Numerical calibration of an easy method for seismic behaviour assessment on large scale of masonry building aggregates

The paper deals with the numerical calibration of a speedy procedure for large scale seismic vulnerability assessment of masonry building aggregates, which are typical building compounds diffused within historical centres of many Italian towns. First of all, based on several numerical analyses developed with the 3MURI calculation program, this simplified assessment procedure has been implemented, it being derived from the well known vulnerability form for masonry buildings integrated by five parameters accounting for the aggregate conditions among adjacent units. Later on, the set-up procedure has been validated through an application to a single building aggregate in the Vesuvius area. Since the results previously achieved have been again confirmed, subsequently the procedure has been used to investigate a wide area of the historical centre of Torre del Greco, allowing for the knowledge of the buildings most at risk under earthquake.Finally, the methodology has been applied to the historical centre of Poggio Picenze (AQ), damaged by the recent Italian earthquake (2009), in order to prove its effectiveness to foresee the damage level experienced by other types of masonry aggregates under seismic actions.     

Real-time identification of disaster areas by an open-access vision-based tool

Structural damages caused by natural catastrophic events cover a wide area and it is convenient to supervise the event consequences by vision tools. The aim of this paper is to supply a rapid damage detector designed as a way to aid in risk assessment, damage control and disaster prevention as well as a way to speed the examination of catastrophic effects for emergency studies. The satellite pictures covering the area of interest represent the required bits of information to manage the developed telematics tool. A case study is discussed in order to provide experimental evidence of the proposed procedure potential. Moreover, a multi-view image/video fusion system is integrated in the image process to detect the damage levels of structures to overcome the limitations on the vertical information provided by a satellite. In synthesis, this study shows how a GIS-based real time monitoring system can be effectively used for a rapid evaluation of structural damage and disaster management.     

Improved Complex-valued Radial Basis Function (ICRBF) neural networks on multiple crack identification

This paper introduces a new class of neural networks in complex space called Complex-valued Radial Basis Function (CRBF) neural networks and also an improved version of CRBF called Improved Complex-valued Radial Basis Function (ICRBF) neural networks. They are used for multiple crack identification in a cantilever beam in the frequency domain. The novelty of the paper is that, these complex-valued neural networks are first applied on inverse problems (damage identification) which come under the category of function approximation. The conventional CRBF network was used in the first stage of ICRBF network and in the second stage a reduced search space moving technique was employed for accurate crack identification. The effectiveness of proposed ICRBF neural network was studied first on a single crack identification problem and then applied to a more challenging problem of multiple crack identification in a cantilever beam with zero noise as well as 5% noise polluted signals. The results proved that, the proposed ICRBF and real-valued Improved RBF (IRBF) neural networks have identified the single and multiple cracks with less than 1% absolute mean percentage error as compared to conventional CRBF and RBF neural networks, mainly because of their second stage reduced search space moving technique. It appears that IRBF neural network is a good compromise considering all factors like accuracy, simplicity and computational effort.     

聚合醇低伤害压裂液探索研究

水力压裂是低渗油气田油井增产、水井增注的的重要措施之一。为了降低压裂液对储层伤害,进行水基聚合醇压裂液基础配方研究。选择有机硼作为交联剂,通过室内实验确定了压裂液的最佳配方:聚合醇质量分数为1.8%、交联剂质量分数为0.9%、pH值调节剂质量分数为0.16%,参照SY/T 5621—1993《钻井液测试程序》评价压裂液性能。评价结果表明,该压裂液具有较好的流变、抗剪切和破胶性能,残渣含量低,对储层伤害小于常规压裂液。为油气田开发增产提供了有效技术支撑。     

Dynamic responses and damage analyses of tunnel lining and errant large vehicle during collision

Collision accidents between errant vehicles and tunnels occur frequently, causing serious loss of life and property as well as the damage to the tunnel lining. Damage analysis of the tunnel lining under collision loads is still a lack of research at present. Based on dynamic finite element method, this study simulates and analyzes the interaction between errant large vehicles and tunnel lining structure and their dynamic response processes under various collision cases. It is noted that the lining structure mainly suffers tensile damage and its value increases with the increases of the collision angle and the vehicle speed. The larger the vehicle speed and the collision angle are, the bigger accelerations the passengers experience. A series of in-situ damage detections and sampling tests of the tunnel lining in a real collision accident that occurred in the Panlong Tunnel on Jinghu Highway in China in 2009 strongly approve the numerical simulation results. This study provides technical supports to the optimal design and operations management of tunnels.     

