Publications

A coupled honeycomb composite sandwich bridge-vehicle interaction model

This paper presents a coupled, dynamic vehicle and honeycomb composite sandwich bridge deck interaction model.The composite sandwich deck consists of E-glass fibers and polyester resin.Its core consists of corrugated cells in a sinusoidal configuration along the travel direction.First, analytical predictions of the effective flexural and transverse shear stiffness properties of the sandwich deck were obtained in the longitudinal and transverse directions.These were based on the modeling of equivalent properties for the face laminates and core elements.Using the first order shear sandwich theory, the dynamic response of the sandwich deck was analyzed under moving dynamic loads.A dynamic vehicle simulation model was used for the latter, assuming that the deck response is the only source of excitation (i.e., its roughness was assumed to be negligible).Subsequently, the dynamic load factors of the sandwich bridge deck were calculated for different traveling velocities.The results suggest that the dynamic load factors vary with the traveling speed and increase significantly with decreasing deck stiffness.Considering multiple degrees of freedom for the vehicle further amplifies the dynamic loading factor and increases the vibration generated by vehicles.

Topology Optimization and 3D Printing of Three-Branch Joints in Treelike Structures

Optimization and intelligent manufacturing are of particular interest and important to improve the severe situation of excessive mass and uneven stress distribution for three-branch joints in treelike structures. In this work, the optimal shape of the three-branch joints under vertical load is studied by topology optimization method, and the complex topology optimization joint is manufactured using three-dimensional (3D) printing technology because it is difficult to produce by conventional manufacturing processes. First, the original model is optimized by using the OptiStruct solver in HyperWorks version 14.0 (64-bit) software, and the element density cloud map and element isosurface map of the model are obtained. Then, the static behaviors of the topology optimization model are compared with those of the hollow spherical joint model which is commonly used in engineering and those of the bionic joint model based on empirical design. Finally, the 3D printing technology is used to produce the topology optimization joint model, the hollow spherical joint model, and the bionic joint model. The process of production is characterized by converting the finite-element file of topology optimization joint into a standard template library (STL) file and then reading it into the slicing software to generate the 3D printing commands. The results show that the topological optimization joint has the most balanced stress distribution and the best static behaviors, which can provide reference for the design of joints in treelike structures. It is effective and feasible to use the combined technology of topology optimization and 3D printing to design and manufacture three-branch joints.

Experimental Verification of Lamb Wave Identification of Delamination Defects through Covariance of Energy Change

Delamination is currently a difficultly-detectable form of damage in composite laminate materials. This paper experimentally validates an innovative method that more easily detects delamination damage within composite materials through the covariance of energy change. Lamb waves were introduced and recorded through an actuator and sensors made of piezoelectric material. The data was then analyzed through the Fast Fourier Transform (FFT). Using the data from FFT, the idea of covariance of energy change was suggested to correlate with defect characteristics. By comparing the covariance of energy change in beams with different delamination sizes and depths, correlations between the covariance of energy loss and defect characteristics were developed. With these correlations, the severity of these damages was quantified.

Effect of Carbon Dioxide Curing on Cement Pastes Through Drt Analysis of Eis Data

: Early-age carbon dioxide curing (EACC) is one of the promising methods for carbon dioxide (CO2) sequestration and utilization in cement-based materials which, in addition to CO2 mineralization, has the potential to improve the engineering properties of construction materials. Understanding the effect of EACC on the electrochemical properties of hydrated cement provides an insight for its hydration evolution and mechanical performance. In this study, the effect of EACC on the electrical properties of cement pastes with various water contents using electrochemical impedance spectroscopy (EIS) was investigated. The conventional method for interpretation of EIS data is fitting Nyquist plots by equivalent circuits models (ECMs) however this method does not provide accurate analysis at early age hydration. Instead, the distribution of relaxation times (DRT) method for extracting parameters of electrical interfaces and time domain properties was proposed. Using the DRT analysis, two peaks are identified in the EIS data representing two interfaces in the electrochemical cell including the electrode-cement and pore structure interfaces, and the parameters of each interface were extracted. The results show that cement bulk resistance, the resistance of the electrode-cement interface, and the pore structure resistance of the cement paste profile increased with respect to CO2 curing.

