Mijia Yang

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.

Fatigue Life Prediction of Pultruded E-glass/Polyurethane Composites

In this article, the tension–tension fatigue behavior of newly developed pultruded E-glass/polyurethane composites is characterized, and an improved model for fatigue life prediction including the effects of stress ratio, frequency, and mean stress as the testing parameters is proposed. The proposed non-dimensional analysis is in good agreement with the predictions of existing available fatigue data and present testing data. The model is consistent with the Goodman line relationship and has a clear physical meaning. The fatigue test data of E-glass/polyurethane composites are analyzed using the proposed model, and they are compared with other common E-glass fiber-reinforced plastic composites. It indicates that the E-glass/polyurethane composites are more fatigue sensitive but comparable to other fiber-reinforced plastic composites in their fatigue behaviors. The effects of stress ratio, frequency, and mean stress on fatigue life of E-glass/polyurethane composites are studied and discussed. The corresponding S–N curve and its bounds based on 95% confidence are provided for the pultruded E-glass/polyurethane composites. The present fatigue model can be used as a useful tool to characterize the effects of various parameters on the fatigue behavior of fiber-reinforced plastic composites, and it provides the fatigue life prediction for newly developed pultruded E-glass/polyurethane composites.

Impact location and load identification through inverse analysis with bounded uncertain measurements

The growing demand for real-time damage assessment necessitates development of an efficient inverse analysis algorithm with consideration of practical issues such as uncertainty in measurement. A mathematical model-based inverse analysis scheme is proposed to identify impact locations and reconstruct impact load time history of a simply supported plate through multiple levels of analysis. The proximity of the impact location is first determined by the triangulation method and the impact location is then refined by minimization of an objective function through the particle swarm optimization method (PSO). Loss of data due to filtration is addressed in a further level by performing an interval analysis based on extreme measurement errors. The outcome of the analyses is a mean impact location, a load time history, and a range of likely deviations. The extreme deviation in impact location is shown by bounding lines, which form a rectangle. The deviation in load time history is also shown by upper and lower bounding sinusoidal curves. The results of the analyses indicate that the proposed method can effectively locate the impact point and reconstruct the load time history even with the existence of noise in the measured response.

Impact and Damage Prediction of Sandwich Beams with Flexible Core Considering Arbitrary Boundary Effects

In this study, a higher-order impact sandwich beam model is presented to simulate the response of a soft-core sandwich beam subjected to a foreign object impact. The effects of asymmetric lay-up of the sandwich and arbitrary boundary conditions are accounted for in the analysis, and the solution is obtained by employing a finite difference method (FDM). A static and free vibration problem of sandwich beams is first solved, and the results are validated by comparing with the numerical finite element predictions of ABAQUS. The validity of the impact response is then examined using the LS-DYNA model. The contact force and deflection history as well as the propagation of axial, shear, and transverse normal stresses in the sandwich beams during the impact are analyzed. The local effect at the boundary and the loading location is captured by the present model, and the influences of boundary conditions (i.e., the top face sheet free and the bottom pin—pin supported versus both the top and bottom face sheets clamped) and the load spreading process on the impact behavior are discussed. The calculated stresses under the foreign object impact are further incorporated with the failure criteria to assess the failure location, time, and mode in the sandwich beams. The damage induced by the impact process is predicted and comprehensively compared with the experimental results. The higher-order impact model of sandwich beams with the FDM provides accurate predictions of the generated stresses and induced damage, and it can be used effectively in design analysis of anti-impact structures made of sandwiches.

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.

Modeling and Failure Analysis of Elastic-Plastic Sandwich Beams

Based on a strict and novel decomposition of deformation patterns of a sandwich beam under transverse loading, the flexural and indentation responses of sandwich beams are analyzed with consideration of elastic-plastic behavior of the crushable core material. The analytical model is capable of predicting the flexural response, indentation failure load, and indentation deformation. Some interesting phenomena, such as the global elastic-plastic hardening behavior and three distinct failure stages, are revealed using the present approach. Different from the existing plastic foundation model, a generic model for analyzing the flexural and indentation responses of the elastic-plastic sandwich beams is proposed, and it sheds new light on the effects of skin membrane and elastic-plastic core during indentation process.

Creep Design of Epoxy Bonded Anchor System

This article presents a systematic study on creep design of epoxy bonded anchor system. First, a theoretical model for prediction of long-term performance of an anchor system is suggested assuming epoxy layer following Maxwell visco-elastic behavior, which is then validated through an ABAQUS numerical model. A close match between the ABAQUS result and the theoretical model has been reached. Next, a general-purpose methodology for estimating creep capacity of an adhesive bonded anchor system is suggested following AC58 and two creep capacity equations are reached for Model Dry Epoxy and Model Wet Epoxy bonded anchor systems. The derived creep capacity is then used to re-examine the Boston D Tunnel anchor design and a safe design is reached through the suggested method considering the anchor systems long-term creep performance. Last, the ABAQUS model is extended to include the effect of curing temperatures, which shows significant influences of curing temperature on the capacity of an epoxy bonded anchor system.

Warrants for Active Warning Devices at Low-Volume Highway-Rail Grade Crossings

In order to utilize funds from the Highway-Rail Grade Crossing Safety Program, Section 130 of Title 23 United States Code (U.S.C.), states must prioritize public highway-rail crossings for improvements. With nearly 10,000 open public crossings in Texas to prioritize for Section 130 funds, an automated ranking procedure capable of generating a useful priority list can be instrumental for efficient fund allocation. Findings from this research were used develop the following products: warrants to identify crossings that may benefit from upgrades; revised Texas Priority Index (TPIrev); the Texas Passive Crossings Index (TPCI); and an integrated prioritization methodology.

Impact Response of Elastic and Elastic-plastic Sandwich Beams

An original model for impact analysis of elastic-plastic sandwich beams is presented, and the effect of sandwich damping is uniquely introduced in the analysis by considering the gradient of beam compliance. By incorporating the compliance (or stiffness) and compliance gradient of the sandwich beams to the equation of motion of the projectile, the standard mass-spring model for the sandwich system is uniquely recovered. Both the elastic and elastic-plastic impact processes are analyzed and compared with elastic model of no sandwich damping effect (i.e., the linearized model by Qiao et al. (2004)). The proposed impact model is validated with the elastic finite element analysis using LS-DYNA. A parametric study on the influences of velocity and mass of the projectile on the impact response of elastic and elasticplastic sandwich beams is conducted, and it reveals the significant contribution of the sandwich damping and plasticity to the impact response. Keyword: Elastic-plastic sandwich beam, bending, plasticity, impact, damping effect, compliance, sandwich

Guided-wave based damage detection method for various materials using piezoelectric sensors/actuators

In this study, the guided wave technique is applied to nondestructively assess the damage in various engineering materials, like alumina, laminated composites, and composite sandwiches. A combined theoretical, numerical and experimental investigation 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 inside damages 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. In particular, the experimental results on damage detection of the composite sandwich beams are reported and discussed. 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.