Narrow Results

We present a robust method to locate and continue period-doubling, saddle-node and symmetry-breaking bifurcations of periodically driven experimental systems. The method is illustrated from results obtained for an electronic implementation of a Duffing oscillator.

Nonlinear dynamic behavior of a cantilever cylindrical shell is studied experimentally using non-contact type of electromagnetic shaker, acceleration measurements, and imaging of vibrating shell using two high speed 3D cameras. The response history and frequency spectrum are measured at different locations along the circumference of the free end of the shell for different excitation amplitudes and mode of vibration. The frequency response obtained from acceleration measurements is found to be in good agreement with the simulated response in ANSYS. The response histories from acceleration data and digital image correlation are compared for one case and found to match very well. The traveling wave phenomenon along with participation of higher harmonics and softening nonlinearity are observed. The traveling wave response is observed for certain range of forcing frequency for the shell excited in modes with number of circumferential waves n = 3 and 5. It is shown that the traveling wave response can be detected based on the phase angle difference of response at different circumferential locations.

In this paper, we propose a new multicellular design of assembled multi-frusta with alternate orientations and varied taper angles for effective energy absorption applications. Extensive crush test experiments, comprehensive finite-element simulations and analytical modeling were carried out to evaluate the energy absorption performance of the newly proposed multicellular assemblies. The performances of these assemblies are calibrated against conventional assembly of uniform tubes. Two aspects of the work were parametrically examined. The first was concerned with the effect of the frusta taper angle, while the second was concerned with the multi-frusta layout on the energy absorption of the proposed multi-frusta assembled structures. The results reveal that the face centered square layout with an appropriately selected taper angle possesses the optimal high specific energy absorption, low peak force, and smooth crushing force curve, which makes it a crashworthy device.

Parametric analysis of hollow precast prestressed piles indicated that under certain conditions of loading and geometry, plastic hinge formation could be expected in the pile shaft below ground level. Four half-scale model precast prestressed piles were tested in flexure to characterize plastic hinge development. The test rig simulated the subgrade moment pattern found in an in situ pile, and simulated external confinement from the soil around the pile shaft. Parameters varied were transverse reinforcement ratio, presence of external confinement, and presence of nonprestressed longitudinal steel in the plastic hinge region. The model piles were found to be insensitive to parameter variation. Failure occurred at similar levels of structural displacement in all cases, and in all cases took the form of compression failure of the pile wall. The piles had limited ductility, less than μ_Δ = 4 in all cases.

An innovative and practical technique for the seismic rehabilitation of beam-column joints using fiber reinforced polymers (FRP) is presented. The procedure is to upgrade the shear capacity of the joint and thus allow the ductile flexural hinge to form in the beam. An experimental study is conducted in order to evaluate the performance of a full-scale reinforced concrete external beam-column joint from a moment resisting frame designed to earlier code then repaired using the proposed technique. The beam-column joint is tested under cyclic loading applied at the free end of the beam and axial column load. The suggested repair procedure was applied to the tested specimen. The composite laminate system proved to be effective in upgrading the shear capacity of the nonductile beam-column joint. Comparison between the behaviour of the specimen before and after the repair is presented. A design methodology for fibre jacketing to upgrade the shear capacity of existing beam-column joints in reinforced concrete moment resisting frames is proposed.

Non-ductile response of structural elements, particularly columns, has been the cause of numerous documented failures during earthquakes. The objective of this experimental study was to evaluate the non-linear behaviour of non-ductile reinforced concrete short columns under lateral cyclic deformations and to evaluate rehabilitation schemes. Three reinforced concrete short columns were tested under cyclic lateral loads and constant axial load. The behaviour and effectiveness of different rehabilitation systems using carbon fibre reinforced polymers (CFRP) were investigated. Two different techniques to improve concrete confinement were used in the two rehabilitated specimens. It was found that it is possible to eliminate the non-ductile modes of failure of short column using anchored CFRP wraps. In addition, an analytical model to predict the confining effect and the total shear resistance of rectangular reinforced concrete columns with anchored fibre wraps was introduced. The confinement model is an extension to an available model for concrete confined by steel reinforcement. The model was used to predict the shear capacity of the tested specimens and has shown good results.

