In this paper the pressure waves generated in a test rig previously presented by the authors for the experimental analysis of concrete slabs subjected to blast loading are analysed. To this aim, the concrete samples are replaced by one single aluminium slab instrumented with pressure gauges. In order to analyze the experimental scatter, the test set-up is repeated four times, with the only variation of the location of the aluminium slab within the four available positions in the test rig. The pressure histories registered show good agreement with the typical patterns expected in open-air explosions and demonstrates the quasi-planar shape of the pressure wave acting on the slabs. By comparing between the results obtained in different detonations, the explosive charge seems to be among the main sources of experimental scatter in this kind of tests.

The shear properties evaluation on existing unreinforced masonry structure is usually performed through destructive tests. However, these tests have the characteristics of being very expensive and require significant damage not only on the samples but also on the portion of wall surrounding them. The present work illustrates the design of a new testing procedure for the characterization of the shear properties in masonry panels for application in routine testing. In the aim of preserving the integrity of the area under testing and to reduce the cost of the new testing procedure, it has been decided to use flat jacks. The numerical analyses used to design the test are presented as well as the results of a first application of the procedure.

In order to assess the integrity of welded structures, it is important to accurately know the material characteristics of the weld regions. A weldment is heterogeneous i.e. strength properties vary at different locations within the weld. This influences the behavior of the structure when it is subjected to loading. Hence, the evaluation of material properties within the weld region plays a pivotal role in structural integrity assessment. Traditionally, tensile tests provide constitutive properties like tensile strength and yield strength along with stress (σ) – strain (ε) curves. Alternatively, hardness indentations are also used to procure strength properties of a material. Several transfer functions have been formulated to convert hardness values to strength properties. The validity of these transfer functions with the presence of strength variations is questionable, as these relations do not consider the aspect of heterogeneity. Accordingly, in this research, a heterogeneous weld was considered to assess the relation between Vickers hardness (HV5) and strength properties. Two tensile test configurations were considered – All Weld Metal Tensile Tests (AWMTT) and Micro Tensile Tests (MTT). While AWMTT provides average weld stress-strain properties, MTT provide local properties. These results help to validate the hardness transfer functions and thus calibrate them appropriately. Hardness maps were obtained on polished weld macrographs. The material properties obtained from three methods were compared and significant variations were observed. Based on these differences, an experimentally calibrated transfer function is implemented. With this relation, it is possible to predict weld behavior more accurately and appropriately using hardness maps and tensile tests.

The use of high strength steels (HSS) allows designing lighter, slenderer and simpler structures with high structural performance. In general, the use of HSS leads to weight reduction of the whole structure, which compensates the higher cost of such a material comparing to the conventional construction steels. Knowledge of the fatigue resistance of material plays the key role during design and maintenance of the bridge structures. This contribution brings a comparison of the fatigue crack growth resistance of S355 J0 steel. Differences in microstructure and the texture of material structure could generally play a role in the fatigue crack growth. This study shows that in the case of studied steel texture of material structure has an influence on material fatigue behavior in Paris’ law regime.

This contribution presents the results of an experimental and numerical campaign evaluating the influence of cut-outs on the strength and stiffness of composite timber I-joists. These cut-outs are often introduced in the webs during the instalment of utility lines. The presence of these cut-outs will have an impact on the structural behaviour of the element. However, these influences are not taken into account in the current design standards. In order to evaluate the impact of the cut-outs, an experimental campaign was set up in which the structural behaviour of seven composite I-joist beam was analysed. The geometry and spacing of the cut-outs were varied along these seven beam elements. The experimental results clearly show the reduction in stiffness and the influence on the failure mechanism of the beam elements caused by the cut-outs. Additional to the experimental study, a numerical campaign in which the structural response of these I-joists is modelled is also performed. Nonlinear material behaviour is taken into account in the numerical models through the use of a gradient-enhanced damage model. Overall, good agreement is reached between the experimental and numerical data for the beam elements in the linear elastic regime. The ultimate load was also represented well by the numerical model for those elements which fail due to failure of the hardboard web.

Due to their superior physical and electro-mechanical properties, Carbon Nanotubes (CNTs) are one of the most promising composite fillers to realize ultralight and flexible strain sensors that can be used, among others, to monitor strain concentrations within a structure when damage occurs. In this study, sensors are made of Multi-walled Carbon Nanotubes (MWNTs) embedded in a Polymide (PI) matrix. Nanocomposites are characterized under no-load to study the electrical properties, and under tensile loading conditions, to evaluate the electromechanical and piezoresistive response. The results highlight a two orders of magnitude decrease in electrical resistivity if compared with previous studies, the capability to instantaneously respond to unpredictable deformations and to easily adapt to three-dimensional shapes.

