Fangliang Chen

On the Compliance and Energy Release Rate of Generically-unified Beam-type Fracture Specimens

A unified approach is proposed to evaluate the compliance and energy release rate (ERR) of generic beam-type interface fracture specimens. Based on a sub-layer Timoshenko beam theory, the classic composite (rigid joint), shear deformable (semi-rigid joint), and interface deformable (flexible joint) bi-layer beam models are revisited, from which the compliance and ERR of the generic beam-type fracture specimens are determined. According to specific combinations of loading conditions and material properties of each sub-layer, the generic fracture specimens are reduced to the conventional fracture specimens for actual applications. The effects of the crack tip deformation on the ERR of the interface crack are compared among the three different joint models, from which the evolving accuracy of the joint models to the ERR predictions of beam-type fracture specimens is manifested. The derived explicit formulas and improved solution for the compliance and ERR of the common beam-type fracture specimens can be eff...A unified approach is proposed to evaluate the compliance and energy release rate (ERR) of generic beam-type interface fracture specimens. Based on a sub-layer Timoshenko beam theory, the classic composite (rigid joint), shear deformable (semi-rigid joint), and interface deformable (flexible joint) bi-layer beam models are revisited, from which the compliance and ERR of the generic beam-type fracture specimens are determined. According to specific combinations of loading conditions and material properties of each sub-layer, the generic fracture specimens are reduced to the conventional fracture specimens for actual applications. The effects of the crack tip deformation on the ERR of the interface crack are compared among the three different joint models, from which the evolving accuracy of the joint models to the ERR predictions of beam-type fracture specimens is manifested. The derived explicit formulas and improved solution for the compliance and ERR of the common beam-type fracture specimens can be effectively used to reduce data in interface fracture experiments and increase accuracy of fracture toughness evaluation of dissimilar material interfaces.

Local Delamination Buckling of Laminated Composite Beams Using Novel Joint Deformation Models

Local delamination buckling formulas for laminated composite beams are derived based on the rigid, semirigid, and flexible joint models with respect to three bilayer beam (i.e., conventional composite, shear-deformable bilayer, and interface-deformable bilayer, respectively) theories. Two local delamination buckling modes (i.e., sublayer delamination buckling and symmetrical delamination buckling) are analyzed and their critical buckling loads based on the three joint models are obtained. A numerical finite-element simulation is carried out to validate the accuracy of the formulas, and parametric studies of delamination length ratio, the transverse shear effect, and the influence of interface compliance are conducted to demonstrate the improvement of the flexible joint model compared to the rigid and semirigid joint models. The explicit local delamination buckling solutions developed in this study facilitate the design analysis and optimization of laminated composite structures and provide simplified and improved practical design equations and guidelines for buckling analyses.

Mixed-Mode Fracture of Hybrid Material Bonded Interfaces under Four-Point Bending

A combined analytical and experimental approach is presented to characterize mixed-mode fracture of hybrid material bonded interfaces under four-point bending load, and closed-form solutions of compliance and energy release rate (ERR) of the mixed-mode fracture specimens are provided. The transverse shear deformations in each sublayer of bimaterial bonded beams are included by modeling the specimen as individual Timoshenko beams, and the effect of interface crack-tip deformation on the compliance and ERR are taken into account by applying the interface deformable bilayer beam theory (flexible-joint model). The higher accuracy of the present analytical solutions for both the compliance and ERR of mixed-mode fracture specimens is manifested by comparing them with the solutions predicted by the conventional beam theory (CBT) and finite-element analysis (FEA). As an application example, the fracture of wood–fiber-reinforced plastic (FRP) bonded interface is experimentally evaluated by using mixed-mode fractur...

Electromechanical Behavior of Interface Deformable Piezoelectric Bilayer Beams

An interface deformable piezoelectric bilayer beam model is proposed to study the electromechanical responses and interface stress distributions in an intelligent layered structure. Like most of current approaches in the literature, the layerwise approximation of electric potential is employed. While in contrast to the linear approximation where the induced electric field is ignored, the present model takes a quadratic variation of the potentials across the thickness, thus warranting an efficient and accurate modeling of the electric field. Completely different from the widely used equivalent single layer model, in which the whole laminate is assumed to deform as a single layer and thus has a smooth variation of the displacement field over the thickness, the present model considers each sublayer as a single linearly elastic Timoshenko beam perfectly bonded together and therefore with individual deformations. To ensure the continuity of deformations of two adjacent sublayers along the interface, two interface compliance coefficients are introduced, by which both the longitudinal and vertical displacement components along the interface of two sublayers due to the interface shear and normal stresses are taken into account. To assess the performance of the present model, a number of benchmark tests are performed for a piezoelectric bimorph and a piezoelectric-elastic bilayer beam subjected to (1) a force density normal to the upper face and (2) an electric potential applied to the top and bottom faces. A remarkable agreement achieved between the present solution and the finite element computations illustrates the validity of the present study. The present model not only predicts well the global responses (displacement, electric charge, etc.), but also provides excellent estimates of the local responses (through-thickness variations of electromechanical state, interface stress distributions, etc.) of the piezoelectric layered structures. The novel mechanics model of electroelastic layered structures presented can be used to efficiently and effectively characterize hybrid smart devices and develop/optimize new multifunctional materials.

