h i g h l i g h t s Phosphate solution is used to treat recycled concrete aggregate (RCA). Hydrox... more h i g h l i g h t s Phosphate solution is used to treat recycled concrete aggregate (RCA). Hydroxyapatite is produced by the treatment, consolidating the porous mortar layer of the RCA. Microstructure and quality of RCA are significantly improved by the treatment. The compressive strength of the concrete using RCA has been improved up to 19% by the proposed treatment.
Due to their many advantages, adhesively bonded joints are widely used to join components in comp... more Due to their many advantages, adhesively bonded joints are widely used to join components in composite structures. However, premature failure due to debonding and peeling of the joint is the major concern for this technique. Existing analytical models suffer from two major drawbacks: 1) not satisfying zero-shear stress boundary conditions at the adhesive layer's free edges [1] and 2) failure to distinguish the peel stress along two adherend/adhesive interfaces [2]. In this study, we develop a novel three parameter elastic foundation (3PEF) model to analyze a representative adhesively bonded joint, the symmetric double-lap joint, which is believed to have relatively low peel stresses. Explicit closed-form expressions of shear and peel stresses along two adhesive/adherend interfaces are yielded. This new model overcomes the existing model's major drawbacks by satisfying all boundary conditions and predicting various peeling stresses along two adherend/adhesive interfaces. It not only reaches excellent agreement with existing solutions and numerical results based on finite element analysis but also correctly predicts the failure mode of an experimentally tested double-lap joint. This new model therefore reveals the peel stresses' significant role in the failure of the double-lap joint, but the classical 2PEF model cannot create it.
Composites Part A: Applied Science and Manufacturing, 2017
This study demonstrates the ability of functionalized chopped carbon fibers (CCFs) chosen from in... more This study demonstrates the ability of functionalized chopped carbon fibers (CCFs) chosen from industrial waste to improve the thermo-mechanical properties of CCFs/epoxy composites. The defect sites onto the CCFs were created by their oxidation and the oxidized CCFs were covalently linked with siloxane functional groups to conceal their defects. The surface functionalization of CCFs was characterized by a simple chemical route, FTIR and TGA analysis, respectively. The surface morphology of functionalized CCFs showed the generation of highly dense networked globules. Epoxy composites filled with 0.5 wt % of siloxane attached CCFs (S-CCFs) showed a tremendous enhancement in storage modulus (~ 376%) without sacrificing their thermal stability. Furthermore, the S-CCFs reinforced epoxy composites demonstrate a significant improvement in the tensile and fracture properties. Such enhancement in the mechanical properties can open up the scope for the utilization of CCFs as a potential cost-effective candidate for highperformance next generation structural composites.
Adhesively bonded joints with functionally graded (FG) adherends are of practical significance si... more Adhesively bonded joints with functionally graded (FG) adherends are of practical significance since tailoring material composition through the adherend thickness can lead to more uniform shear or peeling stress distributions in the adherends and the adhesive layer near the edges of the joint. Stresses at the free edges of the adhesive layer have been found to be critical to the integrity of the joint. To this end, an analytical model is proposed for an adhesively bonded single lap joint with FG adherends. In this model, the adhesive layer is modeled as a three parameter, elastic foundation, allowing for different peel stress values at the two adherend-adhesive interfaces. Closed-form expressions for interface stresses and internal forces in the adherends are obtained. The model is validated by its agreement with finite element analysis simulations. This model shows that the peel stresses are critical at the left edge of the upper adherend-adhesive interface and at the right edge of the lower adherend-adhesive interface, suggesting that the joint is vulnerable to delaminations along the upper adherend-adhesive interface at the left edge and along the lower adherend-adhesive interface at the right edge. Parametric studies reveal the effects of adhesive thickness, adhesive stiffness, and FGM configuration on the stresses within the single lap joint. Results show that stress concentrations can be reduced near the edges of the joint by increasing the thickness of the adhesive layer, reducing the Young's modulus of the adhesive layer, and/or configuring the FG adherends so that the stiffer material is nearest the adhesive layer.