An experimental program for identifying the causes of failures in structural walls under earthquake loading and investigating potential rehabilitation schemes was undertaken. Large-scale models of the plastic hinge region of the walls were tested. An innovative test setup that provides the possibility of controlling the ratio of the shear force to both bending moment and axial load was constructed. A control wall was tested and failed prematurely in shear reproducing the failure observed in the field. Two different rehabilitation schemes to improve the behaviour of the wall using biaxial fibre reinforced polymer (FRP) sheets were designed to prevent the shear failure. To improve the ductility, the end column elements of the walls were confined using anchored FRP. The two schemes were tested and proved to be effective in increasing shear strength, ductility, and energy dissipation capacity of the walls.

An experimental investigation was conducted to study the failure mode of existing reinforced concrete columns designed during the 1960s. The effectiveness of using corrugated steel jackets for enhancing the seismic flexural strength and ductility of these types of columns was examined. Three large-scale columns were tested under cyclic loading. The three columns represent existing column, current code-detailed column and rehabilitated column. The variables in the test specimens include the amount of column transverse reinforcement and jacketing of the column. The corrugated jacket was found to be effective in the rehabilitation of the selected existing structure, which does not meet the current seismic code requirements. A method is proposed for the design of the corrugated steel jacket to enhance the lap splice capacity and ductility of the column.

The use of shape memory alloys (SMAs) in engineering applications has increased the interest of the accuracy analysis of their thermomechanical description. This work presents an uncertainty analysis related to experimental tensile tests conducted with shape memory alloy wires. Experimental data are compared with numerical simulations obtained from a constitutive model with internal constraints employed to describe the thermomechanical behavior of SMAs. The idea is to evaluate if the numerical simulations are within the uncertainty range of the experimental data. Parametric analysis is also developed showing the most sensitive constitutive parameters that contribute to the uncertainty. This analysis provides the contribution of each parameter establishing the accuracy of the constitutive equations.

The use of two-phase ejector in improving the performance of transcritical CO₂ refrigeration system needs further experimental verification particularly the effects of its geometrical design. In this study, experimental data were gathered for ejectors with different mixing cross-sectional areas at different operating temperature and pressure. The results have shown that a smaller mixing area yields higher efficiency due to its higher pressure recovery and entrainment ratio, but its advantages are limited to lower ejector inlet pressure P_c. A larger mixing area is required for higher cooling capacity which can be achieved at higher ejector inlet pressure or lower ejector inlet temperature but excessive increase in this area considerably decreases the efficiency of the system. In this study, the ejector with the largest mixing area was the most inefficient and reduced the COP up to 10% compared to most efficient type. It demonstrates the significant effect of ejector's geometrical features, particularly the mixing cross-sectional area and its related geometrical ratio, in the performance of CO₂ ejector system. The effect of motive nozzle inlet condition on pressure recovery profile has been more evident for ejector with smaller mixing area while the evaporator temperature has the least effect in the performance of the system. In the conditions used in this study, using ejector yielded a COP improvement of up to 35% compared to the conventional system.

This work presents the experimental evaluation of the energy performance of transcritical CO₂ refrigeration and heat pump systems. The optimal gas cooler pressures and the optimal COP have been analyzed from a thermodynamic point of view. The systems used a new dual expansion valve and a balance CO₂ liquid receiver adjustment device, which can control high and low side pressure effectively. Moreover, we demonstrate the influence of the internal heat exchanger (IHX) on the systems' performances, on the basis of the analysis of the relative COP index RCOPI, the compressor power index RP_CI and other parameters which can confirm the truth of. The experimental evaluation covers five evaporating levels (-10 to 10°C) and in a wide range of gas cooler pressures (75 to 120 bar). It is concluded that with the IHX system, compressor power is relatively low when the high side pressure is over 100 bar, and the evaporation temperature is below 0°C. The COP of the system without the IHX is slightly higher than the system with the IHX; it is increasing about 3% to 5%, when the evaporation temperature is over 5°C. Relative to the single expansion process, the dual expansion cycle can decrease the influence of pressure fluctuations of CO₂ supercritical fluid and liquid mixture on the systems.