The beauty of the as conceived nanocomposite film, if compared with the commercially available strain gages, is its unprecedented potential expandability to monitor larger areas without the loss of ultra-low local (in scale) detection. Local detection is in fact allowed by nanoscale morphology changes that induce changes in local electrical conduction. The selected polyimide matrix allows the use of the proposed sensor to harsh and high temperature environments while keeping high flexibility and excellent mechanical properties, key parameters for the realization of reliable electromechanical films.

We present the development of a contactless laser ultrasound system for nondestructive inspection of CFRP complex structures. Ultrasound are generated by a thermoelastic effect resulting from a green pulsed laser insulating a point of the inspected part. The resulting displacement of the surface point is probed by a two-wave mixing based interferometer working in the near infrared. The system is flexible and completely fiber-coupled. It is able to provide C-scans on complex shaped CFRP aeronautical structures.

This paper discusses a method for eliminating geometric optics errors that can occur when combining three-dimensional thermal images using hybrid digital holography. We obtained reconstructed digital holography using phase detection autofocus technique and arbitrary tilt plane correction.

In this paper, for nondestructive and quick investigation of the dynamic elastic modulus of PBX, a measurement system based on ultrasound velocity technique has been presented. The accuracy and reliability of the dynamic elastic modulus calculated by the velocity of ultrasonic longitudinal and transverse wave, which synchronizing received and transmitted by a new integrated sensor have been studied. Thermal cycling tests of different formulations of PBX, HMX and TATB based PBX, are undertaken at the scope from -54～74℃. Dynamic elastic modulus is measured by the nondestructive measurement system to compare with static elastic modulus. The results show that dynamic elastic modulus, dynamic/static elastic modulus ratio reflect the difference of mechanical properties and material consistency. Dynamic elastic modulus quickly decreases to a low value and vibrates as the thermal cycling being in progress and mechanical properties decrease to a lower degree. After resting for a month, dynamic elastic modulus recovers in some degree along with mechanical properties. At preliminary stage of the thermal cycling, dynamic/static elastic modulus ratio increases and material consistency decreases, with micro-defects’ initiation, as cracks and voids et. Along with the increase of the thermal cycling, dynamic/static elastic modulus ratio decreases on the contrary. PBX recovers consistency, with micro-defects’ self-healing, in a lower level of mechanical properties.

Source localization techniques assume that elastic wave velocity distributions are homogeneous in many cases. However, the assumption would be violated if objects are locally and heavily damaged, and accuracies of identified source locations by the source localization techniques are consequently degraded on the heterogeneity. The authors proposed a source localization technique for overcoming the difficulty by adopting ray-trace technique to properly consider the heterogeneity of the elastic wave velocity distributions, and the relay point is introduced to raise accuracy of the identified source locations as well in the source localization technique. The source localization technique has been implemented in an algorithm of AE-Tomography and successfully contributed to identify elastic wave velocity distributions by using arrival times of elastic waves at receivers. The resolution of the identified source locations depends on densities of the relay points in the source localization technique, and it immediately implies that the relay points have to be finely installed in the objects of interest to raise the resolution of the source locations on objects of interest. Since the computational costs of the source localization technique depends on the total number of nodal and relay points on the objects, the computational costs drastically rise if it is intended that the source locations are identified in high resolution. The resolution of the identified source locations influences accuracies of identified elastic wave velocity distributions, and the degradation of the accuracies consequently degrades the accuracies of identified elastic wave velocity distributions. For overcoming this difficulty, the authors proposed a source localization technique that installs source candidates finely only in the vicinity of roughly estimated source locations. Nevertheless, this technique reduces the computational cost in comparison with the conventional source localization technique based on ray-trace techniques, it still expensive if the range of “the vicinity” is enlarged and the number of events is large. Thus, a new source localization technique is introduced in this study. The technique installs the source candidates finely in smaller region in comparison with the previously proposed technique. The region is moved and its size is changed adaptively in the computational procedure to raise the accuracy of the identified source locations. This procedure requires iterative computations for convergence. However, its total computational cost is reduced because the number of relay points is smaller and the cost for the ray-trace is reduced. The proposed technique verified by performing a series of numerical investigations and its capability is discussed. The results of the investigations suggested that the proposed source localization technique identifies the source locations of elastic waves accurately on the heterogeneous elastic wave velocity distribution. It is also confirmed that the accuracy of the identified source locations is controllable by changing parameters for the convergence and computational cost is reduced in comparison with the previously proposed technique.