Pile foundations supporting offshore and coastal structures are usually simultaneously subjected ... more Pile foundations supporting offshore and coastal structures are usually simultaneously subjected to vertical loading from the superstructures and lateral loading due to wind or wave actions. An analytical model is presented to investigate the effects of vertical loads on the lateral responses of piles applied in such cases. In this model, the response of the soil is given by the fundamental Mindlin's solution for half-space subjected to both concentrated horizontal and vertical loads. The deformations and reaction pressures of the pile are represented by finite series. The responses of the pile are determined by using the principle of minimum potential energy. The proposed model is validated by comparison with the results of field load tests and laboratory load tests. The influence of related parameters including lateral load level, ratio of the vertical to the horizontal loads, pile slenderness ratio and pile flexibility factor has also been studied in this paper.
44th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2003
An engineering approach for evaluating the shear-mode (Mode-II) fracture toughness of bi-material... more An engineering approach for evaluating the shear-mode (Mode-II) fracture toughness of bi-material bonded interfaces is presented. A tapered beam on elastic foundation model (TBEF) is developed to analyze and design a linear Tapered End-Notched Flexure (TENF) specimen for fracture tests of bonded interfaces. The TBEF model is verified numerically by finite element analysis and experimentally by compliance calibration tests, which demonstrate that the present model can accurately predict the compliance and compliance ratechange of the specimen, and with proper design, an approximate constant rate of compliance change with respect to crack length can be achieved. The proposed TENF specimen can be used for Mode-II fracture toughness evaluations with reasonable confidence in the linearity of compliance crack-length relationship. Simplified design guideline for the TENF specimen is correspondingly developed. As an application, the fracture of wood-wood and wood-composite bonded interfaces under Mode-II loading is experimentally evaluated using the proposed TENF specimen, and the corresponding values of critical strain energy release rate are obtained. The modeling technique and testing method presented can be efficiently used for characterization of Mode-II fracture of bonded bimaterial interfaces.
h i g h l i g h t s Phosphate solution is used to treat recycled concrete aggregate (RCA). Hydrox... more h i g h l i g h t s Phosphate solution is used to treat recycled concrete aggregate (RCA). Hydroxyapatite is produced by the treatment, consolidating the porous mortar layer of the RCA. Microstructure and quality of RCA are significantly improved by the treatment. The compressive strength of the concrete using RCA has been improved up to 19% by the proposed treatment.
Due to their many advantages, adhesively bonded joints are widely used to join components in comp... more Due to their many advantages, adhesively bonded joints are widely used to join components in composite structures. However, premature failure due to debonding and peeling of the joint is the major concern for this technique. Existing analytical models suffer from two major drawbacks: 1) not satisfying zero-shear stress boundary conditions at the adhesive layer's free edges [1] and 2) failure to distinguish the peel stress along two adherend/adhesive interfaces [2]. In this study, we develop a novel three parameter elastic foundation (3PEF) model to analyze a representative adhesively bonded joint, the symmetric double-lap joint, which is believed to have relatively low peel stresses. Explicit closed-form expressions of shear and peel stresses along two adhesive/adherend interfaces are yielded. This new model overcomes the existing model's major drawbacks by satisfying all boundary conditions and predicting various peeling stresses along two adherend/adhesive interfaces. It not only reaches excellent agreement with existing solutions and numerical results based on finite element analysis but also correctly predicts the failure mode of an experimentally tested double-lap joint. This new model therefore reveals the peel stresses' significant role in the failure of the double-lap joint, but the classical 2PEF model cannot create it.
