In modal identification, the value of the model parameters and the associated uncertainty depends on the quality of the measurements. The maximum likelihood estimator ($mle$) is a consistent and efficient estimator. This means that the value of the parameters trends asymptotically close to the true value, while the variance of such parameters is the lowest possible with the associated data. The $mle$ implementation and application can be complex and generally need strong computational requirements. In applications where the number of inputs and outputs are elevated (as in modal analysis) is common to reduce the covariance matrix to a diagonal one where only the variances are considered. This implementation is still consistent but not efficient. However, it generates acceptable results.
The current work shows that using efficiently the output information as complement to the input--output relations, it is possible to improve the model identification reaching similar levels than the $mle$, while reducing the execution time and the computational load.

A super-pressure balloon (SPB) is a vehicle which can fly at a constant altitude for an extended period to perform scientific observations at a fraction of the satellite cost. The balloon is always pressurized to keep its volume constant, which suppresses buoyancy fluctuation due to the difference of internal gas temperature between day and night. We have been developing a lightweight, high strength balloon made of thin polyethylene films and diamond-shaped net with high tensile fibers. Although previous research shows that the tensile strength of the net meets the requirements as a strength member of the SP balloon, the net covering the SP balloons are sometimes broken at its inflation test. It is considered to be due to non-uniform expansion which causes stress concentration, however, there is no method to confirm this hypothesis. In this study, we have developed a simplified digital image correlation (SiDIC) method using the intersection detector, which allowed us to track the diamond-shaped weave of the net to measure the balloon deformation during the pressurization process. Digital image correlation (DIC)—an optical method to measure changes in images—usually requires black spots on the specimen for its analysis. However, such method is not suitable to study the shape of SP balloons, as ink spots on the thin film may affect its strength and weight properties. Thus, we developed this SiDIC approach, which overlays the intersection detector to the DIC. This made it possible for the program to track intersection points on the net without using the ink spots. First, this new method was tested using a rubber balloon covered by black patterns and a diamond- shape polymer net. A series of pictures of the balloon as inflated by air at a constant rate were taken and the deformation was measured using the DIC and SiDIC method to compare the results. From the results, the SiDIC almost agree with the result by the DIC method. The error between the DIC results and the real deformation were 87%, and the error between the SiDIC results were 84%. Next, to identify whether the DIC and SiDIC method can be used on the SPB, a rubber balloon covered just with a diamond- shape polymer net was used. In this test, the DIC method could not measure the deformation accurately and had an error of 56% between the real deformation, whereas the SiDIC had an error of 83%. Therefore, the SiDIC method is suitable for monitoring the deformation of the SPB.

This study deals with the development of the knowledge about steel-reinforced concrete (RC) beams that are externally reinforced with textile reinforced concrete (TRC). During the last decades, TRC has been a subject of research, but few authors studied the use of TRC for a reinforcement of structural elements under fire or under combined elevated temperatures and mechanical loading. Reinforcement and protection of structures by a TRC solution under fire have got much potential but this subject is still not well studied. In this research, some aspects about the interaction between the TRC and reinforced concrete structure were numerically investigated in order to optimize the potential of TRC in fire-structural purposes.

Assessment of the residual strength of reinforced concrete buildings subjected to fire is a problem that many times requires a very fast resolution that is necessary for the action of firemen and/or for forensic fire investigation and/or structural assessment of post-fire condition of the building: in all cases safety and integrity of firemen and researchers can be at risk, and it is necessary to have quick and sufficiently reliable information in order to choose whether enter freely, enter with caution or simply do not enter the burned structure, so there is no time or background to develop mathematical models of damage propagation and/or of the structure. This work presents an experimental methodology for a fast assessment of post-fire residual strength of reinforced concrete frame buildings based on the high correlation between the loss of strength and non-destructive tests results of frame concrete elements subject to fire action.

This study aims to a better understanding of the performance of a shock tube used to produce blast loading in controlled laboratory environments. Special focus is placed on the influence of the diaphragm failure process on the blast wave formation in the tube. Experimental observations are supported by numerical simulations in an attempt to obtain more insight into the underlying phenomena. It was found that the diaphragm failure process introduces a multi-dimensional flow field downstream the diaphragms. This is observed as a loss of directional energy in the distant flow field and therefore affects the reflected overpressure on blast-loaded plates located at the rear end of the tube. These findings provide important insight into how such a facility works, especially if the dynamic response of flexible plates is of interest.