Effect of Fiber Content and Alignment on the Mechanical Properties of 3D Printing Cementitious Composites

This paper studies aligned glass fiber-reinforced composites for printing. To determine the influence of fiber content and alignment on the mechanical properties of this novel material, a large number of standard test specimens were prepared, which included samples fabricated by mold-casting, randomly dispersed fiber reinforced mixtures and aligned fiber cement composites containing 10 types of fiber volume ratios manufactured by nozzle sizes ranging of 24 and 10 mm (fiber length = 12 mm). Mechanical properties and failure modes of the specimens under compression and flexural tests were studied experimentally. The anisotropic behaviors of printed samples were analyzed by different loading directions. As a result, the compressive and flexural strength of printed samples showed obvious anisotropy. With the increase of fiber volume ratio, flexural strength of the fiber reinforced composite was elevated tremendously but its compression strength reduced slightly. Moreover, fiber alignment also had a significant influence on the mechanical properties of the fiber reinforced composite. The composite cement-based material with 1 vol.-% aligned fiber exhibited an excellent flexural strength of 9.38 MPa, which increased by 483% in comparison to that of the plain cement paste.

Scanning and separating vertical and torsional–flexural frequencies of thin-walled girder bridges by a single-axle test vehicle

An effective procedure is proposed for scanning and separating the vertical (flexural) and torsional–flexural frequencies of thin-walled girder bridges by a moving single-axle test vehicle, modeled as a two degree-of-freedom (DOF) system to account for the vertical and rocking motions. The response of the vehicle is not directly used, since it may mask the bridge frequencies by self frequencies. Instead, the wheel-bridge contact responses are used for being free of vehicle’s frequencies. To start, closed-form solutions are derived for the vertical, lateral, and torsional vibrations of the mono-symmetric beam. Then, the contact responses are calculated from the vehicle responses, considering the discrete nature of field data. The vertical and torsional–flexural frequencies of the bridge are separated by using the vertical and rocking motions derived from the contact responses without prior knowledge of the mode shapes. The proposed technique is numerically validated with the following conclusions: (1) the wheels’ contact responses outperform the vehicle response in that more high frequencies of the bridge can be detected; (2) the torsional–flexural​ frequencies can better be detected from the wheel closer to the bridge edge; and (3) the vertical and torsional–flexural frequencies of bridges can be successfully separated by the proposed procedure even in the presence of pavement roughness, which is helpful for field applications.

Large Displacement Detection Using Improved Lucas–Kanade Optical Flow

Displacement is critical when it comes to the evaluation of civil structures. Large displacement can be dangerous. There are many methods that can be used to monitor structural displacements, but every method has its benefits and limitations. Lucas-Kanade (LK) optical flow is recognized as a superior computer vision displacement tracking method, but it only applies to small displacement monitoring. An upgraded LK optical flow method is developed in this study and used to detect large displacement motions. One motion controlled by a multiple purpose testing system (MTS) and a free-falling experiment were designed to verify the developed method. The results provided by the upgraded LK optical flow method showed 97 percent accuracy when compared with the movement of the MTS piston. In order to capture the free-falling large displacement, the pyramid and warp optical flow methods are included in the upgraded LK optical flow method and compared with the results of template matching. The warping algorithm with the second derivative Sobel operator provides accurate displacements with 96% average accuracy.

Investigation of shale fracture behavior with different bedding properties based on discrete element method

Effectiveness of chemical treatment on polypropylene fibers as reinforcement in pervious concrete

Fiber reinforcement delays the crack generation and enhances the strength of the host matrix. However, the bonding mechanism between fiber and concrete matrix is controversial in literature and needs better explanation. Due to surface smoothness and inert chemical nature of commercially available fibers, several mechanical and chemical treatment techniques have been studied by researchers to increase the fiber-matrix bonding properties. The use of fibers in pervious concrete is even more challenging due to high porosity and insufficient fiber-matrix bonding interface. This study discusses the effect of chemical treatment on short polypropylene fibers and its uses in pervious concrete as reinforcement. The change in fiber surface due to the treatment is determined through fiber wettability test and Atomic Force Microscopy (AFM). Changes on the tensile strength of fibers by the treatment methods are also tabulated. Single fiber pullout tests are conducted to study the effect of the treatment type on fiber-cement interface properties. Treated fibers are then put into pervious concrete matrix for compressive and flexural strength tests. Chemical treatments are found to improve the surface roughness and cement matrix interface properties, as well as to enhance the overall strength of the fiber reinforced pervious concrete.