Composites Part A: Applied Science and Manufacturing, 2017
This study demonstrates the ability of functionalized chopped carbon fibers (CCFs) chosen from in... more This study demonstrates the ability of functionalized chopped carbon fibers (CCFs) chosen from industrial waste to improve the thermo-mechanical properties of CCFs/epoxy composites. The defect sites onto the CCFs were created by their oxidation and the oxidized CCFs were covalently linked with siloxane functional groups to conceal their defects. The surface functionalization of CCFs was characterized by a simple chemical route, FTIR and TGA analysis, respectively. The surface morphology of functionalized CCFs showed the generation of highly dense networked globules. Epoxy composites filled with 0.5 wt % of siloxane attached CCFs (S-CCFs) showed a tremendous enhancement in storage modulus (~ 376%) without sacrificing their thermal stability. Furthermore, the S-CCFs reinforced epoxy composites demonstrate a significant improvement in the tensile and fracture properties. Such enhancement in the mechanical properties can open up the scope for the utilization of CCFs as a potential cost-effective candidate for highperformance next generation structural composites.
Adhesively bonded joints with functionally graded (FG) adherends are of practical significance si... more Adhesively bonded joints with functionally graded (FG) adherends are of practical significance since tailoring material composition through the adherend thickness can lead to more uniform shear or peeling stress distributions in the adherends and the adhesive layer near the edges of the joint. Stresses at the free edges of the adhesive layer have been found to be critical to the integrity of the joint. To this end, an analytical model is proposed for an adhesively bonded single lap joint with FG adherends. In this model, the adhesive layer is modeled as a three parameter, elastic foundation, allowing for different peel stress values at the two adherend-adhesive interfaces. Closed-form expressions for interface stresses and internal forces in the adherends are obtained. The model is validated by its agreement with finite element analysis simulations. This model shows that the peel stresses are critical at the left edge of the upper adherend-adhesive interface and at the right edge of the lower adherend-adhesive interface, suggesting that the joint is vulnerable to delaminations along the upper adherend-adhesive interface at the left edge and along the lower adherend-adhesive interface at the right edge. Parametric studies reveal the effects of adhesive thickness, adhesive stiffness, and FGM configuration on the stresses within the single lap joint. Results show that stress concentrations can be reduced near the edges of the joint by increasing the thickness of the adhesive layer, reducing the Young's modulus of the adhesive layer, and/or configuring the FG adherends so that the stiffer material is nearest the adhesive layer.
Pile foundations supporting offshore and coastal structures are usually simultaneously subjected ... more Pile foundations supporting offshore and coastal structures are usually simultaneously subjected to vertical loading from the superstructures and lateral loading due to wind or wave actions. An analytical model is presented to investigate the effects of vertical loads on the lateral responses of piles applied in such cases. In this model, the response of the soil is given by the fundamental Mindlin's solution for half-space subjected to both concentrated horizontal and vertical loads. The deformations and reaction pressures of the pile are represented by finite series. The responses of the pile are determined by using the principle of minimum potential energy. The proposed model is validated by comparison with the results of field load tests and laboratory load tests. The influence of related parameters including lateral load level, ratio of the vertical to the horizontal loads, pile slenderness ratio and pile flexibility factor has also been studied in this paper.
44th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2003
An engineering approach for evaluating the shear-mode (Mode-II) fracture toughness of bi-material... more An engineering approach for evaluating the shear-mode (Mode-II) fracture toughness of bi-material bonded interfaces is presented. A tapered beam on elastic foundation model (TBEF) is developed to analyze and design a linear Tapered End-Notched Flexure (TENF) specimen for fracture tests of bonded interfaces. The TBEF model is verified numerically by finite element analysis and experimentally by compliance calibration tests, which demonstrate that the present model can accurately predict the compliance and compliance ratechange of the specimen, and with proper design, an approximate constant rate of compliance change with respect to crack length can be achieved. The proposed TENF specimen can be used for Mode-II fracture toughness evaluations with reasonable confidence in the linearity of compliance crack-length relationship. Simplified design guideline for the TENF specimen is correspondingly developed. As an application, the fracture of wood-wood and wood-composite bonded interfaces under Mode-II loading is experimentally evaluated using the proposed TENF specimen, and the corresponding values of critical strain energy release rate are obtained. The modeling technique and testing method presented can be efficiently used for characterization of Mode-II fracture of bonded bimaterial interfaces.
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