Multiple Damage Events Research Articles

Structural Damage Identification Based on Convolutional Neural Networks and Improved Hunter–Prey Optimization Algorithm

Accurate damage identification is of great significance to maintain timely and prevent structural failure. To accurately and quickly identify the structural damage, a novel two-stage approach based on convolutional neural networks (CNN) and an improved hunter–prey optimization algorithm (IHPO) is proposed. In the first stage, the cross-correlation-based damage localization index (CCBLI) is formulated using acceleration and is input into the CNN to locate structural damage. In the second stage, the IHPO algorithm is applied to optimize the objective function, and then the damage severity is quantified. A numerical model of the American Society of Civil Engineers (ASCE) benchmark frame structure and a test structure of a three-storey frame are adopted to verify the effectiveness of the proposed method. The results demonstrate that the proposed approach is effective in locating and quantifying structural damage precisely regardless of noise perturbations. In addition, the reliability of the proposed approach is evaluated using a comparison between it and approaches based on CNN or the IHPO algorithm alone. The comparison results indicate that in single and multiple damage events, the proposed two-stage damage identification approach outperforms the other two approaches on the accuracy, and the average consumption time is 20% less than the method using the IHPO algorithm alone. Therefore, this paper provides a guideline for the study of high-accuracy and quick damage identification using both data-based and model-based hybrid methods.

Implementation of the regularized extended finite element method in Abaqus framework for fracture modeling in laminated composites

The Regularized eXtended Finite Element Method (Rx-FEM) is a fracture mechanics based technique for progressive failure simulation when multiple damage events such as matrix cracks and delamination are introduced into the finite element model via mesh independent displacement discontinuities. In the Rx-FEM, the Heaviside step function that is used in the eXtended Finite Element Method (x-FEM) is replaced by a continuous function approximated by using the FE shape functions. This regularization offers unique possibility for the implementation of the Rx-FEM methodology in commercial FE software as a superposition of native elements as opposed to a single user defined element which is the approach taken by x-FEM implementation to date. The advantages of the novel Rx-FEM implementation lie in the ability to utilize the capabilities of the host software including contact, geometric nonlinearity as well as post-processing, and visualization. The proposed implementation of the Rx-FEM methodology is illustrated for commercial software Abaqus on a number of examples of mesh-independent crack modeling in composite laminates, and delamination between plies. The validity of the proposed implementation is demonstrated by comparing with experimental data and benchmark solutions.

Enhanced Mixing of Microvascular Self-Healing Reagents Using Segmented Gas-Liquid Flow.

Microvascular self-healing systems have previously been demonstrated to restore large-scale damage and achieve repeated healing of multiple damage events in polymers. However, the healing performance of these systems is often limited because thelaminar nature of flow in microchannels results in poor mixing of two-part self-healing reagents. In this paper, we introduce segmented gas-liquid flow (SGLF) to enhance the mixing of reagents in microvascular self-healing systems. In SGLF, discrete liquid slugs containing self-healing reagents are separated by gas bubbles while flowing through a single microchannel. Recirculating streamlines within the liquid slugs can enhance the mixing of miscible liquids such as healing reagents. We investigate the effect of SGLF on mixing and healing for a two-stage chemistry used to restore large-scale damage in thermoset polymers. Additionally, we employ SGLF to deliver an epoxy-thiol chemistry, enabling the repeated recovery of fracture toughness in glass fiber-reinforced composites. In both systems, the mixing of healing agents delivered by SGLF is enhanced compared to alternative microvascular delivery strategies. For the two-stage chemistry, SGLF increases the maximum damage size that can be healed by 25% compared to laminar single-phase flow. Furthermore, there are concomitant increases in the extent of polymerization and the mechanical properties of the restored material, including a fivefold increase in the peak load sustained during a push-out test. For the epoxy-thiol chemistry, SGLF enables multiple healing cycles with healing efficiency above 100%. On the basis of these results, we envision that SGLF could improve performance for a variety of microvascular self-healing systems with different host materials, damage modes, and healing chemistries.

A Microvascular System for the Autonomous Regeneration of Large Scale Damage in Polymeric Coatings

Self‐healing polymers are capable of self‐repair either in response to the damage or through external stimuli, but are limited in their ability to autonomously control the volume of healing agents released, in the length scale of damage they address, and in their ability to respond to multiple damage events. Here, the authors report a novel design for healing agent storage and release for vascular coating systems that allows for complete regeneration of a coating with precise and autonomous control of coating thickness. A variety of healing agent formulations that cure under ambient sunlight are explored and their cure profiles and mechanical properties are reported. In the proposed vascular coating system, the stored healing agent remains stable within the network until large‐scale damage (e.g., abrasion) completely removes the protective coating. A precise volume within the network is then released, and cures when exposed to simulated sunlight to reform the protective coating. This coating system facilitates consistent coating thickness and hardness for several cycles of coating removal and regeneration.

