Pizhong Qiao

Shanghai Jiao Tong University | SJTU · Department of Engineering Mechanics

In this paper, an element-based deep learning approach named DeepFEM for solving nonlinear partial differential equations (PDEs) in solid mechanics is developed to reduce the number of sampling points required for training the deep neural network. Shape functions are introduced into deep learning to approximate the displacement field within the ele...

Reinforced concrete (RC) has been widely used in infrastructure construction. Interfacial debonding between concrete and reinforcing bars, which is one of the most serious causes of structural failure, has always been a focus of research. In this paper, a novel deep learning-based guided wave analysis framework, termed the Priori Knowledge-based Mu...

Adequate development of the substrate-to-overlay bond is crucial in repaired concrete structures. Poorly developed bonds may facilitate crack propagation, a concern evaluated through fracture tests. However, the scarcity of fracture tests, especially for in-plane shear-type cracks (Mode II), coupled with the reliance on strength-based bond characte...

Repair and strengthening of concrete structures have become more important with the aging of existing infrastructure and the rising reconstruction costs. One of the popular and economical methods to extend the service life of concrete structures is to use bonded material overlays. The material mismatch between the substrate and overlay makes the su...

Concrete compressive strength is a most important material performance index and can reflect the quality of a concrete material. An innovative test method is proposed for monitoring the development of concrete compressive strength during the full curing period using smart piezoelectric modules (SPMs). The proposed method overcomes shortcomings of t...

The world is rich in marine resources, and the use of seawater, sea sand and coral instead of fresh water, river sand and gravel can solve problems such as the scarcity of traditional materials for marine engineering construction. Additionally, fibre-reinforced polymer (FRP) bars have demonstrated excellent corrosion resistance performance, which c...

A general finite element method is proposed for linear elastic fracture analysis of delaminated bilayer composite beams. An interface deformable bilayer beam model is adopted in modeling the virgin portions of bilayer beams, and it is capable of guaranteeing the continuity condition of internal forces at the tip of delamination because the bilayers...

A simple trigonometric series is first introduced to satisfy the longitudinal edges with the clamped-simply supported (CS) condition, while the deformation shape function along the transverse direction is uniquely constructed through a weighted combination of three kinds of trigonometric series to meet the arbitrarily elastically restrained boundar...

A general peridynamics-based framework for elastic bimaterial interface fracture analysis is established. In this frame, the formation of peridynamic interface bond force is presented for nonlocal interface modeling, and the energy release rate and mode mixity of interface cracks are computed with peridynamic model. A modified critical energy densi...

Aiming to reduce the carbon emission associated with ordinary Portland cement (OPC) based cementitious materials, this study explores a ubiquitous biomolecule, Tannic Acid (TA) to enhance the eco-efficiency of cement mortars through a pre-hydration process. To this end, a small amount of cement is first hydrated in the presence of TA. Due to multip...

The web buckling is one failure mode of web crippling for thin-walled fiber-reinforced plastic (FRP) composite beams subjected to transverse concentrated or distributed compression load from both the top and bottom bearing plates, and the web between the top and bottom flanges can be modeled as a plate with the rotationally-restrained (RR) and part...

Timely identification of collision damage, especially in aging bridges, is critical for the safety of commuters. However, there is no efficient, cost-effective, in-situ technique to serve this purpose. Wave propagation-based structural health monitoring (SHM) using piezoelectric material is a promising alternative for remote sensing. To that end, t...

This work explores a naturally occurring bio-molecule, tannic acid (TA) to functionalize the colloidal nano-silica (NS) for better performance in the silica fume (SF) blended mortars. The functionalization process is achieved via mixing the colloidal NS with TA solution for 5 min. The introduction of well-dispersed nano-silica can improve the parti...

This study explores a bioinspired, low-cost, and ubiquitous biomolecule-tannic acid (TA)-as a small-dose molecular-scale admixture to modify the nano-and micro-structures of the major hydration product of ordinary Portland cement (OPC) (e.g., calcium silicate hydrate (C-S-H)) so that the performance and eco-efficiency of the concrete can be signifi...

As a widely used structural form, doubly-curved composite shells have been applied in aviation and other engineering fields. With a refined mechanical model, structural performances can be accurately predicted to help designers choosing best geometrical and material parameters. This work introduces a novel rectangular finite element for doubly-curv...

