Dynamic behaviour of Reinforced Concrete (RC) structures can be assessed using a Single-Degree-of-Freedom (SDOF) approach. Such a method is highly dependent on the resistance curve of the structure which is generally represented by a bilinear elasto-perfectly-plastic approximation. This approximation might lead to erroneous results when it refers to the use of externally bonded Fibre Reinforced composites for flexural capacity upgrade of Reinforced Concrete (RC), mainly when the concrete-to-FRP interface failure is to be included. One-way slabs are experimentally and numerically investigated in this study in a 3-point flexural configuration. Assessment on the load-displacement behaviour of a reference specimen and its retrofitted counterpart is performed. Special attention is given to the behaviour of the structure after the concrete-to-FRP failure. Comparison is made between experimental, numerical and analytical results and a good agreement is obtained. A complementary analytical study based on the SDOF method is conducted to understand the influence of several resistance curves on the overall displacement of the same structure when subjected to different pressure-impulse combinations.

In this paper the design and recalculation of new type ceiling elements made of carbon reinforced concrete (CRC) is described. With the use of the high-potential composite material carbon reinforced concrete, structures can be, compared to conventional steel reinforced concrete (RC), designed and manufactured slimmer and lighter. Because of this and the increased sustainability of ceiling elements made of CRC a noteworthy amount of concrete can be saved. To show the potential of CRC elements, four different structures for various fields of application are shown. The first ceiling element, which will be introduced, fits perfectly for the use in multi-storey car parks because of the high resistance of the carbon fibers against corrosion. Another CRC structure in this paper was created in a research project as a demonstrator to show the potential of the newly developed concrete mixture for CRC. To prove the ability of this new developed concrete, large-scale CRC I-beams were produced in a precast concrete factory. The third ceiling element was designed and manufactured in form of a shell to combine the high strength composite material with an improved design for ceiling elements. The last introduced CRC element was developed as demonstrator in another research project and was designed in form of a ribbed slab.

With the non-periodicity and discrete nature, and unnecessary of phase unwrapping process, digital speckle correlation method shows its significant advantages in three-dimensional (3D) shape measurement. Combining with the spatial correlation and temporal correlation method in the digital speckle correlation, a spatio-temporal digital speckle correlation was developed in this paper, which can improve the accuracy of 3D shape measurement and effectively reduce the number of the recorded speckle images for restoring the corresponding 3D shape at the same time. In the experiment, only 5 frames of the required speckle images was needed to reconstruct the 3D shape of a complex object with spatio-temporal digital speckle correlation method, and its accuracy was same as the result when 20 frames speckle images were used in temporal correlation method.

This contribution shortly introduces the anisotropic, micromechanical damage model for sheet molding compound (SMC) composites presented in the authors’ previous publication [1]. As the considered material is a thermoset matrix reinforced with long (≈ 25mm) glass fibers, the leading damage mechanisms are matrix micro-cracking and fiber-matrix interface debonding. Those mechanisms are modeled on the microscale and within a Mori-Tanaka homogenization framework. The model can account for arbitrary fiber orientation distributions. Matrix damage is considered as an isotropic stiffness degradation. Interface debonding is modeled via a Weibull interface strength distribution and the inhomogeneous stress distribution on the lateral fiber surface. Hereby, three independent parameters are introduced, that describe the interface strength and damage behavior, respectively. Due to the high non-linearity of the model, the influence of these parameters is not entirely clear. Therefore, the focus of this contribution lies on the variation and discussion of the above mentioned interface parameters.

The aim of this paper is to assess and compare the performance of both high speed 2D and 3D DIC configurations in the characterization of unidirectional carbon fiber reinforced epoxy composites in high strain rate tension in the transverse direction. The criteria for assessment were in terms of strain resolution and measuring the strain localization within the gauge section. Results showed that the high speed 3D DIC technique has lower strain resolution compared to the high speed 2D DIC technique. In addition, the analysis of the full strain fields indicated that the 3D DIC technique could accurately locate and measure the concentrations of strains within the gauge section of the tested samples.

The attenuation of stress wave and energy absorption in the coral sand were respectively investigated in this study. A series of experiments were carried out by using a new methodology with an improved split Hopkinson pressure bar (SHPB). Four kinds of coral sand, i.e., particle sizes of 1.18-0.60mm, 0.60-0.30mm, 0.30-0.15mm, and 0.15-0.075mm, are carefully sieved and tested. Significant effects of coral sand on attenuation of stress wave and energy absorption are observed, where, the correlation between the stress wave attenuation and energy absorption of coral sand is also validated. A similar conclusion was drawn on stress wave attenuation and energy absorption from the test results. There exists a common critical stress zone for the sieved coral sands, when the stress below this zone, sand with small particle size attenuates more stress wave and absorb greater energy; when the stress beyond this zone, sand with greater particle size behaves better on stress wave attenuation and energy absorption.

An innovative mechanical testing method (Compressive Circular Ring Method) is provided for measuring Young’s modulus of each layer in a flexible multi-layered material. The method is based on a nonlinear large deformation theory. By just measuring the vertical displacement or the horizontal displacement of the ring, Young’s modulus of each layer can be easily obtained for various thin multi-layered materials. Measurements were carried out on an electrodeposited two-layered wire. The results confirm that the new method is suitable for flexible multi-layered thin wires. In the meantime, the new method can be applied widely to measure Young’s modulus of thin layers formed by PVD, CVD, Coating, Paint, Cladding, Lamination, and others.