Micromechanical modelling of the progressive failure in unidirectional composites reinforced with bamboo fibres

A multiscale approach based upon the micromechanical analysis of multiple damage events at the fibre/matrix scale is developed to investigate the mechanical behaviour of unidirectional composites subjected to tensile loading. The composites are reinforced with bamboo fibres under conditions of fibre breakage and matrix transverse cracking, by considering longitudinal splitting derived from the weak interfacial bonding between fibre and matrix. Due to the statistical nature, an improved Weibull model is employed to describe fibre strength distributions affected by the diameter change in the fibres. A simulation scheme coupled with the Monte Carlo method is performed to characterise the progressive failure in the composite. Compared with experimental results, the validity of the model for composite strength prediction is examined as well.

Self-Healing of Microcracks in Engineered Cementitious Composites (ECC) Under a Natural Environment.

This paper builds on previous self-healing engineered cementitious composites (ECC) research by allowing ECC to heal outdoors, in the natural environment, under random and sometimes extreme environmental conditions. Development of an ECC material that can heal itself in the natural environment could lower infrastructure maintenance costs and allow for more sustainable development in the future by increasing service life and decreasing the amount of resources and energy needed for repairs. Determining to what extent current ECC materials self-heal in the natural environment is the first step in the development of an ECC that can completely heal itself when exposed to everyday environmental conditions. This study monitored outdoor ECC specimens for one year using resonant frequency (RF) and mechanical reloading to determine the rate and extent of self-healing in the natural environment. It was found that the level of RF, stiffness, and first cracking strength recovery increased as the duration of natural environment exposure increased. For specimens that underwent multiple damage cycles, it was found that the level of recovery was highly dependent on the average temperature and amount of precipitation between each damage event. However, RF, stiffness, and first cracking strength recovery data for specimens that underwent multiple loading cycles suggest that self-healing functionality can be maintained under multiple damage events.

Stress profiles around broken fibers in unidirectional composites using influence superimposition technique

The stress transfer from broken to its unbroken adjacent neighboring fibers in unidirectional fibrous composites under a tensile loading applied in the fiber axis is analyzed using a two-dimensional (2D) shear lag model. The numerical solutions to the governing equations is greatly simplified by the assumptions that the displacements perpendicular to the fiber direction can be ignored, and the axial displacements are uniform over the cross section of any fiber. Using an influence function superimposition technique, closed-form analytical expressions are used to predict stress profiles in both the fiber and matrix because of any number and arbitrary array of fiber breaks in the presence of matrix shear failure. These are compared to stress concentrations predicted using the finite element analysis (FEA). It is shown that the 2D modeling presented here does generalize the governing equations to include interactions with multiple damage events. The micromechanical model is vital to develop the basic mechanics that are necessary to understand failure behavior of the composite produced by the failure of one or more of its components. POLYM. COMPOS., 2013 © 2013 Society of Plastics Engineers

Blind identification of damage in time-varying systems using independent component analysis with wavelet transform

This paper proposes a novel output-only damage identification method based on the unsupervised blind source separation (BSS) technique termed independent component analysis (ICA). It is discovered that ICA biases to extract sparse component, which typically indicates damage, from the observed mixture signals. The measured structural responses are first preprocessed by wavelet transform (WT). The wavelet-domain signals are then fed as mixtures into the BSS model, which is solved by ICA. The obtained “interesting” source with sharp spike and its associated spatial signature in the recovered mixing matrix reveal damage instant and location respectively. Following which, identification of the time-varying modes is carried out by ICA using the structural responses before and after the identified damage instant. For illustration, numerical simulations are conducted, where damage is modeled by abrupt stiffness variation in the time-varying system. Experimental and real-world seismic-excited structure examples with time-varying stiffness are also presented to illustrate the capability of the developed WT–ICA method. Results show that the WT–ICA algorithm realizes accurate and robust blind identification of damage instant and location in single or multiple damage events.