Within the framework of the first-order shear deformation theory (FSDT), semi-analytical solutions for buckling and free vibration analysis of graphene-reinforced composite (GRC) laminated plates are presented by the means of the multi-term Kantorovich-Galerkin method. The method begins with expanding the displacements as the products of trial and...

Postbuckling behavior of stiffened laminated composite plates is investigated using a simplified spline finite strip method. The base plate and stiffeners are formulated by the first-order shear deformation plate theory and the Timoshenko beam theory, respectively. According to the compatibility condition between the base plate and stiffener, the b...

Accurate prediction of multiscale fracture process of concrete relies on modeling of concrete mesostructures. Though high-resolution yet realistic mesostructures can be obtained by CT technique, the size limitation of reconstructed mesostructures is still an outstanding task. In this paper, a novel method of generating synthetic mesostructures of c...

Based on a boundary layer theory of shell buckling, the semi-analytical solutions for nonlinear stability analysis of anisotropic laminated composite doubly-curved shells with rectangular planform subjected to lateral pressure are derived. A new shell model of arbitrary constant curvature and fibre stacking sequences but constant thickness is devel...

The freeze-thawing (F-T) action-induced evolution of shotcrete pore-structure is the potential cause of resistance degradation of chloride ion diffusion in cold regions. To study the degradation mechanisms, a combined multiscale experimental characterization and numerical modeling study is conducted, considering the pore-structure evolution charact...

Degradation of fracture resistance, which is a phenomenon encountered in shotcrete as exposed to the cold environment, can lead to structural failure. Microstructural damage induced by freeze-thaw (F-T) cycles serves as the presage to macroscopic failure processes. To reveal the fundamental mechanisms of degradation, it is crucial to characterize a...

A multistage aero-engine casing is a typical thin-walled structural component that is required to maintain a stable dynamic performance because it is a key component for transmitting thrust from an engine to a plane. However, the manufacturing and assembly processes will generate initial assembly deviation, influencing the mechanical properties of...

This study presents buckling and postbuckling analyses of an anisotropic laminated thin doubly curved panel with rectangular planform subjected to lateral pressure. The material of each layer in the panel is assumed to be linearly elastic, anisotropic and fiber-reinforced. The governing equations are obtained by using classical shell theory and von...

Damage detection is one of the most important major branches of non-destructive evaluation. In this study, a damage detection method for localization and size quantification of surface crack of concrete based on a Rayleigh wave attenuation model is proposed. A new physical Rayleigh wave attenuation model considering both the material and geometrica...

Based on the Galerkin method, a semi-analytical buckling and postbuckling solution of laminated composite plates with the boundary edges elastically-restrained against rotation is presented. The considered laminated plates are symmetric cross-ply, and they are loaded in pure in-plane shear or combined in-plane shear and compression. The four plate...

A new peridynamic bond failure model is proposed for mixed-mode crack fracture analysis in material interface and homogeneous isotropic materials, which utilize bond failure criteria presented for mixed-mode peridynamic bonds using the angle-dependent formations of critical stretch (CS) or critical energy density (CED). Then, three tests of asymmet...

It is crucial to investigate the evolution of microstructure to understand the deterioration mechanisms of shot-crete under cyclic freezing and thawing (F-T). In this study, nanoindentation and X-ray micro-CT techniques are integrated to characterize microstructural damage of shotcrete and its evolution due to F-T actions. An integrated statistical...

This paper proposes an axisymmetric ordinary state-based peridynamic model considering the thermal expansion effect for temperature-induced cracking of linear elastic solids. Both the force state and bond failure criterion of the model are built in axisymmetric domain. The direct calculation for peridynamic bond energy density of the axisymmetric m...

Thin-walled composite beam theory B-spline finite strip method A B S T R A C T Improved buckling analysis of stiffened laminated composite plates under axial compressive loads are conducted using spline finite strip method. The stiffened laminated composite plates are modeled as beam-plate structures, where the base plate and the stiffeners are for...

Semi-analytical solution for critical buckling load and nonlinear load-deflection relationship of I-section laminated composite curved beams with elastic end restraints is presented. The governing differential equations of thin-walled curved beams are derived from the principle of virtual displacement with full consideration of curvature effect. Th...

