Abstract in English:Abstract Structural adhesives are increasingly being used in the aerospace and automotive industries. They allow for light weight vehicles, fuel savings and reduced emissions. However, the environmental degradation of adhesive joints is a major setback in its wide implementation. Moisture degradation of adhesive joints includes plasticization, attacking of the interface, swelling of the adhesive and consequent creation of residual stresses. This may lead to reversible and irreversible damage. In this work double cantilever beam (DCB) specimens using two different adhesives for the automotive industry were subjected to two different ageing environments. They were tested periodically until the toughness of the adhesives stabilized, which means that they were fully degraded. An association was made between the toughness of the adhesive and the amount of water that it had absorbed. This way it was possible to indirectly measure the water uptake in an adhesive joint taking into account the water uptake properties of the adhesives studied, which had been determined in another study. It was found that diffusion of water into the studied adhesive joints was faster than diffusion through the bulk adhesive alone. A model that takes into account diffusion through the interface between the adhesive and the adherends was proposed.
Abstract in English:Abstract This paper presents the effect of sequence loading on fatigue crack growth of API X65 steel tested in room temperature. Most of pipeline steels are subjected to wide spectrum of loading during the length of service. Influence of load history effect can cause a trickier assessment to the fatigue behaviour. The objective of this study is to determine the fatigue crack growth behaviour under sequence loading. The material used in this study is X65 steel grade, broadly used in transporting the oil and gas. The constant amplitude loading under mode-I loading and stress ratio of 0.1 and 0.7 are investigate. The effects of sequence load are presents by the two-level block loading. The retardation effect is more intense for block sequence loading. At least about 9.7x104 delayed numbers of cycles was observed which is two times longer compared to constant amplitude loading. The load sequence was suggested affected by retardation consequently delayed the crack growth. It was further observed an increase of overload load ratio consequently resulted a crack grows faster about 18%. It was concluded a lengthy in crack growth was associated with the delay cycles suggesting that the fatigue life depends mainly on size of delay zone and compressive residual stress near the crack tip.
Abstract in English:Abstract This article presents the results of numerical investigation on modeling buckling behavior and ultimate strength of corroded multi-planar tubular joints. Finite element method was used in order to simulate the behavior of DX multi-planar tubular joints under axial compressive loading. Three different patterns were chosen for corrosion modeling. Also the effects of corrosion-related parameters such as age and depth of corrosion were evaluated. The first corrosion pattern is based on uniform reduction of wall thickness over a portion of tube length while the second pattern represents a sinusoidal reduction of thickness. The third pattern of corrosion uses average thickness and standard deviation as main parameters for defining a random corroded region. A linear criterion for predicting corrosion wastage has been used for the first and the second patterns, whereas predictions of the third pattern are determined by a nonlinear method. The results indicate differences in the ultimate strength concluded from different patterns. It was found that conventional methods are conservative in evaluating the strength of corroded tubular joints of jacket platforms. Amongst 3 methods used for modeling corrosion, the third and the second pattern had similar results. It was also shown that corrosion is ineffective in braces and increasing the number of waves for the second pattern will result in increase of joint strength. The optimum sizes of elements were defined by implementing an analysis of model sensitivity toward element size.
Abstract in English:Abstract This paper investigates the mechanical properties and corrosion behavior of Metal Matrix Composites prepared using Al7075 alloy as a matrix, Silicon Carbide and Titanium Carbide as reinforcement particles. Two step stir casting process was used to fabricate the composites by varying volume fractions of Silicon Carbide and Titanium Carbide (0 to 15 vol. %). Microstructural analysis, mechanical and corrosion behavior were used to evaluate the performance of the composites. Uniform distribution of reinforcement particle was observed through optical photomicrographs. Vickers micro hardness tests were performed and the hardness values were increased with an increase in reinforcement from 0 to 15 vol. %. The tensile strength of the 10 vol. % of aluminum hybrid matrix composite was better than that of the base alloy. In 3.5% NaCl solution, it was observed that the 15 vol. % of the aluminum hybrid matrix composite have higher corrosion resistance in comparison the base alloy.
Abstract in English:Abstract In this paper, distribution of peeling stress in two types of adhesively-bonded joints is investigated. The joints are a single strap and a stiffened joint. Theses joints are under uniform tensile load and materials are assumed orthotropic. Layers can be identical or different in mechanical or geometrical properties. A two-dimensional elasticity theory that includes the complete stress-strain and the complete strain-displacement relations for adhesive and adherends is used in this analysis. The displacement is assumed to be linear in the adhesive layer. A set of differential equations was derived and solved by using appropriate boundary conditions. Results revealed that the peak peeling stress developed within the adhesive layer is a function of geometrical and mechanical properties. FEM solution is used as the second method to verify the analytical results. A good agreement is observed between analytical and FEM solutions.
