The study of the bond behaviour between fibre-reinforced polymer (FRP) systems and concrete is an issue that nowadays attracts many researchers. The scientific community dedicated to the research of FRP reinforcement has been conducting numerous experimental programmes aiming to assess the local bond–slip law of the FRP–adhesive–concrete connection. This paper reports the relevant results obtained by the Structural Composite Research Group of Minho University in the scope of an international Round Robin Test. The suitability of the recommended test setup to derive a local bond constitutive law for modelling the bond behaviour of near-surface mounted reinforcement systems is discussed based on a deep interpretation of the results.

The lifetime prolongation of the old industrial structures is an important economic issue. Damage detection techniques can be helpful to warn about any structural deterioration and to assure sufficient time for counteraction activities. In the paper, the results of strain measurements on scaled leg model of offshore oil platform with different damage cases are presented. The considered damage cases were yielding, chord cutting and brace–chord detachment located in the bottom part of the model. Yielding was detected mainly by the sensors located in the lower part of the structure. On the other hand, brace–chord detachment was detected by all sensors on the structure. Therefore, the global character of the considered damage indicator is proven at least for some important class of damage cases. Due to transient response during brace–chord detachment and interpretation problems of results for partial chord cutting, the necessity of continuous monitoring was evident. The time point of detachment occurrence can be easily detected using difference or cross-correlation technique. The change in static-strain levels together with the detection of transient signal seems to be a simple and an effective damage indicator based on interrogation of thermo-mechanical strains.

This paper experimentally investigates the crash responses of the empty and polyurethane foam-filled conical tubes with shallow spherical caps under quasi-static axial loading. To find more details about the energy absorption mechanism, finite element methods is used to simulate the crush process. In terms of finding more efficient and lighter crash absorbers particularly, the energy absorption and specific energy absorption and load ratio have been considered. The influences of the tube geometrical and material parameters such as radius of spherical region, wall thickness, length, semi-apical angle and foam density on the energy absorption mechanism have been investigated. This study provides practical information for the use of thin-walled tubes with shallow spherical caps as energy absorbers in aerospace applications to design reentry of sounding rocket based on foam-filled conical tube with shallow spherical caps.

The accuracy of biomechanical simulation has been improved by using high-resolution computed tomography (CT) to define the geometry and material parameters. This technique has been used to assess numerous systems, including the mechanical properties of bone, fixation techniques post-fracture and the performance of bone microarchitecture. In this study, a semi-automated process for converting CT data into finite element (FE) models was used to model the mid-shaft (diaphysis) of porcine femoral samples under sub-maximal torsional and compressive load. Physical validation was undertaken to investigate if the all-important geometry and material property mapping functioned correctly. Porcine femoral specimens were imaged using contiguous helical CT, which was converted to FE models using ScanIP from Simpleware, Exeter, UK. The heterogeneous material properties were estimated using density–elasticity relationships proposed in literature for human bone samples. Laboratory testing performed favourably, with a linear strain response validating the use of the array of linear material models used in simulation. The simulation procedure also performed well. Linear regression and mean error calculation demonstrated accurate correlation between predicted (from simulation) and observed (measured within the laboratory) results that offered improvement over the accuracy within comparative testing for human samples. Using FE modelling on a patient-specific basis offers potential in a number of scenarios, including the determination of injury risk and design of protective equipment. The increased accessibility of animal samples allows large-scale fracture testing of complex loading mechanisms and the potential to consider younger animal samples (to investigate the behaviour of developing bone). Spiral fractures of long bones have been demonstrated to be an indicator of non-accidental injury in children. Combining the increased accuracy in torsional simulation in this study with younger sample testing may be employed to attempt to determine the causes of fracture from post fracture scans, aiding in the diagnosis of non-accidental injury.

Marciniak–Kuczynski and Nakajima tests of the dual-phase steel Docol 600DL (www.ssab.com/) have been carried out for a range of stress-states spanning from uniaxial tension to equi-biaxial tension. The deformation histories of the specimens have been recorded by digital images, and the displacement and strain fields have been determined by post-processing the images with digital image correlation software. The fracture characteristics of the material are presented by means of the stress triaxiality, the Lode parameter and the equivalent strain. These parameters are evaluated on the surface of the specimens based on the optical field measurements and assumptions regarding the mechanical behaviour of the material. Additionally the minor versus major principal strains up to fracture are presented. It is found that the material displays a significantly lower ductility in plane-strain tension than in uniaxial tension and equi-biaxial tension, and that it, in the tests exposed to local necking, undergoes large strains between the onset of necking and fracture. Fractographs of selected specimens reveal that fracture is due to growth and coalescence of voids that occur in localised areas governed by shear-band instability.