In this paper, the virtual crack closure technique (VCCT), commonly used in the numerical finite element method (FEM), is for the first time reformulated in nonlocal peridynamic theory, and a new peridynamics-based virtual crack closure technique (PD_VCCT) is proposed for the energy release rate calculation in the framework of peridynamics. The mod...

The thermo-mechanical properties of shape memory alloy hybrid composites (SMAHC) are characterized, and their three-phase constitutive relationship in the form of a lamina embedded with shape memory alloy (SMA) wires is established by micromechanics. Considering large beam deflection, a theoretical bending model of SMAHC beams with different fiber...

Nonlinear dynamic analysis for a shear deformable anisotropic laminated doubly curved panel of rectangular planform resting on elastic foundations is presented. A new panel model of arbitrary curvature and arbitrary fiber stacking sequences, but constant thickness is developed and established. The governing equations are based on an extended higher...

In this study, a fully-discrete peridynamic modeling approach is proposed to simulate tensile fracture behavior of fiber-reinforced cementitious composites. In this modeling approach, matrix is described by a peridynamic cohesive model, fibers are modeled as peridynamic bars, and fiber-matrix bond is simulated by a peridynamic interface model. The...

Ordinary state-based peridynamics (OSPD) is a promising computational method to analyze damage and fracture process because its equation of motion is still satisfied at the presence of discontinuities. Though OSPD has been introduced to evaluate mesoscopic behavior of concrete, there are many unsolved issues to tackle quasi-brittle behavior of meso...

The durability of ultra-high-performance concrete (UHPC) exposed to freezing–thawing (F–T) is closely associated with its micromechanical properties. In this study, the nanoindentation technique is employed to characterise the micromechanical properties of UHPC at different F–T cycles. It is observed that the indentation moduli of low-density calci...

The non-ordinary state-based peridynamics (NSPD) is a promising method for fracture analysis, and it can incorporate the constitutive relationship of classical continuum mechanics in peridynamics. However, the high computational cost is one of the main reasons limiting its usage. To improve computational efficiency of NSPD, a stability-enhanced per...

The critical local buckling instability of simply supported sinusoidal panels subjected to in-plane shear loading is investigated semi-analytically using the Rayleigh-Ritz method. Due to significant weight-strength saving and increased out-of-plane rigidity, these thin corrugated structural elements have gained wide recognition as an alternative to...

The governing differential equations of thin-walled laminated composite curved beams are derived from the principle of virtual displacement. Curvature effect is fully considered, and various displacement components of curved beams are coupled. Buckling behaviors of both the laminated composite I-section vertically (with horizontal web) and horizont...

As a nondestructive imaging technology, X-ray CT has become an effective tool for studying the microstructural damage of concrete. However, autonomous identification and segmentation of microstructural cracks remains a challenge due to the same greyscales of voids and cracks in CT images. To address this problem, this paper develops a new method fo...

Many problems may arise due to the accidental breakage of glass layers in laminated glass (LG) under extreme loads such as hard body impacts. This paper experimentally investigates the progressive post-fracture performance of double or triple layered polyvinyl butyral (PVB) LG panels under consecutive hard body impacts. Six cracking cases were init...

Laminated composite components have been widely used in engineering fields, such as aerospace engineering, automotive industries , marine structures, and civil infrastructure. Due to the inherent properties of laminated composites, the impact of local delamination defects will result in a decrease of assembly dimensional precision and mechanical pe...

The generalization and monitoring accuracy of wave propagation method using embedded piezoelectric transducers in concrete heavily depend on actuating and sensing mechanism. In this study, the actuating and sensing mechanism of extensional mode piezoelectric transducers is investigated. The theoretical analysis results reveal that the sensing mecha...

Ultra-high performance concrete (UHPC) is characterized by its superior strength, ductility, durability, and particularly its unique post-cracking performance in tension. Dog-bone–shaped specimens are widely used for determination of the tensile behavior of UHPC, but there is no standard test method or specimen design for the characterization of te...

The nonlinear stability behavior of rotationally-restrained stiffened laminated composite doubly-curved shallow shells with imperfection subjected to in-plane shear and compression loading is evaluated using a new and unique semi-analytical method. The new equivalent model with variable stiffness for both centrically- and eccentrically-stiffened sh...