Abstract in English:Abstract Parametric study of composite-steel double lap joint under tensile loading is performed using finite element modeling. The joint is such that steel is placed between a straight and a curved composite sublaminate. Three joint characteristics including maximum Von Mises stress in adhesive layer, stiffness and weight are investigated. Design curves are provided to study the influence of geometric parameters on the joint behavior to determine the joint performance. The curves illustrate sensitivity of three mentioned joint characteristics to geometric variations. Selected parameters are adhesive thickness, overlap length, composite sublaminates’ thickness and stiffness ratio. Results indicate variation of parameters may have either significant or negligible influence in the performance of the joint. Results also show that variation in geometric parameters does not make monotonous change in the performance of the joint and in some cases rate of the changes may differ. From the prepared curves it can be understood that increase in overlap length and adhesive thickness will decrease maximum Von Mises stress in adhesive layer and global stiffness of the joint. In case of sublaminate thickness decrease in the thickness of straight sublaminate leads to decrease in maximum stress in adhesive layer while the stiffness is increased. For the stiffness ratio an optimized point can be found beyond which maximum stress will increase. Global stiffness of the joint increases by increase in stiffness ratio. Changes in weight of the joints are easily calculated from the geometry and are reported in the text.
Abstract in English:Abstract State-of-the art studies of impact crushing circular stepped tube (inversion tube) introduce various approaches to improve the energy absorption capacities. Adding external longitudinal stiffeners on the circular stepped tubes is a new approach that have a great effect and interest. In the current study, finite element analysis using (LS-DYNA/WORKBENCH ANSYS) is performed on a series of numerical models of aluminum circular stepped tubes that are externally stiffened by a constant number of longitudinal stiffeners distributed around the cross section of the circular stepped tube. The numerical models are implemented under an axial impact crushing scenario. Furthermore, a new improved formula for prediction of steady inversion load is proposed. The theoretical predictions are found to be in good agreement with the numerical results with an error within 12%. A comparative study is conducted to compare the energy absorption characteristics and inversion mechanism between the newly proposed tubes and the conventional stepped tube. The results showed that addition of external longitudinal stiffeners on circular stepped tubes could imply greatest improvement for the energy absorption up to 104%, specific energy absorption capability (energy absorption per unit mass) up to 54.9%, the crush force efficiency up to 40.3% and increase the inversion stroke length in comparison with the unstiffened circular stepped tubes. A newfound role of external longitudinal stiffeners added to the stepped tubes that controls the inversion and deformation mechanism is presented.
Abstract in English:Abstract The classical problem of the response characteristics of uniform structural member resting on elastic subgrade and subjected to uniform partially distributed load is studied in this work. The closed form solutions of the governing fourth order partial differential equations with variable coefficients are presented using an elegant analytical technique for the moving force and mass models. Various results and analyses are carried out on each of the pertinent boundary conditions and phenomenon of resonance is studied for the dynamical system. It was found that in all illustrative examples considered, for the same natural frequency, the critical speed for moving distributed mass problem is smaller than that of the moving distributed force problem. Hence, resonance is reached earlier in moving mass beam-load interaction problem. Finally, this work has suggested valuable methods of analytical solution for this category of problems for all boundary conditions of practical interest.
Abstract in English:Abstract Composite structural elements of steel-concrete began to be used only in 1960 after the development of methods and constructive dispositions that ensured the functionality of these two materials together. In order to verify the importance of the participation of the axial mode in the frequency spectrum of the free vibration problem in composite beams with deformable shear connection, several analyses for 4 different boundary conditions and stiffness connection variation were performed. The analysis of the problem was carried out by development and computational implementation of a finite element for composite beams with partial interaction in the longitudinal direction applied to the problem of free vibrations. The solutions to this problem in the literature are scarce, and project recommendations are simplified. The results show that the finite element exhibits an excellent performance compared with the analytical results and as the axial mode has a high modal contribution, despite the boundary condition and stiffness connection.
Abstract in English:Abstract The present study is based on experimental investigation and numerical simulation of impact of different nose shape projectiles on thin polycarbonate plates. Rigid hardened projectiles of two different geometries (Blunt and Truncated cone) keeping the same shank diameter and total mass were prepared. These projectiles were impacted through pneumatic gun setup on circular polycarbonate plates at varying impact velocities upto 106 m/s. Impact and residual velocities were measured before and after perforation, respectively. Numerical simulations were performed in ABAQUS/EXPLICIT finite element code. The problem has been modelled based on Mie-Gruneisen equation of state. The experimental results obtained in terms of ballistic limit, residual velocity, energy absorbed and deformation mechanism have been compared with the numerical results and are found to be in excellent agreement. It is observed that the ballistic limit for normal impact is greater for blunt projectile compared to truncated conical projectile. Velocity drop and the energy absorbed is higher for blunt projectile compared to truncated conical projectiles for the impact velocities under study.