A modified bond-based peridynamics model without limitations on elastic properties

This study proposes a novel Modified Bond-Based PeriDynamic (MBB-PD) model based on the bonds' classification. This classification of bonds is performed on the basis of the equivalent hypothetical local strains and falls into three categories of horizontal normal, vertical normal, and shear bonds. While the classical Bond-Based PD (BB-PD) considers only the stretch of bonds, all components of the bonds' strains are taken into account in the proposed model.A local imaginary element is considered around each bond to estimate the true strains of each bond. The constitutive relations are derived from equating the strain energies of the bonds' deformations to the Classical Continuum Mechanics (CCM) strain energies for a generalized combined loading condition. A novel critical stretch criterion and critical angle criterion are proposed to predict the failure of normal and shear strain bonds, respectively.It is also shown that, unlike the classical BB-PD, the proposed model does not impose any limitations on the value of Poisson's ratio. The model is verified by investigating some intact plane stress and plane strain problems under mechanical and thermal loadings. Moreover, the deformation and damage contours and the corresponding stress-strain responses are presented for different problems with pre-existing defects and validated with the eXtended Finite Element method's (XFEM) analysis

Critique and Analysis of Moniru Ravanipour’s Ecological Story “Ahle Ghargh” with a Look at the Discourse of Power

Ecological critique is the study of the relationship between literature and the natural world, the origins of which are the emergence of new ideas in anthropology and environmental issues that humanist discourses play an important role in their emergence. In the story of Moniru Ravanipour’s Ahle Ghargh, the relationships of the characters such as Kheyjo, Zayer Ahmad Hakim, Mah Jamal, Madine, and Mobor men with the environment are examined in this article to show how power relations at different levels of this story are effective based on Foucault's ideas. In this story, Kheyjo, Mah Jamal, Madine, and Zayer Ahmad Hakim have a close relationship with nature as well as a transcendental view of the earth that challenges the dominant discourse of the age, philosophical humanism; the humanism in which more attention is paid to human thought and looks at man and nature through the eyes of an element or object. This is why Foucault in the age of modernity sees the presence of man in the scene of the illustration of thought and consciousness, and argues that empirical combinations should be applied in a place other than the absolute rule of "I think". In this article, considering the importance and impact of discourses in the production of the literary text, the aim was to examine the story in question with a descriptive-analytical method of the human relationship with the environment and the impact of different discourses that play an effective role in exercising power to inform man about his behavior with the environment and to reveal his relationship with nature

Synthesis and Mechanical Properties Investigation of Nano TiO2/Glass/Epoxy Hybrid Nanocomposite

Mechanical properties of epoxy and glass/epoxy filled with 0.25, 0.5 and 1 vol% of TiO2 nanoparticles have been studied using tensile and three-point bending tests. For the TiO2/epoxy nanocomposites, the results showed that the strength and stiffness were improved, though the strain at ultimate strength point and breaking strain decreased. Moreover, the hybrid nanocomposites composed of 4 layers of woven E-glass fabric and TiO2/epoxy matrix were fabricated and cut onaxis and 45° off-axis by water jet. The results of tensile and three-point bending tests indicated a remarkable improvement in the strength and stiffness that could not be related to the mechanical improvement of the matrix. The samples containing 1 vol% nano TiO2 were improved relative to samples without the nanoparticles. The tensile strength of the on-axis and off-axis samples containing 1 vol% TiO2 increased by about 25.9% and 17.9%, in the order given, compared to that of the glass/epoxy specimens. In three-point bending test, the strength of the on-axis and off-axis specimens was improved 26% and 23.2%, respectively. In addition, the tensile stiffness of the onaxis and off-axis samples containing 1 vol% TiO2 increased, respectively, by about 14.4% and 17.5% compared to that of the glass/epoxy specimens. Also for the same on-axis and off-axis samples the three-point bending stiffness increased about 19.8% and 14.6%, respectively. The whole investigation on the microstructure of the hybrid nanocomposites illustrated that stronger interfaces between the fiber and TiO2/epoxy matrix were formed and improvement was noticed on mechanical properties of ternary composite compared to those of the fiber/epoxy composites. The analysis of damage zones of hybrid nanocomposites showed that the surface area of the damaged zone declined considerably due to the brittle behavior of TiO2-filled specimens but the area below the stress-strain curve, showing energy absorption during the test, increased

