate for the low compressive strength of the recycled aggregate concrete. This mechanical strength is required to reliably estimate at the building site using partially and non-destructive testing methods. Therefore, in the present study, the compressive strength of concrete with PF at 0.1% by volume and different replacement levels of recycled coarse aggregate (RCA) was assessed using point load test (PLT) and Schmidt rebound hammer. According to the results, the sensitivity of the core specimens to the concentrated point load and the short size of PF in the Failure Zone of the PLT caused to appear a difference among the enhancement trends of PLI values by increasing the age. In addition, a two-variable equation between the rebound number and point load index (PLI) reliably predicted either strength of coarse natural concrete or recycled aggregate concrete or PRAC