Preparation and characterization of a novel microporous PE membrane supporting composite gel polymer electrolyte

A new type of composite gel polymer electrolyte(CGPE) with a blend of polyethylene glycol 200 maleate, methyl methacrylate(MMA) and poly(methyl methacrylate)(PMMA) coated and polymerized on the microporous polyolefin membrane was prepared by means of ultra-violet crosslinking and then soaked in a lithium salt solution. The chemical construction, morphology, ionic conductivity of composite gel polymer electrolytes, and their interfacial stability between lithium metal electrode were characterized by using infrared spectroscopy, 1H NMR measurement, scanning electron microscopy, alternating current impedance and linear sweep voltammetry, respectively. The ionic conductivity of the CGPE reaches 10−3 S/cm at room temperature and its electrochemical stability window is 4.7 V, which makes it a potential candidate for application as polymer electrolyte in devices.

Static and Nonlinear Impact Analyses of Free–Free Sandwich Plates on a Solid Half-space

In this study, an elastic model for static and nonlinear impact responses of a composite sandwich plate on an elastic half-space including the anti-plane core effect is developed. The effects of the elastic half-space and the anti-plane core are studied, and the contact force history and maximal deflection are predicted. Compared to the available analytical static analysis of rigid plates on a solid half-space and the numerical finite element modeling using LS-DYNA, the proposed theoretical method shows its validity and advantages in predicting the static and impact behaviors of sandwich plates sitting on a solid half-space. The predicted non-uniform distribution of transferred force under static load sheds new light on the understanding of force action mechanism between the sandwich system and the solid half-space. The two important impact factors (i.e., the maximal deflection and the peak contact force) provided by this study can be used to determine the damage size and position. Further, the semi-analytical model developed can be served as a basis for optimal design of fully backed sandwich collision protection systems, of which both minimizing the rebounded residual velocity of the projectile and keeping the underneath protected structures intact are important.

Adsorption mechanism of carbonate ion on the (111) surface of tricalcium silicate through DFT simulations

No abstract is provided for this article.

Impact event identification through real-time strain measurements

Impact event identification is a primary concern in many structural health monitoring applications. Model-based inverse analysis is a common approach for system identification as long as the physical model can accurately capture the behavior of structure. A layered analysis including estimation of impact location (IL) in the first layer and reconstruction of impact load time history (ILTH) in the second layer was proposed. An implementation of the theory on a simply supported plate structure is conducted in this study. The results indicate that the proposed inverse scheme is capable of detecting impact location and reconstructing impact load time history with a satisfactory precision. Due to presence of system error, a suitable cost function has to be chosen to guide the fitting process toward the desired parameters.

Effect of Prestress on Bridge–Vehicle Interactions

Prestress applied on bridges affects the dynamic interaction between bridges and vehicles traveling over them. In this paper, the prestressed bridge is modeled as a beam subjected to eccentric prestress force at the two ends, and a half-vehicle model with 4 degrees of freedom is used to represent the vehicle passing the bridge. A new bridge–vehicle interaction model considering the effect of prestress with eccentricity is developed through the principle of virtual work. The correctness and accuracy of the model are validated with literature results. Based on the developed model, numerical simulations have been conducted using the Newmark’s β method to study the effects of vehicle speed, eccentricity and amplitude of the prestress, and presence of multiple vehicles. It is shown that prestress has an important effect on the maximum vertical acceleration of vehicles, which may provide a good index for detecting the change of prestress. It is also interesting to find that the later-entering vehicle on the prestressed bridge will largely reduce the maximum vertical acceleration of the vehicle ahead of it.