The effect of crack nucleation and growth on the mechanical properties in nanoindentation test

International audienceNanoindentation testing, also referred to as instrumented indentation testing, is widely used for the mechanical characterization of small volumes of materials. Since the application of coatings in industry has lately increased, accurate determination of the mechanical properties of coatings becameone of the most important concerns for scientists. Complete understanding of the mechanisms of crack initiation and growthseems necessary to determine the sources of error during nanoindentation test. There are few publications in the literature on the mechanisms of interfacial crack growth in the presence of pre-existing defect. Existence of pre-existing defect along the interface between the coating and the substrate leads to sooner initiation of the interfacial crack. One of the important issues that were not mentioned in previous worksis the position of the pre-existing defect and its effect on the failure mechanisms and mechanical properties. In this study we consider elastic-plastic coating on elastic-plastic substrate system and the cohesive zone model embedded in the finite element code is used to simulate the interface between coating and its substrate. The aim of this paper is to investigate the effect of interfacial crack growth in the presence of a defecton deformation behavior and some mechanical properties such as hardness and modulus of elasticity in Cu/Si coating system. Thereason that we choose Cu/Si interface is that experimental results show that the interface between Cu and Si layers in Si/Cu/SiN/Pt/C multilayer coating stuck is the most probable interface to delaminate during the test

Three dimensional Free Vibration and Transient Analysis of Two Directional Functionally Graded Thick Cylindrical Panels Under Impact Loading

AbstractIn this paper three dimensional free vibration and transient response of a cylindrical panel made of two directional functionally graded materials (2D-FGMs) based on three dimensional equations of elasticity and subjected to internal impact loading is considered. Material properties vary through both radial and axial directions continuously. The 3D graded finite element method (GFEM) based on Rayleigh-Ritz energy formulation and Newmark direct integration method has been applied to solve the equations in space and time domains. The fundamental normalized natural frequency, time history of displacements and stresses in three directions and velocity of radial stress wave propagation for various values of span angel of cylindrical panel and different power law exponents have been investigated. The present results show that using 2D-FGMs leads to a more flexible design than conventional 1D-FGMs. The GFEM solution have been compared with the results of an FG thick hollow cylinder and an FG curved panel, where a good agreement between them is observed

Dynamic and static analysis of FGM skew plates with 3D elasticity based graded finite element modeling

The present article deals with static and dynamic behavior of functionally graded skew plates based on the three-dimensional theory of elasticity. On the basis of the principle of minimum potential energy and the Rayleigh Ritz method, the equations of motion are derived in conjunction with the graded finite element approach. Solution of the resulted system of equations in time domain is carried out via Newmark's time integration method. Calculations are applied for fully clamped boundary condition. In the present paper, two different sets of distributions for material properties are considered. For the static analysis, material properties are considered to vary through the thickness direction according to an exponential law. In the case of dynamic analysis, variations of the volume fractions through the thickness are assumed to obey a power law function. Thus, the effective material properties at each point are determined by the Mori-Tanaka scheme. In case of dynamic analysis, the results are obtained for uniform step loadings. The effects of material gradient index and skew angle on displacement components and stress response are studied. Results of present formulations are verified by available results of a functionally graded rectangular plate for different boundary conditions and also compared with result of a homogenous skew plate by commercial FEM software

Investigation of Circular Woven Composite Preforms for Composite Pipes

The main traditional technique for commercial manufacturing of composite pipes is filament winding in which the winding angle and the discontinuity of the structure (caused by starting and ending points of the winding process) are two important matters of concern. In the present study, circular woven fabric with its orthogonal net-shaped continuous structure was produced from polyester yarns. Fabric was wet with epoxy and hand lay-up was used to manufacture the composite pipes. Composite pipes were subjected to internal hydrostatic pressure and their burst strength was recorded. In addition, tensile strength of flat laminas was assessed in the warp and weft directions. We estimated and analysed the failure strength of composite pipes using Tresca’s failure criterion and Finite Element (FE) modeling. The experimental burst strength was almost 23% more than the FE model and 77% more than the theoretical estimate