In this paper, a wind tunnel experiment model for elastic aircraft with high-aspect-ratio is designed. The numerical simulation method is used to predict the state of the wind tunnel experiment, and the low-speed wind tunnel experiment is carried out. The purpose of this study is to verify the effect of geometric nonlinearity on the aerodynamic force of aircraft with high-aspect-ratio, and to obtain the aeroelastic trim parameters and influence of elastic deformation on aerodynamic forces. Some parts of the model are fabricated by 3-D print using nylon to reduce weight. The aircraft aeroelastic deformation is measured using the principle of binocular vision measurement, aerodynamic is measured using balance and angle of attack is measured using attack angle sensor. the elastic deformation is simulated coupled CFD method and finite state induced inflow aerodynamic model with geometrical exact intrinsic beam model which can accurately describe the geometrical nonlinear effect of high-aspect-ratio wing. By comparing the experimental data and numerical simulation results, the the influence of geometric nonlinear effect on aerodynamic force is quantitatively evaluated. Research show that the wind tunnel experiment device and supporting measurement device built for high aspect ratio aircraft can effectively acquire the influence of geometric nonlinearity on aircraft aerodynamic force.

The topic of this paper is an improved PolyMAX for a system with close modes or heavy damping. Due to the phenomenon of modal interference induced by close modes or heavy damping, the effectiveness of system identification may be therefore degraded. According to the theory of mechanical vibration, the response data function can be expressed in rational fraction form through the curve fitting technique, and the modal identification can be implemented from parametric estimation from rational fractional coefficients. However, we cannot acquire the mode shape information because the conventional common denominator model only indicates the frequency response function of a single-degree-of-freedom system. In this paper, we propose the matrix-fractional coefficients model constructed by the frequency response functions of a multiple-degree-of-freedom system to perform modal estimation. In addition, to get rid of the phenomenon of omitted modes from the distortion from modal interference among the vibration modes of a system, we introduce a system model with higher-order matrix-fractional coefficients in the proposed method. The vibration modes of systems and fictitious modes caused by the numerical computation can be effectively separated through the different-order constructed stabilization diagram. Modal identification can be implemented by solving the eigenproblem of companion matrix yielded from least square estimation. Numerical simulation of a full model of sedan, confirms the validity and robustness of the proposed parametric-estimation method for a system with modal interference.

Two-phase bubbly flow is a fundamental phenomenon which occurs in many industrial processes such as thermal power plant, chemical processes, nuclear reactors, and so on. It has been investigated continuously over several decades. However, due to its complexity, some characteristics of the phenomenon have not yet been understood. The velocity profile of liquid and bubble is an important parameter in the bubbly flow. Also, it is used to calculate other parameters such as void fraction and slip velocity. Hence, measurement of the velocity profile in bubbly flow is required.
The Ultrasonic Velocity Profile (UVP) method [1] is a nonintrusive measurement, which can measure velocity profile of the fluid even though is opaque. The method does not require the transparent test section. The UVP measurement uses a pulsed echography of an ultrasonic wave reflected from moving reflector which has a similarity of velocity with a fluid such as a particle dispersed in a fluid. It contains Doppler signal. The frequency of Doppler signal fD (x) directly relates to a velocity of moving particle. Therefore, the instantaneous velocity profile of the fluid along its measurement line can be obtained by observing Doppler frequency. Although conventional UVP can obtain velocity profile of liquid and bubble, the velocity of both phase cannot be classified separately.
This study proposes a measurement technique to obtain velocity profile of liquid and bubble in two-phase bubbly flow using UVP method. The previous study by Murakawa [2], two resonant frequencies was used to measure both liquid and bubble velocity separately. The system requires more devices However, present study employs only single resonant frequency. Therefore, a measuring equipment is minimized. To measure and separate velocity distribution of liquid and bubble with single resonant frequency, a technique of measurement and separating velocity of both phases are developed. In bubbly flow, Doppler signal is demodulated from echo signals reflected by particle (liquid) and bubble. Its frequency and amplitude inform the velocity and the identity of each reflector respectively. In some case, the position of particle and bubble occurs in same measurement channels. When this behavior occurs, multi-frequency and different amplitude in Doppler signal are generated. Therefore, advanced signal processing is required to analyze the effect of Doppler signal for decomposing Doppler frequency of particle and bubble. Then, the phase separated velocity of liquid and bubble can be obtained.
For confirming the applicability of modified measurement system, the developed UVP was used to experiment on vertical pipe flow apparatus. The measurement accuracy of developed UVP was guaranteed due to the result had good agreement with UVP Original and PIV method. Furthermore, the UVP was applicable to observe velocity distribution of both phases in a bubble column.
References
[1] Y. Takeda, Velocity profile measurement by ultrasonic Doppler shift method, Int. J. Heat Fluid Flow, 7, (1986), pp.313-318.
[2] H. Murakawa, H. Kikura, and M. Aritomi: Application of ultrasonic Doppler method for bubbly flow measurement using two ultrasonic frequencies, Experimental Thermal and Fluid Science, 29, (2005), 843-850.