To study the three-dimensional (3D) morphological evolution of damage of the polymer bonded explosive (PBX) during compression process, the damage process of the PBX at the mesoscopic scale was analyzed. Furthermore, the damage evolution of the PBX was also deduced. The 3D deformation behavior and devolution of the internal microstructure of PBX during the in situ compression process were systematically investigated by integrating micro computed tomography (CT) imaging and digital volume correlation (DVC) method. The displacement and strain inside the PBX during the loading of down load were obtained through the DVC method. The results revealed that the strain concentration always appeared at binders between the granules before failure and led to granule internal cracking or granule edge cracking. The results further indicated that integration of micro CT and DVC technique can provide a more practical and effective method for investigating the structural features, strain, and damage mechanism of PBXs during compression process. This study has significant meaning for comprehensive investigation of the damage mechanical behavior of PBX.

Carbon reinforced concrete (in short: carbon concrete) allows thin cross sections and lightweight, high-strength structures. This is demonstrated in this article using the example of a lightweight, prefabricated ceiling girder. In addition to the new building material carbon concrete, another innovative cement-bonded composite material is used: concrete-impregnated nonwovens. The ceiling element is a very light, slim construction that is curved in the transverse direction. In addition to the material and construction, the article describes the experimental investigation and the possibility of calculation using an analytical approach.

This paper treats an experimental study that focusses on optical infrared thermography for non-destructive testing of composites through lock-in and flash excitation. Different fiber reinforced plastics with various artificial defects have been investigated. Three different post-processing techniques are applied, namely fast Fourier transform (FFT), principal component analysis (PCA) and thermographic signal reconstruction (TSR). A comparison between the different excitation and post-processing methods is performed, and their strengths and weaknesses in detecting artificial defects in composites are evaluated and discussed.

It’s difficult to directly measure the pressure on the surface of the material in the impact process. The PVDF (Polyvinylidene Fluoride) gauges may help to solve the problem. In this paper, some split Hopkinson pressure bar(SHPB) experiments were carried out with the PVDF Gauges as specimens. And the strain gauges pasted on the bars are used as measurement method. By comparing the results of the strain gauges and the PVDF gauges, it is proved that there are stress concentration when the PVDF gauges were sandwiched directly in the solid interface. Then two methods to eliminate stress concentration are verified by experiments. The first method is adding cushion, such as electrical tape. The second method is using 502 glue, which is evenly coated on the interface.

In an aircraft engine, some pieces are describing a rotating movement. These parts are in contact with rotating and non-rotating parts through the bearings and gears. The different contact patches are lubricated with oil. During the lifetime of the engine mechanical wear is produced between the contacts. This wear of the bearings and gears will produce some debris in the oil circuit of the engine. To ensure effective operations of the aircraft engines, the debris monitoring sensors play a significant role. They detect and collect the debris in the oil. The analysis of the debris can give an indication of the overall health of the engine. The aim of the paper is to develop, design and model an oil test bench to simulate the oil lubrication circuit of an aircraft engine to test two different debris monitoring sensors. The methodology consists of taking inspiration of the oil lubrication system of the aircraft engine. The first part is to build the oil test bench. Once the oil test bench is functional, the tests of the two debris monitoring sensors are performed. A test plan is followed, 3 sizes of debris, like the type and sizes of debris found in the aircraft engine oil, are injected in the oil. The test parameters are the oil temperature, the oil flow rate and the number or mass of debris injected. Each time debris are injected, they are detected and caught by the two sensors for a temperature and a flow rate for which the sensors have been optimized. The test results given by the two sensors are similar to the mass and number of debris injected into the oil circuit. The two sensors never detect the total mass of debris injected in the oil. In average 55 to 60 % of the mass injected are detected and caught by the two sensors. The sensors are very efficient to detect the debris which size correspond to the design range parameters of the sensors, but their efficiencies fall in detecting debris which size lies outside this range.

