Numerical Simulation of Dynamic Characteristics of Dam Concrete Based on Fuzzy Set

The dynamic characteristics of concrete are the key point of the dam seismic safety design. In order to study the dynamic characteristics of concrete, a CT scan test of concrete under dynamic load was carried out; CT scan images of the concrete loading process were obtained. Based on the definition of integrity, integrity area, and intercepted sections in the quantitative zoning theory, the concrete CT images were divided into the hole or crack area ( P 0 − λ 1 ), hardened cement stone area ( P λ 1 − λ 2 ), and aggregate area ( P λ 2 − 1 ). And the determination method of partition threshold is studied. Then, based on the CT resolution unit, a concrete numerical calculation model of structural random is established, and the numerical simulation experiment of concrete under uniaxial dynamic load is carried out. The results show that the concrete numerical calculation model of structural random is very close to the actual mesostructure of concrete, and the interface thickness between aggregate and hardened cement is very close to the actual interface thickness (which is 40~50 μm). Under the action of dynamic load, the damage of the sample is mainly concentrated in the upper part of the sample, and the damage is easy to occur at the initial defect place, and the damage occurs at multiple points at the same time. The damage crack is relatively straight, the phenomenon of the crack passing through the aggregate is obvious, and the crack expands along the fastest path of energy release.

Process Variable Optimization of Cold Metal Transfer Technique in Cladding of Stellite-6 on AISI 316 L Alloy Using Grey Relational Analysis (GRA)

In this work, an attempt was made to identify the optimised parameter combination in cold metal transfer (CMT) cladding process of AISI 316 L austenitic stainless steel. cladding process was carried out using stellite 6 filler wire. Experiments were carried out based on L31 central composite design (CCD). Cladding was done with current, Voltage, torch angle and travel speed as input parameters. Quality of the clad was analysed by measuring depth of penetration, weld area, hardness of the clad surface, corrosion rate and clad interface thickness. Grey relation analysis was used to identify the optimised parameter combination. Trial number 18 was identified as the optimised parameter combination. The optimised input parameters are Welding Current 200 Amps, Voltage 19 V, Torch Angle 70⁰ and Welding Speed 150 m/min. ANOVA was used to identify the most influencing parameters on the overall multi-objective function and it was understood that the combined effect of torch angle, travel speed had a significant influence on the clad quality. Further investigation was carried out through an optimised set of parameters. The cladding experiment was conducted and their surface was investigated through clad profile, hardness of the cladded area, interface thickness of cladding region and corrosion rate.

Influence of Manufacturing Process in Structural Health Monitoring and Mechanical Behaviour of CNT Reinforced CFRP and Ti6Al4V Multi-Material Joints

Co-cured multi-material metal–polymer composites joints are recent interesting structural materials for locally reinforcing a structure in specific areas of high structural requirements, in fibre metal laminates and lightweight high-performance structures. The influence of manufacturing processes on the morphological quality and their mechanical behaviour has been analysed on joints constituted by sol-gel treated Ti6Al4V and carbon fibre reinforced composites (CFRP). In addition, carbon nanotubes (CNT) have been added to an epoxy matrix to develop multiscale CNT reinforced CFRP, increasing their electrical conductivity and allowing their structural health monitoring (SHM). Mechanical behaviour of manufactured multi-material joints is analysed by the measurement of lap shear strength (LSS) and Mode I adhesive fracture energy (GIC) using double cantilever beam specimens (DCB). It has been proven that the addition of MWCNT improves the conductivity of the multi-material joints, even including surface treatment with sol-gel, allowing structural health monitoring (SHM). Moreover, it has been proven that the manufacturing process affects the polymer interface thickness and the porosity, which strongly influence the mechanical and SHM behaviour. On the one hand, the increase in the adhesive layer thickness leads to a great improvement in mode I fracture energy. On the other hand, a lower interface thickness enhances the SHM sensibility due to the proximity between MWCNT and layers of conductive substrates, carbon woven and titanium alloy.

A molecular dynamics investigation on fuel vaporization and mixing characteristics under sub/supercritical conditions

Molecular dynamics simulation is performed to study the influence of environmental pressure on the mixing process. Based on the OPLS-AA full-atomic potential function, the "gas-liquid-gas" simulation box model is used to study the evaporation characteristics of n-heptane at different environmental conditions. The results show that compared with the subcritical environment, the nitrogen molecules in the supercritical condition can diffuse into the liquid phase region earlier, and the temperature of the liquid phase rise faster, and then a unified supercritical fluid could be formed. Based on the density profile, a ?gas-liquid-gas? interface thickness is defined and the interface thickness is widened as the ambient pressure increase, resulting in the conventional subcritical evaporation transition to turbulent mixing process.

Modelling and Experimental Investigation of Hexagonal Nacre-Like Structure Stiffness

A highly ordered, hexagonal, nacre-like composite stiffness is investigated using experiments, simulations, and analytical models. Polystyrene and polyurethane are selected as materials for the manufactured specimens using laser cutting and hand lamination. A simulation geometry is made by digital microscope measurements of the specimens, and a simulation is conducted using material data based on component material characterization. Available analytical models are compared to the experimental results, and a more accurate model is derived specifically for highly ordered hexagonal tablets with relatively large in-plane gaps. The influence of hexagonal width, cut width, and interface thickness are analyzed using the hexagonal nacre-like composite stiffness model. The proposed analytical model converges within 1% with the simulation and experimental results.