This paper provides the results of experimental stream flow patterns (water–oil) investigated in vertical and horizontal pipes with an elbow. The pipes are made from Perspex; the inner diameter is 0.024m, and the lengths of the vertical and horizontal pipes are 6 and 3m, respectively. The values of pressure at the four locations where $l/d=62$, 138, 248, and 304 are measured in various cases. The superficial velocities of the water range from 0.1 to 0.4m/s and of the oil from 0.1 to 0.9m/s. The pressure decreases with an increase in the height and the speed. Droplet/elongated/churn and annular streams are observed in a vertical pipe. The flow patterns are the stratified wavy stream with droplets at the interface, scattering (dispersion) of oil in water with a water layer, and annular flow in the horizontal pipe. These results of flow patterns are determined by a digital camera.

A three-finite element model to simulate the single point incremental forming (SPIF) of AA3003-H12 parts is developed. Tool motion in the simulation environment and the CNC milling machine is controlled using new protocols developed especially for SPIF process of pyramidal parts. Numerical measured part thickness and geometry are found to best agree with the experimental ones. Due to the lack of tools, enabling a proper selection of numerical factors to overcome computation convergence problems and product conformity error, trial and error method is applied alternately and proves to be effective. Thickness distribution, equivalent stress distribution, finite element size and friction coefficient effect on the final thickness distribution, geometric profile and computation time are studied. In order to understand the failure and fracture mechanisms in the produced part, the stress state, thickness and equivalent stress history at the thinned finite element are equally studied. Results show a critical thinning occurs at the part corners more dramatic than in the walls. Equivalent stress presents great values first at the part corners and second at the fillets. Failure areas do not coincide with fracture ones due to different deformation mechanics. The increase of the finite element size increases the thickness and the geometry error, but reduces significantly the computation time. The friction coefficient does not significantly affect the thickness and geometry, leading to a significant computation time reduction.

The quantity notions in mathematics and metrology and their relation and interaction are considered. The quantity in mathematics belong to the modelling field and is an ideal object while the quantity in metrology has an experimental character and so is an uncertain object. Every metrological model object including measurement aim, measurand, metrological characteristic of a measuring instrument, are expressed by mathematical quantities. When the model object is evaluated by using measurement, so the experimental quantity is obtained, that is metrological quantity. Because of the principal uncertain character of metrological quantities, measuring data and relating metrological quantities have to be processed using firstly non-classic mathematical means but of special type, taking into account the above-mentioned character. There are approximate linear equations theory, interval arithmetic, fuzzy set, and so on. There is not wide use of these means. The reasons are traditions, and absence of data structure analysis, and special place of stochastic tools. The latter is conditioned by some peculiarities of probabilistic-stochastic models. Main, and wide spread, mistakes or faults in use of these models are discussed. Indirect measurement is considered as the field of most complicated interaction of experimental and mathematical quantities.

To investigate the mechanical behaviour of laminated glass with the elasto-viscoplastic ionomer interlayer SentryGlas® by DuPont, an experimental program was executed on full-scale glass laminates. The results of this research improved the insight in the complex mechanical behaviour of this stiff interlayer. More specifically, a clear influence of load duration and temperature could be observed for both creep and relaxation during torsion experiments. Namely, within the tested temperature range of 5 °C up to 65 °C, torsional stiffness changed with a factor 3.

To investigate the mechanical behaviour of laminated glass with the elasto-viscoplastic ionomer interlayer SentryGlas® by DuPont, an experimental program was executed on full-scale glass laminates. The results of this research improved the insight in the complex mechanical behaviour of this stiff interlayer. More specifically, a clear influence of load duration and temperature could be observed for both creep and relaxation setups during bending experiments. The stiffness reduction due to the load duration and the temperature raise was most significant for the smaller specimens — with a span of 1m — while for the largest specimen — with a span of almost 3 meter — the reduction remained less than 25% of the monolithic bending stiffness, even after a load duration of 48 hours at 65°C.

The assessment of the post-breakage performances of laminated safety glass elements used in construction needs to take into account the sensitivity to the temperature of the mechanical behaviour and properties of the product, in particular of the interlayer material. After a general problem statement, an overview is given of tests at different scales, with typical observations and results for two different interlayer materials. Through the different presented experimental scales, the mechanisms ruling the bridging behaviour in cracked laminated safety glass are explained, highlighting the difficulty of assessing the mechanical properties to be used in practical design calculations.