In this paper, mechanical experiments with a low-cost interferometry set-up are presented. The set-up is suitable for an undergraduate laboratory where optical equipment is absent. The arrangement consists of two planes of illumination, allowing the measurement of the two perpendicular in-plane displacement directions. An axial load was applied to three different metals, and the longitudinal and transversal displacements were measured sequentially. A digital camera was used to acquire the images of the different states of the load of the illuminated area. A personal computer was used to perform the digital subtraction of the images to obtain the fringe correlations, which are needed to calculate the displacements. Finally, Young's modulus and Poisson's ratio of the metals were calculated using the displacement data.

The objective of this study is to measure the interstitial pore pressure into saturated concrete under hundreds of Mega-Pascal of confinement. This study is carried out within a more general context aiming to understand the behavior of concrete structures under impact. It is well known that the water saturation in massive concrete structures evolves from quasi-dry state at the surface to reach a quasi-saturated state at the core. Since the response of these structures under impact is highly linked to the state of saturation into the material, there is a suspicious that the pore pressure plays a major effect. This paper presents a new testing technic developed to measure the concrete pore pressure at high confining pressure. This latter is generated by means of a high capacity GIGA press. The new concept consists in implementing a pressure sensor into a water collecting cap. This cap is designed specially to collect water from concrete subjected to mechanical confinement pressure. Experimental results show that concrete pore pressure can reach values of the order of the confining pressure

Recently, there is an increasing demand for bio-absorbable coronary stent to promote recovery after operation. A magnesium alloy stent is one choice because of its biodegradable property. However, magnesium alloys have lower rigidity and lower ductility than other metals, so that an appropriate concept on designing stent structure is required to secure the radial rigidity. In this study, design parameters to actualize the AZ31 magnesium alloy stent with sufficient radial rigidity were investigated. First, the necessary radial rigidity was investigated by the comparable tests of commercially available stents. Next, the design parameters of cell struts were selected and the optimum values of the parameters to achieve the high radial rigidity were investigated by means of elastic-plastic finite element analysis. Finally, the trial model based on the optimized design parameters was produced and it was confirmed that the model had enough radial rigidity with no fracture during crimping and expansion processes.

Metals with a fine-grained microstructure have exceptional mechanical properties. Severe plastic deformation (SPD) is one of the most successful ways to fabricate ultrafine-grained (UFG) and nanostructured (NC) materials. Most of the SPD techniques employ very low processing speeds. However, the lowest steady-state grain size which can be obtained by SPD is considered to be inversely proportional with the strain rate at which the severe deformation is imposed. In order to overcome this limitation, methods operating at higher rates have been envisaged and used to study the fragmentation process and the properties of the obtained materials. However, almost none of these methods, employ hydrostatic pressures which are needed to prevent the material from failing at high deformation strains. As such, their applicability is limited to materials with a high intrinsic ductility. Additionally, in some methods the microstructural changes are limited to the surface layers of the material. To circumvent these restrictions, a novel facility has been designed and developed which deforms the material at high strain rate under high hydrostatic pressures. Using the facility, commercially pure aluminum was processed and analysis of the deformed material was performed. The microstructure evolution in this material was compared with that observed in static high pressure torsion (HPT) processed material.

This work is motivated by increasingly used of composite structures under severe loading conditions. During their use, these materials are often subjected to impact as for example, in the aeronautical field the fall of hailstone on structure composites. In fact, the low energy traditional impact tests don’t allow to see the evolution of the damage and don’t permit also to compare the best tolerance to impact between different stratifications. The multi-impact tests made it possible to find a solution to this problem. In this work, multi-impact tests are performed on three carbon / epoxy stratifications. The final goal is to predict the durability of the composite structures during impact loading for their design.

This study brings to light the response of multi-impact tests through force-time and force-displacement curves obtained experimentally. On the other hand, a parameter D has introduced following the experimental results. This made it possible to rank the three stratifications from their tolerance to multi-impact tests. To evaluate the post impact damage, ultrasonic testing techniques are used. The results allow to find the relationship between the damaged surface obtained by the ultrasonic control and the parameter D and to rank the three laminates configurations.