The rupture process in brittle materials is associated with tensile stresses at microscopic flaw scale inside their volume. Acoustic emission monitoring of diametral compression tests is an adequate option to assess the progression of damage. An improved algorithm for AE sources localization with P-wave velocity, v_p, calculation and an enhanced methodology for P-wave onset time, called CLAPWaVe [1], is applied to analyze the distribution of damage and the evolution of stiffness within monzogranite specimens. Complementary analyses allowed the identification of four zones of damage accumulation within the specimen volume, each of them with different cracking levels, absolute energy release, E_A, associated v_p values, induced by different phenomena occurring during the loading process. The observed non-homogeneous damage distribution confirms that using a unique v_p value to perform the localization of all AE sources, as usually adopted, is not representative of the real condition of the specimen.

The accurate characterisation of pressure loads imposed on structural members following the detonation of a high explosive is critical to our ability to design protective systems. This poses serious challenges for experimentalists, due to the high magnitude and short duration of loading. If the distance from the detonation to the target is relatively large, the loading is imparted through the interaction of a shock wave travelling away from the detonation through the surrounding medium, say air. Here, pressure magnitudes are typically in the range 10³-10⁶Pa and are measurable using conventional, commercially available piezo-electric or piezo-resistive pressure transducers. A considerable effort has been expended on experimentally characterizing these “far-field” loads and consequently, we have a strong understanding of the mechanisms and magnitudes of loading. However, we are also interested in the loading when the target is very close to the detonation, for a range of protection applications, from aviation security to the design of personnel protection. Here, very different physical processes dominate. At these so-called “near-field” distances from a detonation (<~1m/kgTNT^1/3) the high temperature gaseous detonation products are still violently expanding, and loading on a target is generated by the impingement of both the shocked surrounding material and these products themselves. Blast pressures are often higher that the yield strength of structural materials and temperatures can reach several thousand Kelvin. Furthermore, loading can vary by an order of magnitude over very short distances and timescales. This paper will describe experimental work conducted at University of Sheffield on developing approaches to accurately measure and predict near-field blast loading and gain a better understanding of the underlying mechanisms of loading. The challenges inherent to this field of work will be discussed and an attempt made to identify some of the emerging themes for future research.

The flexure inspection of printed circuit boards during assembly and operation is the object of the article. The goal is to identify high stresses which can lead to destruct especially the soldered connections during final product operation using strain gauge technique. This is demonstrated on some examples. It is shown how important is the proper wires installation leading from strain gauges to measurement unit. The tests are performed according IPC guidelines but some remarks are given to guidelines specification.

A combination of Fringe Projection (FP) and 2D Digital Image Correlation (2D DIC) using a single camera has been employed to simultaneously measure in-plane and out-of-plane displacements during different dynamic events such an impact and a vibration analysis. This approach has been adopted in the past by several authors, including Mares et al. [3] who highlighted that if a telecentric lens are not employed the combination of both techniques is not straightforward since the in–plane displacements measured with 2D DIC are sensitive to the out-of-plane displacements. Thus, in-plane displacements measured using 2D DIC should be corrected using the out-of-plane displacements inferred using the FP technique. In the current work, an easy method for in-plane displacement correction [4] using Fringe Projection is adopted when measuring the 3D displacements during an impact on an aluminum plate and the vibration of a composite component which have not been studied by other authors previously.

Vibration-based damage identification can constitute a successful approach for Structural Health Monitoring (SHM) of civil structures. It is a non-destructive condition assessment method, dependent on the identification of changes in the modal characteristics of a structure that are related to damage. However, the damage identification from the modal characteristics of existing structures currently suffers from a low sensitivity of eigenfrequencies and mode shapes to certain types of damage. Furthermore, the sensitivity of eigenfrequencies to environmental influences may be sufficiently high to completely mask the effect even of severe damage. Modal strains and curvatures are more sensitive to local damage, but the direct monitoring of these quantities is challenging when the strain level is very low. In the present work, the identification of the modal strains of a pre-stressed concrete beam, subjected to a progressive damage test, is performed. Dynamic measurements are conducted on the beam at the beginning of each cycle and its response is recorded with multiplexed Fiber-optic Bragg Grating (FBG) strain sensors. Bending, lateral and torsional modes are accurately identified from dynamic strains of the sub-microstrain level. The evolution of the modal characteristics of the beam after each loading cycle is investigated. Changes of the eigenfrequency values, the amplitude and the curvature of the strain mode shapes are observed. The changes in the strain mode shapes appear at the locations where the damage is induced, and are already identified from an early damaged state.