按照国标的光学薄膜损伤阈值测试装置

按照ＩＳＯ／ＤＩＳ１１２５４ 光学表面激光损伤阈值测量标准和等价国标的要求,建立了薄膜的１μｍ ＹＡＧ脉冲激光损伤阈值定量测试装置,对脉冲能量、脉冲持续时间、光束分布及相应的不确定度均进行了测试。     

The Master SN curve approach – A hybrid multi-scale fatigue simulation of short fiber reinforced composites

Typical short fiber reinforced composites (SFRCs) components have a different statistical distribution of orientation of fibers at different points leading to different static and fatigue behavior at different locations across the component. To link component-scale calculations with this variability of fiber orientations, each element in the FE model is modeled as a Representative Volume Element (RVE); the static and fatigue properties must be calculated for each of these elements. While there are established methods to estimate the static properties, there are none for the fatigue properties. A hybrid (combination of micromechanics and tests) and multi-scale (damage in micro-scale linked to macroscale fatigue properties) method of predicting the SN curve for every point in a short fiber composite has been developed. This proposed method is based not only on tests but on a combination of manufacturing simulation, tests and multi-scale mechanics. An extensive test program was undertaken to study the fatigue behavior of short fiber composites and validate the concept of the Master SN curve (MSNC) approach. The MSNC approach is compared with two prevalent approaches – strength based scaling and test based interpolation. The MSNC approach was found to be in a good agreement with the experimental results and was confirmed to be more accurate than the prevalent methods.     

A quasi-static indentation test to elucidate the sequence of damage events in low velocity impacts on composite laminates

Any attempt to achieve composite laminates with improved damage tolerance to low velocity impacts must depart from the understanding of the sequence of damage mechanisms taking place. To this purpose, a series of quasi-static indentation experiments was conducted on AS4D/TC350 carbon/epoxy specimens. The induced damage at different indenter displacements was characterized using electron microscopy and C-scan, while the residual indentation profiles were captured with a 3D surface roughness machine. The indentation depth was shown to have relaxed after the test, reaching a steady value after 14 days. For the conditions explored, the relaxation was not dependent on the damage extent. The results showed that matrix cracking is in fact the crucial damage mechanism as it is responsible for the first sudden loss of load capacity and triggers the progressive growth of delaminations.     

Effect of voids on the crack formation in a [45/−45/0]s laminate under cyclic axial tension

In the present work, the influence of manufacturing induced voids on damage mechanisms at the microscopic scale was analysed on [45/−45/0]_s laminates subjected to tension fatigue loading. Microscopic observations of the top surface of the 45° ply revealed that the first event of damage at the microscopic scale was the initiation of multiple micro-cracks in the matrix between the fibres, located preferentially in correspondence of the voids in that layer. The subsequent coalescence of these micro-cracks gave rise to the formation of a crack propagating in the 45° fibres direction. This is qualitatively the same scenario observed in void-free specimens in a recent work by the authors, thus confirming that the same crack initiation criterion can be applied in the absence and presence of voids. In addition, the micro-scale damage is shown to evolve faster and therefore off-axis cracks to initiate earlier and in a larger quantity in the presence of voids.     

Strength and damage tolerance of composite–composite joints with steel and titanium through the thickness reinforcements

Today’s aeronautic, automotive and marine industry is in demand of structurally efficient, low weight alternatives for composite–composite joints which combine the advantages of low weight input of adhesively bonded joints and high damage tolerance of through the thickness bolted joints. In the present work, composite–composite joints are reinforced through the thickness by thin metal inserts carrying cold metal transfer welded pins (CMT pins). The influence of pin alignment and type of pin on the damage tolerance of single lap shear (SLS) composite–composite joints is investigated. The use of titanium reinforcements is evaluated and compared to stainless steel reinforced, adhesively bonded and co-cured specimens. A detailed analysis of the stress–strain behavior is given and the stiffness and energy absorption of the SLS joints during tensile loading is assessed. The results show that joints reinforced with CMT pins absorb significantly higher amounts of energy, when compared to adhesively bonded and co-cured joints.