Digital Image Correlation algorithms capable of determining continuous displacement fields are receiving growing attention in the field of mechanical properties identification. In this paper, we develop an Improved Spectral Approach (ISA) to reconstruct continuous displacements based on their Fourier decomposition. This approach leads to a time and memory-efficient algorithm, thanks to the fast Fourier transform. Moreover, the Fourier-based decomposition enables accurate heterogeneous measurements. Improvements consist in increasing the accuracy and convergence rate as well as dealing with non-periodic displacements and images. Furthermore, a theoretical framework is presented to quantify the noise sensitivity of the ISA from which useful information is retrieved. The approach is evaluated using synthetic images deformed by heterogeneous displacement fields. Comparisons show that the introduced modifications lead to lower uncertainties by one order of magnitude in the case of non-periodic images and displacement field studied. Moreover, first-order (SO1) and second-order (SO2) subset-based Digital Image Correlation algorithms are compared with the ISA. The comparisons herein reveal that the uncertainties of the ISA are 6–9 times smaller than those of the SO1 due to insufficiency of the first-order shape function for the estimation of heterogeneous displacements, while being slightly smaller than those of the SO2. Moreover, as the image smoothness decreases, the uncertainties of the SO2 deviate from those of the ISA and the exact displacements. The presented approach shows great potentials for challenging applications such as strain measurements at microstructural levels.

The material degradation of concrete subjected to fire events has a severe influence on the load-carrying capacity of support structures. Spalling of concrete layers, exposing the reinforcement bars and degradation of the material properties (Young's modulus, compressive strength) may lead to significant damage of the reduced cross-section and, therefore, cause failure of the structure. In order to understand the stress build-up at the heated surface caused by thermal expansion due to fire loading, finally leading to damage and spalling of concrete, the strain behaviour of cement paste and concrete exposed to combined thermo-mechanical loading is the focus of this work. Hereby, the evolution of thermal strains, Young's modulus and Poisson's ratio with increasing temperature are investigated experimentally. For this purpose, the specimens are loaded uniaxially while the temperature is increased up to 800 °C. The obtained results provide the proper basis for the development of realistic material models, allowing more sophisticated simulations of structures exposed to fire.

Rate-dependent models require creep or mechanical tests at various strain rates in order to be identified and validated. Different geometries coexist for creep and static tests (normative geometry) and for dynamic tests. Therefore, due to geometrical sample considerations, experimental results could be inconsistent for identification or validation procedures, inducing, for example, differences on the shear modulus only due to the change of geometry.

The objective of this work is to present an improved sample geometry that allows to obtain consistent mechanical tests results at various strain rates highlighting the rate dependencies of laminates. In particular, a complete mechanical validation of the sample geometry for dynamic tests is successfully performed in order to avoid inconsistency. Results of static and dynamic tests on the validated geometry are analysed, and the rate dependency of the elastic properties of the UD T700GC/M21 mesoscopic ply is highlighted on a wide strain rate range (10⁻³ to 10² s⁻¹). Finally, the identification of a non-linear viscoelastic model is performed on dynamic and creep tests results in order to obtain a representative model for dynamic, static and creep loadings, and to demonstrate the importance of introducing the improved geometry for the dynamic tests.

The measurement of early shrinkage cracking in concrete is important to prevent aesthetic issues and avoid surface cracking that could lead to reinforcement corrosion and reduce the durability, long-term service life and integrity of a structure. Moreover, the lack of standards and subjectivity of the very few methodologies proposed so far complicate its estimation.

This research presents a new imaging methodology for evaluating and quantifying early shrinkage cracking patterns. The methodology was developed testing highly restrained square concrete slabs subjected to severe conditions of restraint and moisture loss. Its quantification consisted of photographing, processing the pictures and highlighting the cracks. For the first time, early shrinkage cracking in concrete can be measured through an experimental technique and quantified by means of geometric figures. In this way, more precise and automatic results are achieved, as flat figures adapt to the shape of cracks and store their properties. Therefore, parameters such as the total cracked area, total crack length, maximum crack width or average crack width were easily calculated.

The results demonstrated the suitability of the wind tunnel test to produce significant cracking patterns, as well as the great capacity of the imaging methodology to identify and characterize the cracking pattern.

A unique strain gauge based method is developed to identify the magnitude and location of a load on a slender beam with variable cross sections, and pinned, firm rest, soft rest, pinned-fixed, and fixed boundary conditions. Four uniaxial strain gauges are mounted to the bottom surface of the beam, and the bending moment diagram of the beam can be constructed using measured strains on the beam. By combining individually scaled strain gauge outputs, the magnitude and location of the load can be accurately identified. The strain gauge based force transducer methodology is experimentally validated on prismatic beams with firm rest, soft rest, firm rest-fixed, and fixed boundary conditions, and a continuously tapered beam with rest boundary conditions. The force transducer methodology is independent of the boundary conditions of the beam, and the error from strain gauge drift due to uniform thermal expansion on a prismatic beam can cancel out.