Frost resistance of cementitious materials is enhanced with introduction of a series of randomly dispersed air-entrained voids. While it is understood that the improvement of frost resistance is due to the functions of cryo-suction and water reservoir of the voids, their heterogeneous, random distribution has not been considered in the modeling fra...

Measurement of the modulus of elasticity of concrete based on wave propagation technique is a critical method to assess condition and performance of concrete materials and structures. In this study, a combined numerical and experimental study is conducted for assessment of wave modulus of elasticity (WMoE) of the fully-cured concrete using surface-...

A new peridynamic virtual crack extension (PVCE) method is developed to predict the energy release rate G in fracture mechanics, and the directionally and virtually broken bonds are uniquely applied to constitute the virtual crack for crack extension in the numerical implementation. An algorithm of the PVCE method considering serial crack extension...

Nondestructive ultrasound-based methods have been applied to evaluate the elastic properties of concrete materials. Although the wave modulus of elasticity of concrete frequently is reported to be higher than the static counterpart, the microstructural and physical mechanisms are not well understood. This study conducted a computational micromechan...

Measurement of the modulus of elasticity of concrete based on wave propagation technique is a critical method to assess condition and performance of concrete materials and structures. In this study, a combined numerical and experimental study is conducted for assessment of wave modulus of elasticity (WMoE) of the fully-cured concrete using surface-...

A novel semi-analytical method is presented for buckling analysis of stiffened laminated composite plates with rotationally-restrained edges and under compression and in-plane shear loading. The equivalent model with variable stiffness for stiffened plates is developed, and the Heaviside function is uniquely used to establish the variable stiffness...

An analytical model is proposed to predict the tensile behavior of Ultra-High Performance fiber-reinforced Concrete (UHPC) with extended cyclic freezing-thawing (F-T) actions. Based on the work mechanisms of stress transfer at the matrix-fiber interface, the fiber pullout behavior is modeled, from which the combined effects of fiber orientation, fi...

A fracture mechanics-based approach is developed to predict the shrinkage cracking age of shotcrete ring specimens under various curing regimes. Prolonged water curing and curing compound are considered to mitigate early-age shrinkage cracking. The maximum allowable tensile strain is determined based on a fracture criterion using R-and G-curves. Th...

The semi-analytical solution for nonlinear stability analysis of imperfect doubly-curved laminated composite shallow shells with rotationally-restrained edges and under in-plane loading is presented. The nonlinear governing equations are established using the Galerkin method, and the arc-length and quadratic control method is implemented to capture...

In this study, the long-term performance of air-entrained shotcrete under cyclic freezing and thawing (F-T)is investigated and predicted. The dynamic modulus of elasticity and cohesive fracture energy of shotcrete at different F-T cycles are determined following ASTM C215 and RILEM TC 50-FMC, respectively. Both the test methods are found to be capa...

A computational homogenization model using microstructures obtained from X-ray micro-CT is developed to estimate the porosity-based elastic properties of ultra-high performance concrete under freeze–thaw action. The model is transformed directly from micro-CT which is capable of reflecting realistic distribution of porosity and heterogeneities insi...

A new numerical technique for whole failure progress analysis of notched plates is presented with the coupled peridynamic criterion (CPC) model, in which both the stress and energy conditions are concurrently considered. In this model, the CPC parameter of finite crack length is obtained numerically in peridynamics, and it is then applied in the wh...

In this study, a systematic pull-out simulation scheme in the formwork of two dimensional (2D) axisymmetric domain using peridynamics (PD) is presented. An axisymmetric ordinary state-based peridynamic model is used to model the pull-out deformation just like the axisymmetric stress element in the finite element method (FEM). A failure criterion ba...

The critical local buckling of simply-supported sinusoidal panels subjected to uniaxial compression using the Rayleigh-Ritz method is investigated. With increased applications of thin-walled composite structures in engineering, these corrugated panels are especially popular due to their high stiffness to weight ratio and high out-of-plane rigiditie...

Peridynamics is a nonlocal theory, and it has been applied to a series of fracture problems based on its two main bond failure criteria: the critical stretch criterion and the critical energy density criterion. In this paper, a new criterion, the critical skew criterion, corresponding to the shear deformation, is for the first time proposed specifi...

