Ahmed Abuzaid

Crack propagation until fracture is an important criterion to predict a structure‘s service life. In order to increase the latter, the cracked component needs to be repaired or replaced. In the present study, a finite element analysis has been carried out to investigate the effects of adhesive thickness, patch thickness and crack length on the passive repair performance of a center-cracked rectangular aluminum plate under mode-I loading condition using an ANSYS package. A comprehensive parametric study shows that the stress intensity factor is influenced by the patch thickness, patch size, adhesive material, and adhesive thickness. ABSTRAK: Penyebaran retak sehingga patah adalah kriteria penting bagi menjangka hayat struktur. Bagi memanjangkan jangka hayat struktur, komponen keretakan perlu dibaik pulih atau diganti. Kajian ini telah menjalankan analisis elemen tak terhingga bagi mengetahui kesan ketebalan pelekat, ketebalan tampalan dan panjang retak pada bahagian keretakan tengah plat petak aluminium yang dibaiki secara pasif, menggunakan pakej ANSYS di bawah beban mod-I. Kajian parametrik yang menyeluruh menunjukkan faktor tekanan intensif dipengaruhi oleh ketebalan tampalan, saiz tampalan, bahan pelekat dan ketebalan pelekat.

This article proposes an alternative model for active repair for an edge-cracked plate with adhesively bonded piezoelectric actuator. It computes the Mode-I stress intensity factor (SIF) produced by the piezoelectric actuators using appropriate derived geometrical weight functions. Furthermore, this article presents an experimental study to verify the proposed analytical model and the finite element analysis using ANSYS software. Therefore, the analytical, finite element and experimental results for Mode-I opening of the crack conditions are demonstrated. Parametric analysis to understand the influence and to study the efficiency of the piezoelectric actuator on mitigation of the Mode-I SIF was conducted. The obtained analytical solution is applicable in the calculation of Mode-I SIF with reasonable accuracy. The result indicated that the maximum reduction of SIF is achieved with the application of high external voltage and thin thickness actuator. The relative errors of the analytical model and the experimental results are less than 10% in all the cases studied in this article.

Active repairs using smart materials such as piezoelectric actuators can play a significant role in reducing the crack damage propagation in engineering structures. This study analytically and numerically investigated the active repair of center-cracked plates using piezoelectric actuators. First, the stress intensity factor (SIF) for a center-cracked plate due to stress produced by a piezoelectric actuator is analytically modeled. This analytical model is obtained by applying the method of weight functions. In the second step, the solution is found for the center-cracked plate due to external loading from known linear elastic fracture mechanics. These solutions are then superimposed, taking into account the superposition principle to yield the total stress intensity factor for the integrated piezoelectric actuator to the center-cracked plate. Finally, the proposed theoretical model is verified by finite element simulation. The results indicated that the relative errors of the analytical model and the FEA results are less than 5% in all the cases studied in this paper.

In this paper, the effect of piezoelectric actuators placed above a circular hole of a rectangular plate subjected to uniform uniaxial tension is studied. The core idea is to investigate the stress (compression/tension) produced by the piezoelectric actuators on the stress distribution around the hole and along the width of the host plate. For this purpose, Finite Element Analysis (FEA) was carried out through parametric study in ANSYS software. The results demonstrated that the positive electric field would decrease and change the state of the stress distribution along the width of the host plate in contrast to the negative applied electric filed which increases the stress distribution smoothly without affecting its behaviour. The results also indicated that the reduction of the stress concentration factor increases with the decrease of the ratio (D/W) for the same applied positive electric field.

Active repairs using piezoelectric actuators can play a significant role in reducing the crack damage propagation in thin plate structures. Mode-I crack opening displacement is the most predominant one in tension, and it is responsible for the failure which in turn affects the load carrying capability of the cracked structure. In addition, there are limited studies that investigated the effect of the piezoelectric actuator over mode-I active repair. In this study, the mode-I stress intensity factor for a plate with a center crack, and a bonded piezoelectric actuator was modeled using the linear elastic fracture mechanics. For this, an analytical closed-form solution is developed using the virtual crack closure technique taking into account mode-I as the only effective mode, coupling effects of the piezoelectric patch, and the singular stress at the crack tip. In addition, the total stress intensity factor was obtained by the superposition of the stress intensity factor obtained from the stresses produced by the piezoelectric actuators on the crack surfaces as the only external loads on the cracked plate and the stress intensity factor due to the far-field tension load. The proposed analytical model for mode-I stress intensity factor was verified by a finite element–based approach using ANSYS finite element software. The results demonstrated a good agreement between the analytical and finite element models with a relative error of less than 4% in all the cases studied. The results illustrated that the piezoelectric patch is efficient in reducing stress intensity factor when an extension mode of the actuator is applied. However, applying a contraction mode of the piezoelectric actuators produced negative strain which increased the stress intensity factor and thus the severity of the cracked structure and could lead to damage propagation.

Research activities on active repairs and stress control of structures using piezoelectric actuators and adhesive bond have received much attention in recent years. The function of the adhesive bond on active repair is to transmit the induced stresses by the piezoelectric actuator to the host structure in order to reduce the stress intensity on the crack front. Assessment of repair performance of adhesive bonds is done based on the transfer of the shear and peel stress concentration in the adhesive layer. In the present work, three dimensional finite element analyses have been carried to understand the effects of adhesive properties on active repair performance of a cracked aluminium plate under mode I. Adhesive efficiency is evaluated by the stress intensity factor (SIF) as a fracture criterion. The results show that SIF varies inversely with the adhesive layer’s shear modulus.

The fracture performance of cracked structures is dominated by singular stress in the crack tip vicinity. In fracture mechanics most interest is focused on stress intensity factors, which describe the singular stress field ahead of a crack tip and govern fracture of structures when a critical stress intensity factor is reached. In the present work linear fracture mechanics is applied in order to obtain the fracture toughness parameters of a cracked plate integrated with piezoelectric actuator under mode I loading. Analytical model was derived to represent the relation between piezoelectric parameters and stress intensity factor and energy release rate. The results indicate that the stress intensity factor decreases linearly with the application of the different piezoelectric actuator voltages.

The piezoelectric actuator has gained popularity over the last few years. Attention has been directed towards the study of their electromechanical response in active repair and the control of damaged structures. This has been made possible through the development of various numerical and analytical techniques for such studies. The shift of focus towards the piezoelectric based approaches has been due to their advantages, which include strategic cost benefits in maintenance, as well as an increase in the life cycle of the repaired structures. Furthermore, adhesively bonded joints are widely used in the manufacturing and repairing of structures in many industries, especially automotive and aerospace engineering. This is due to the requirement for lightweight materials as well as the potential adhesive used to join materials with different characteristics. The piezoelectric actuator has also shown the capacity in controlling and lowering the shear stress concentration and joint edge peel in adhesively bonded joint systems. The structure’s control of stress and repair can generally be viewed as a reinforcement that influences the structure’s damage tolerance. Therefore, the interest of this review is on the applications of the piezoelectric actuators in both structural damage and the bonded adhesive joint system. The specific goal is to recognize the contemporary scientific challenges, including future opportunities.