Grasshopper Optimisation Algorithm

Structural health monitoring (SHM) is being widely evaluated by the aerospace industry as a method to improve the safety and reliability of aircraft structures and also reduce operational cost. Built-in sensor networks on an aircraft structure can provide crucial information regarding the condition, damage state and/or service environment of the structure. Among the various types of transducers used for SHM, piezoelectric materials are widely used because they can be employed as either actuators or sensors due to their piezoelectric effect and vice versa. This paper provides a brief overview of piezoelectric transducer-based SHM system technology developed for aircraft applications in the past two decades. The requirements for practical implementation and use of structural health monitoring systems in aircraft application are then introduced. State-of-the-art techniques for solving some practical issues, such as sensor network integration, scalability to large structures, reliability and effect of environmental conditions, robust damage detection and quantification are discussed. Development trend of SHM technology is also discussed.

Piezoelectric Transducer-Based Structural Health Monitoring for Aircraft Applications.

The birth of smart materials such as piezoelectric (PZT) transducers has aided in revolutionizing the field of structural health monitoring (SHM) based on non-destructive testing (NDT) methods. While a relatively new NDT method known as the electromechanical (EMI) technique has been investigated for more than two decades, there are still various problems that must be solved before it is applied to real structures. The technique, which has a significant potential to contribute to the creation of one of the most effective SHM systems, involves the use of a single PZT for exciting and sensing of the host structure. In this paper, studies applied for the past decade related to the EMI technique have been reviewed to understand its trend. In addition, new concepts and ideas proposed by various authors are also surveyed, and the paper concludes with a discussion of the potential directions for future works.

A Review of the Piezoelectric Electromechanical Impedance Based Structural Health Monitoring Technique for Engineering Structures

Structural health monitoring is an important aspect of maintenance for bridge columns in areas of high seismic activity. In this project, recently developed piezoceramic-based transducers, known as smart aggregates (SA), were utilized to perform structural health monitoring of a reinforced concrete (RC) bridge column subjected to pseudo-dynamic loading. The SA-based approach has been previously verified for static and dynamic loading but never for pseudo-dynamic loading. Based on the developed SAs, an active-sensing approach was developed to perform real-time health status evaluation of the RC column during the loading procedure. The existence of cracks attenuated the stress wave transmission energy during the loading procedure and reduced the amplitudes of the signal received by SA sensors. To detect the crack evolution and evaluate the damage severity, a wavelet packet-based structural damage index was developed. Experimental results verified the effectiveness of the SAs in structural health monitoring of the RC column under pseudo-dynamic loading. In addition to monitoring the general severity of the damage, the local structural damage indices show potential to report the cyclic crack open-close phenomenon subjected to the pseudo-dynamic loading.

Cyclic Crack Monitoring of a Reinforced Concrete Column under Simulated Pseudo-Dynamic Loading Using Piezoceramic-Based Smart Aggregates

The feasibility of tuning the band structure of phononic crystals is demonstrated by employing magnetostrictive materials and applying an external magnetic field. Band structures are calculated with a plane wave expansion method that accounts for coupling between the elastic behavior and the magnetic field through the development of elastic, piezomagnetic, and magnetic permeability effective tensors. We show the contactless tunability of the absolute band gaps of a two-dimensional phononic crystal composed of an epoxy matrix and Terfenol-D inclusions. The tunable phononic crystal behaves like a transmission switch for elastic waves when the magnitude of an applied magnetic field crosses a threshold.

Tunable magnetoelastic phononic crystals

In this paper, a performance-based optimal seismic design of steel frames is presented utilizing Charged System Search (CSS) optimization. This meta-heuristic optimization algorithm has been recently developed and employed in many optimization problems showing a high capability in structural optimization. Here, a pushover analysis method based on semi-rigid connection concept is employed as analysis and design method. Two numerical examples which have been previously considered in literature are studied and the results illustrate significant improvement in structural weight compared to the conventional design methods. The capabilities of the CSS are compared to those of the ACO and GA.

Performance-based seismic design of steel frames utilizing charged system search optimization

We present a structural health monitoring system based on the simultaneous use of passive and active sensing. The passive approach is based on acoustic emission, whereas the active approach uses th...

Multimodal structural health monitoring based on active and passive sensing

In this article, we describe the capability of a nondestructive evaluation (NDE) method at determining the strength of concrete surfaces. The method uses highly non-linear solitary waves (HNSWs) propagating inside a metamaterial in contact with the concrete to be tested. The metamaterial consists of a chain of spherical particles, and is part of a built-in transducer designed to excite and detect HNSWs. The NDE method exploits the dynamic interaction between the metamaterial and the concrete, and the hypothesis is that this interaction depends on the stiffness of the specimen being inspected. In this study, we tested this hypothesis by assembling two kinds of transducer and by casting cylinders with different water-to-cement ratios. The results show that the time of flight of the HNSWs is inversely proportional to the modulus of elasticity of the concrete. Once fully developed, the proposed NDE method may easily assess concrete surfaces.

Nondestructive testing of concrete using highly nonlinear solitary waves

This article presents a nondestructive evaluation (NDE) method to infer the neutral temperature and the axial stress in thick beams. The method relies on the propagation of highly nonlinear solitary waves generated at one end of a chain of spherical particles in a dry point contact with the beam to be evaluated. The waves are reflected back to the chain and the research hypothesis is that the axial stress, which influences the beam's stiffness, affects the amplitude and speed of the reflected waves. To verify this hypothesis a general finite element model of thermally stressed beams was developed and coupled to a discrete particle model able to predict the propagation of the waves along an L-shaped granular medium. The models were validated experimentally to quantify the repeatability of the setup, the sensitivity of the wave features on the thermal stress, and the independence of the wave features on the neutral temperature of the beam. The hypothesis was proven valid by both the numerical and the experimental results. In the future, these findings may be used to refine a NDE method to assess stress in columns, to infer the neutral temperature of continuous welded rails, and to prevent thermal buckling of critical structures.

Axial stress determination using highly nonlinear solitary waves.

We describe a nondestructive evaluation (NDE) method based on the propagation of highly nonlinear solitary waves (HNSWs) to determine the excess of water on the surface of existing concrete structures. HNSWs are induced in a one-dimensional granular chain placed in contact with the concrete to be tested. The chain is part of a built-in transducer designed and assembled to exploit the dynamic interaction between the particles and the concrete. The hypothesis is that the interaction depends on the stiffness of the concrete and influences the time-of-flight of the solitary pulse reflected at the transducer/concrete interface. Two sets of experiments were conducted. In the first set, eighteen concrete cylinders with different water-to-cement (w/c) ratios were cast and tested in order to obtain baseline data to link the ratio to the time of flight. Then, sixteen short beams with fixed w/c ratio, but subject to water in excess at one surface, were cast. The novel NDE method was applied along with the conventional ultrasonic pulse velocity technique in order to determine advantages and limitations of the proposed approach. The results show that the time of flight detected the excess of water in the beams. In the future, the proposed method may be employed in the field to evaluate rapidly and reliably the condition of existing concrete structures and, in particular, concrete decks.

Amir Nasrollahi

Papers

Performance-based seismic design of steel frames utilizing charged system search optimization

Multimodal structural health monitoring based on active and passive sensing

Nondestructive testing of concrete using highly nonlinear solitary waves

Axial stress determination using highly nonlinear solitary waves.

Detecting the Presence of High Water-to-Cement Ratio in Concrete Surfaces Using Highly Nonlinear Solitary Waves