By assuming the plane-stress state in each layer, a two-dimensional elasticity model is proposed for laminated graphene-reinforced composite (GRC) beams. It is assumed that the graphene disperses uniformly in each layer but the graphene volume fraction may vary from layer to layer. For an arbitrary individual layer, the governing partial differenti...

A coupled peridynamic model combining both strength and fracture energy conditions is proposed for open-hole failure analysis of plates under tensile load. In this model, both the tensile strength (σc) and critical energy release rate (Gc) are considered to predict failure behavior of holed plates in tension, from which a coupled peridynamic criter...

A new state-based peridynamic model is proposed for quantitative elastic and fracture analysis of the orthotropic materials. In this model, four independent material parameters of two-dimensional (2D) orthotropic materials in the conventional composite mechanics model are transformed into the same number of peridynamic constants that lead to no con...

A combined analytical and experimental study using a single leg bending specimen under four-point bend loading is conducted to characterize mixed mode fracture of glass fiber reinforced polymer (GFRP)-concrete bonded interface. Both the conventional composite (rigid joint) and interface deformable (flexible joint) bi-layer beam theories are used to...

The bond behavior of epoxy-coated rebar embedded in two different ultra-high performance concrete (UHPC) mixtures is experimentally investigated by a uniaxial pullout test, and the effect of embedment length, side cover, and mixture type on the bond stress-slip relationship is predicted using a double-phase analytical model. The bond mechanism and...

Concrete structures in cold regions are exposed to cyclic freezing and thawing environment, leading to degraded mechanical and fracture properties of concrete due to microstructural damage. While the X-ray micro-/nano-computed tomography technology has been implemented to directly observe concrete microstructure and characterize local damage in rec...

In this study, a new axisymmetric ordinary state-based peridynamic (PD) model for axisymmetric problems of linear elastic solids is presented. A fracture criterion based on the PD bond energy density is proposed. Adaptive dynamic relaxation (ADR) method is adopted to obtain equilibrium solutions, and a viable fictitious density of the model is deri...

A new state-based peridynamic model is proposed to quantitatively analyze fracture behavior (crack initiation and propagation) of materials. In this model, the general relationship of the critical stretch and the critical energy release rate is for the first time obtained for the state-based peridynamic model of linear elastic brittle materials, an...

A layer-wise sandwich model is employed for vibration analysis of symmetric sandwich plates with two thin carbon nanotube-reinforced composite (CNTRC) face-sheets, in which a new polynomial refined plate theory is proposed for the core and the classical plate theory is adopted for the face-sheets. By virtue of symmetry, the in-plane displacements a...

Woven nanostructures have been acknowledged as a platform for solar cells, supercapacitors, and sensors, making them especially of interest in the fields of materials sciences, nanotechnology, and renewable energy. By employing molecular dynamics simulations, the mechanical properties of two-dimensional woven nanofabrics under biaxial tension are e...

Vibration-based nondestructive testing is an area of growing interest and worthy of exploring new and innovative approaches. The displacement mode shape is often chosen to identify damage due to its local detailed characteristic and less sensitivity to surrounding noise. Requirement for baseline mode shape in most vibration-based damage identificat...

A combined experimental, analytical and numerical study of glass fibre-reinforced polymer (GFRP)-encased concrete panels is conducted to evaluate their flexural behaviour in both longitudinal and transverse directions; the results for conventional reinforced concrete (RC) panels with the same dimensions are also presented for the sake of comparison...

In-situ, real-time structural health monitoring (SHM) of civil infrastructure via piezoelectric materials (PZT) is an emerging, sustainable method to ensure structural safety and integrity. In this study, a smart surface-mounted PZT patch system and an embedded PZT cement module system were developed to determine the wave modulus of elasticity (WMo...

Research on Lamb wave-based damage identification in plate-like structures depends on precise knowledge of dispersive wave velocity. However, boundary reflections with the same frequency of interest and greater amplitude contaminate direct waves and thus compromise measurement of Lamb wave dispersion in different materials. In this study, non-refle...

A general analytical model is developed to evaluate buckling behavior of a bilayer beam-column with a through-the-width asymmetric delamination under simply supported boundary conditions. Both transverse shear deformation and local deformation at delamination tip are taken into account in the model by considering two sublayers in both delaminated a...