Improved Mechanical Properties and Early-Age Shrinkage Resistance of Recycled Aggregate Concrete with Atomic Polymer Technology

To overcome some inferior physical and mechanical properties of recycled aggregate concrete (RAC), an enhancing technique is presented in this paper to improve the performance of RAC by adding a promising chemical admixture, an atomic polymer technology (APT) in the form of a mesoporous inorganic polymer (MIP). The RAC samples with different added amounts of MIP were prepared, and their mechanical and physical properties were measured. Various basic material and durability properties, such as stiffness, strength, and early-age shrinkage, were evaluated. The smart piezoelectric cement modules as either sensors or actuators were fabricated, and they were embedded in concrete beams to monitor the early-age stiffness-gaining process of the RAC samples during its curing stage. The corresponding monitoring techniques based on wave propagation were developed and implemented, through which the gradually improved performance of RAC with increasingly added amounts of MIP was evaluated and the early-age condition of RAC during its curing period were monitored in situ. The findings on the improved mechanical properties of RAC with atomic polymer technology and condition assessment from an early age with smart piezoelectric cement modules will potentially promote widespread application of recycled concrete in engineering, improve the sus- tainability of RAC structures, and provide viable health-monitoring techniques for RAC structures. DOI: 10.1061/(ASCE)MT.1943-5533 .0000759.

Local Buckling Analysis of Restrained Orthotropic Plates under Generic In-Plane Loading

AbstractAn analytical study of local buckling of discrete laminated plates or panels of fiber-reinforced plastic structural shapes is presented. Two cases of composite plate analyses with two opposite edges simply supported and the other two opposite edges either both rotationally restrained or one rotationally restrained and the other free, are studied. Generic loading cases with combined linearly varying axial and in-plane shear loading are considered. A variational formulation of the Ritz method is used to establish the eigenvalue problem for the local buckling behavior, and explicit expressions for predictions of the plate buckling stress resultants, in terms of the rotationally restrained stiffness, the plate aspect ratio, and the ratios of applied stress resultants, are developed. Based on different boundary and loading conditions, simple and explicit local buckling solutions for several special cases are further reduced. Validity of the explicit solutions presented is demonstrated by a good agreeme...

Material property assessment and crack identification of recycled concrete with embedded smart cement modules

In this paper, the material property assessment and crack identification of concrete using embedded smart cement modules are presented. Both the concrete samples with recycled aggregates (RA) and natural aggregates (NA) were prepared. The smart cement modules were fabricated and embedded in concrete beams to serve as either the actuators or sensors, and the elastic wave propagation-based technique was developed to detect the damage (crack) in the recycled aggregate concrete (RAC) beams and monitor the material degradation of RAC beams due to the freeze/thaw (F/T) conditioning cycles. The damage detection results and elastic modulus reduction monitoring data demonstrate that the proposed smart cement modules and associated damage detection and monitoring techniques are capable of identifying crack-type damage and monitoring material degradation of the RAC beams. Both the RAC and natural aggregate concrete (NAC) beams degrade with the increased F/T conditioning cycles. Though the RAC shows a lower reduction percentage of the modulus of elasticity from both the dynamic modulus and wave propagation tests at the given maximum F/T conditioning cycle (i.e., 300 in this study), the RAC tends to degrade faster after the 180 F/T cycles. As observed in this study, the material properties and degradation rate of RAC are comparable to those of NAC, thus making the RAC suitable for transportation construction. The findings in development of damage detection and health monitoring techniques using embedded smart cement modules resulted from this study promote the widespread application of recycled concrete in transportation construction and provide viable and effective health monitoring techniques for concrete structures in general.

INTERFACE STRESS DISTRIBUTION IN FRP -STRENGTHENED CONCRETE BEAMS

In this study, an improved bi -material beam theory with adhesive interface is presented to evaluate the interface stress distribut ions of a concrete beam reinforced by an externally bonded fiber -reinforced plastic (FRP) composite plate. Both the adherend normal and tangential deformations induced by interface stresses are considered by introducing two interface compliances, from whi ch an improved solution of interface stress distributions is obtained. Closed -form solutions of interface stresses are presented , and favorable agreement s between the present solutions and those of the literature for a carbon FRP strengthened concrete bea m are achieved , thus demonstrating the validity of the solutions . T he present improved bi -material beam theory provides a better prediction of t he interface stress distributions, especially for adherend materials (i.e., beam and bonded plate) made of rela tively low stiffness properties (e.g., wood material as the originally strengthened beam and thin FRP composite as the strengthening plate), and it can be used to analyze the interface debonding in the beams with externally adhesive -bonded plates.