Plant Induced Defenses Depend More on Plant Age than Previous History of Damage: Implications for Plant-Herbivore Interactions

Herbivore-induced plant responses can significantly change as a function of plant developmental stage and previous history of damage. Yet, empirical tests that assess the combined role of multiple damage events and age-dependent constraints on the ability of plants to induce defenses within and among tissues are scarce. This question is of particular interest for annual and/or short-lived perennial plant species, whose responses to single or multiple damage events over a growing season are likely to interact with ontogenetic constraints in affecting a plant's ability to respond to herbivory. Using Plantago lanceolata and one of its specialist herbivores, Junonia coenia, we examined the effect of plant ontogeny (juvenile vs. mature developmental stages) and history of damage (single and multiple damage events early and/or late in the season) on plant responses to leaf damage. Plant responses to herbivory were assessed as induced chemical defenses (iridoid glycosides) and compensatory regrowth, in both above- and below-ground tissues. We found that constitutive concentration of iridoid glycosides markedly increased as plants matured, but plant ability to induce chemical defenses was limited to juvenile, but not mature, plant stages. In addition, induced defenses observed 7d following herbivory in juvenile plants disappeared 5wk after the first herbivory event, and mature plants that varied considerably in the frequency and intensity of damage received over 5wk, did not differ significantly in their levels of chemical defenses. Also, only small changes in compensatory regrowth were detected. Finally, we did not observe changes in below-ground tissues' defenses or biomass a week following 50% removal of leaf tissues at either age class or history of damage. Together, these results suggest that in P. lanceolata and perhaps other systems, ontogenetic trajectories in plant growth and defenses leading to strong age-dependent induced responses may prevail over herbivore-induced indirect interactions.

Numerical Modeling of Tensile Behavior of Fiber-reinforced Polymer Composites

Based upon micromechanical analysis of multiple damage events, a 2D theoretical model has been proposed to study tensile mechanical response of fiber-reinforced polymer composites, by considering the effect of statistic variations in fiber strength and shear failure of matrix. Stress profiles for any configuration of breaks in composites are derived by a superposition method under the framework of shear-lag arguments. A simulation scheme coupled with Monte-Carlo method has been executed to simulate progressive damage and to investigate failure behavior. Results show that the ultimate strength of composites is influenced by fiber strength statistics and stress distribution due to progressive microdamage.

Micromechanical Modeling of the Effect of Progressive Damage on the Tensile Behavior in Fiber-Reinforced Polymer Composites

In this article a methodology based upon micromechanical analysis of multiple damage events is developed to predict stress-strain response and failure behavior of fiber-reinforced polymers composites under tensile loading, by considering the effect of variations in fiber strength and local shear failure of the matrix. A simulation scheme coupled with Monte-Carlo method including these failure mechanisms is proposed to investigate failure process and determine ultimate strength of the composites. It is shown that the size dependence of composite ultimate strength is dominated by fiber strength statistics and stress distribution due to progressive microdamage.

Evolution of Damage in Near α IMI-834 Titanium Alloy Under Monotonic Loading Condition: A Continuum Damage Mechanics Approach

In the present work, a continuum damage mechanics model, based on Lemaitre’s concept of equivalent stress hypothesis (1986, “Local Approach to Fracture,” Eng. Fract. Mech., 25, pp. 523–537), has been applied to study the evolution of damage under monotonic loading condition in a near α IMI-834 titanium alloy, used for aeroengine components in compressor module. The damage model parameters have been experimentally identified by in situ measurement of damage during monotonic deformation using alternating current potential drop technique. The damage model has been applied to predict damage evolution in an axisymmetrically notched specimen using finite element analysis. A reasonably good agreement has been observed between numerically simulated and experimentally measured damage behaviors. Damage micromechanisms operative in this alloy have also been identified which show multiple damage events.

Damage identification of flexible beam structures using large displacements

In previous works we have proposed a damage location strategy for flexible beam structures where non-linear displacements are observed. The present paper deals with the computation of physical characteristics associated with detected damages. Even using a preliminary location stage allowing to reduce the set of parameters, the problem of their evaluation is made difficult because of the non-linearities. There is a strongly non-linear ill-posed problem to solve. For correlating measured data with the given modelling, a measure of the error on the constitutive relation is written. The computation of the damages is made in a very general development within the framework of the continuum media mechanics and can be applied using different numerical approaches. The introduction of supplementary experimental information such as the measured strain helps the strategy. To illustrate the method, we choose a finite element discretization. The ability to quantify single and multiple damage events is investigated through a set of numerical examples.

Damage detection in beam structures using subspace rotation algorithm with strain data

Motivated by a smart structures philosophy of self-health monitoring in structural systems, a damage detection system for beam structures using subspace rotation techniques is presented. In doing so, the subspace rotation is extended from displacement-based data to strain-based data. Methods for accommodating the additional degrees of freedom of beam elements are presented. Using simulated data, the ability to locate and quantify single and multiple damage events is investigated. It has been found that the higher-order vibration modes are required to locate damage events in beams because the frequency response of beams is much less sensitive to a damage event than that of truss structures. It has also been found that condensation methods cannot be used to remove rotational degrees of freedom in the beam because of the coupled nature of the rotational degrees of freedom to the translational degrees of freedom.