Physical and Mechanical Properties of Cornstarch-Based Construction Materials in Place of Cement

Concrete is used globally due to its useful mechanical and durability properties. However, concrete requires a massive amount of cement, which is the second-largest source of carbon emission (5-7% of global CO2 emission) due to its high energy consumption. The gelatinization effect of corn starch as a binder has been explored in the place of cement in concrete. However, there is a need to optimize the various processing conditions to enhance the material's strength of this corn starch-based material known as CoRncrete. Two experiments were conducted to optimize the ratio of sand, starch, water, curing temperatures, and time. The compressive and tensile strength of the CoRncrete samples were analyzed. The results showed that the optimum processing conditions having the sand grain size of 0.250-0.425 mm, the mixture ratio of starch, water and sand 1:1:5, curing temperature and time of 110 °C and 24 h can yield a maximum compressive strength up to 18.9 MPa. Statistical analysis revealed that the size of sand grains and curing temperatures had the most significant impact on the material's strength. Microstructural analysis, employing scanning electron microscopy (SEM) and micro computed tomography (microCT), unveiled numerous internal pores and cracks within the hardened cubic blocks, which significantly decreased the strength. Consequently, future investigations should concentrate on reducing internal pore spaces and cracks to enhance the durability of CoRncrete.

Modeling and experimental detection of damage in various materials using the pulse-echo method and piezoelectric sensors/actuators

The application of guided wave techniques to nondestructively determine the structural integrity of various engineering materials, like alumina, laminated composites, and composite sandwiches, is presented. In particular, a combined theoretical, numerical, and experimental investigation of the fundamental aspects of the pulse-echo method using piezoelectric sensors and actuators is conducted. The dispersion effect of wave guides on these materials is first analyzed, and the transient propagation process of wave guides and its interaction with internal damage are then numerically simulated. The implementations of the pulse-echo method are illustrated in experimental testing and damage detection of aluminum beams, carbon/epoxy laminated composite plates, and composite sandwich beams. The effects of frequencies, wave forms, and types of piezoelectric material on the damage detection process are discussed, in consideration of locating damage in structures. As illustrated in this study, the pulse-echo method combined with piezoelectric material can be used effectively to locate damage in various engineering materials and structures.

Dynamic responses of prestressed bridge and vehicle through bridge–vehicle interaction analysis

Existence of prestress in bridges affects the dynamic responses of both bridges and vehicles traveling over them. In this paper, the bridge is modeled as a continuous beam with eccentric prestress, and a half-vehicle model with 4 degrees of freedom is used to represent the vehicle passing the bridge. A new bridge–vehicle model with consideration of prestress effect is created through the principle of virtual works to investigate the continuous prestressed bridges and vehicle interaction responses. The correctness and accuracy of the model are validated with literature results and Abaqus model. Based on the created model, numerical simulations have been conducted using the Newmark integration method to perform a parametric study on effects of number of bridge span, span length, eccentricity and amplitude of prestress. It is shown that prestress has a significant effect on the maximum vertical acceleration of vehicles, which may provide a good index for detecting the change of prestress.

Robust form finding of tree-like structure by improved slime mould algorithm

To achieve a robust and efficient form finding design for tree-like structures, this study proposes an innovative form finding approach based on an improved slime mould algorithm. This method leverages the loads and coordinates of each support joint within the tree-like structure as initial conditions and defines the solution space according to the structural configuration, aiming to minimize the bending moments at the joints. To circumvent freezing problems during iterations, the improved slime mould algorithm is deployed to iteratively determine joint positions at each hierarchical level, starting from top and moving downward, thereby accomplishing the overall form finding for the tree-like structure. After the form is established, the cross-sectional dimensions of the structure are optimized for weight reduction while ensuring that the design meets a variety of performance criteria. As a case study, the tree-like structural columns in Dalian Jinzhou Bay Airport are used to demonstrate the specific implementation procedures of form finding and section optimization. A comparative analysis is performed between the optimized design and the original structure. The research findings reveal that, in comparison to the initial structure, the optimized structure experienced a 27.7 % reduction in maximum combined stress, a 1.8 % decrease in total deformation, a 22.1 % reduction in mass, and an enhancement in stability. These results confirm the effectiveness of the improved slime mould algorithm in tree-like structure form finding and section optimization and adding a section optimization stage makes the optimization process of the tree-like structure more complete, thereby avoiding the phenomenon of excessive self-weight after form finding and making the optimization results more reasonable.