Computation of SIFs for cracked FGMs under mechanical and thermal loadings

The objective of this study is to present a numerical modeling of mixed-mode fracture in isotropic functionally graded materials (FGMs), under mechanical and thermal loading conditions. In this paper, a modified displacement extrapolation technique DET was proposed to calculate the stress intensity factor (SIFs) for isotropic FGMs. Using the Ansys Parametric Design Language, the continuous variations of the material properties are incorporated by specified parameters at the centroid of each element. Four numerical examples are presented to evaluate the accuracy of SIFs calculated by the proposed method. Comparisons have been made between the SIFs predicted by the DET and the available reference solutions in the current literature. A good agreement is obtained between the results of the DET and the reference solutions.

The main objective of this work is to present a numerical modeling of mixed-mode fracture in isotropic functionally graded materials (FGMs), under mechanical and thermal loading conditions. In this paper, the displacement-based method, termed the generalized displacement correlation (GDC) method, is investigated for estimating stress intensity factor (SIF). Using the ANSYS Parametric Design Language (APDL), the continuous variations of the material properties are incorporated by specified parameters at the centroid of each element. This paper presents various numerical examples in which the accuracy of the present method is verified. Comparisons have been made between the SIFs predicted by the GDC method and the available reference solutions in the current literature. A good agreement is achieved between the results of the GDC method and the reference solutions.

Mixed-mode fracture analysis of orthotropic functionally graded materials under mechanical and thermal loads

In advance composite material the propagation of crack is a regular failure problem in various engineering applications especially in aircrafts body. The aircraft body components are subjected to various thermal and mechanical loading conditions. It is very difficult, time-consuming and costly process of testing the aircrafts components failure due to various thermal and mechanical conditions. Strain energy release rate (SERR) is the significant parameter for the composite materials and quality of composite materials depends in SERR values.The present investigation is based on ANSYS analysis for finding the strain energy release rate (SERR) value using Virtual Crack Closure Technique (VCCT) to understand the fracture behavior of the composite lamina. The circular crack present in the middle of the composite plate and subjected to Pressure and temperature loading for different angle (cross-ply& and angle-ply) composite structure laminas. The angle-ply shows less SERR in mode I & II while cross-ply shows less SERR in mode III under the constant Pressure loading conditions. Mode II shows the maximum SERR in cross-ply compared to mode I and III for temperatures 30ºC,80ºC, 130 ºC & 180ºC. SERR for mixed-mode was found by considering the total mode of fracture and validation based on published literature for SERR due to the Thermal load of mode I (GI) for different fiber layup configurations of the circular cut-out.

The main objective of this paper is to identify different analytical methods which permit the calcula- tion of the stress level in wooden simply supported beams, due to mechanical and thermal loading conditions. Two different wood species, with different cross-sections, will be presented. The fi re resistance, the charring depth layer and the charring rate will be determined using the fi nite element method with Ansys® program. To characterize the stress state in wooden beams, all elements are subjected to mechanical load considering the reduction of the cross-section, infl uenced by thermal action. Another purpose of this work is to identify the ultimate safe load-bearing capacity in wooden beams, subjected to uniform load simultaneously with the thermal effect. All numerical results per- mit the specifi cation of simple design calculation methods, simplifying the verifi cation of the fi re safety of wooden beams. Wood is a renewable resource, recently attracting public attention, as an environmentally friendly material. This product is a building material with attractive attributes such as archi- tectural and structural characteristics. Wood is classifi ed in two different botanical terms. The botanical terms, softwoods and hardwoods, indicate the basic structure and cell type of mois- ture within the tree. Softwoods generally come from the coniferous species (pines, fi rs and spruces, for example) and are generally fi ne textured. Hardwoods (eucalypts and oaks, for example) have broad leaves and the texture ranges from fi ne to coarse. The types of wood include softwoods, hardwoods and glued laminated woods, in the forms of solid wood, ply- wood and wood-based panels. Due to large variation, type and wood quality, a system of strength classes was established. Each grade of classifi cation is a function of the physical and wood properties. The wood when exposed to accidental actions, such as ficonditions, pre- sents a surrounding charring layer. However, this layer can delay the heating process from the exposed side to the wood core section, acting as an insulating layer. The wood core section may remain at low temperatures, depending on the fi re exposure and element size therefore. It is important to calculate the value of charring rate and determine the thickness of char layer formation through the section. These parameters are important in fisafety design because they determine the residual load-bearing cross-section, due to critical external conditions. Safety rules and guidelines should be useful for different wooden structures. The high vulner- ability of wood, with respect to firequires a rigorous thermal and mechanical analysis. The study of fi re resistance of wood structures is therefore a topic of great interest. Several researchers have presented experimental and numerical models for the study of wood in the presence of high temperatures (1-3). The charring rate of softwood or hardwood material, exposed to fi conditions, has been studied in different countries, (4-11). Some empirical models for charring rate calculation have been developed by other researchers (4-6). The wood species considered in this work are the Fir subalpine and Redwood, from Northern Europe. These conifer species are widely used in construction, textile, paper- making, resin

Thermomechanical fatigue cracking in fiber reinforced metal-matrix composites

Thermo-mechanical XFEM crack propagation analysis of functionally graded materials

Modelling of a crack propagating through a finite element mesh under mixed mode conditions is of prime importance in fracture mechanics. In this paper, two crack growth criteria and the respective crack paths prediction in functionally graded materials (FGM) are compared. The maximum tangential stress criterion (et -criterion) and the minimum strain energy density criterion (S-criterion) are investigated using advanced finite element technique. Using Ansys Parametric Design Language (APDL), the variation continues in the material properties are incorporated into the model by specifying the material parameters at the centroid of each finite element. In this paper, the displacement extrapolation technique (DET) proposed for homogeneous materials is modified and investigated, to obtain the stress intensity factors (SIFs) at crack-tip in FGMs. Several examples are modeled to evaluate the accuracy and effectiveness of the combined procedure. The effect of the defects on the crack propagation in FGMs was highlighted.

The objective of this work is to present a numerical modeling of crack propagation path in functionally graded materials (FGMs) under mixed-mode loadings. The minimum strain energy density criterion (MSED) and the displacement extrapolation technique (DET) are investigated in the context of fracture and crack growth in FGMs. Using the Ansys Parametric Design Language (APDL), the direction angle is evaluated as a function of stress intensity factors (SIFs) at each increment of propagation and the variation continues of the material properties are incorporated by specifying the material parameters at the centroid of each finite element (FE). In this paper, several applications are investigated to check for the robustness of the numerical techniques. The defaults effect (inclusions and cavities) on the crack propagation path in FGMs are examined.

An existing axisymmetric analytical solution examines the radial and tangential thermal stresses and strains, and the radial displacements around a circular hole in a functionally graded material (FGM) plate. This solution is the point of departure to apply an inverse problem methodology to pose two inverse problems from measurements of the displacement and/or stress field: First, for known material distribution gradation function and material behavior the aim is to evaluate the thermal load. Second, for known thermal load and material behavior the objective is to define the gradation function coefficients relevant to determination of the properties. The inverse problem methodology explored in this paper for a FGM infinite plate with a hole provides a robust approach to determining the material gradation function and/or thermal loading conditions. It also demonstrates that careful attention needs to be paid to the analytical formulation of the behavior of FGMs so that the experimental necessity for evaluating and characterizing actual mechanical property variation inherent to these manufactured FGM structures may become a reality.

Analysis of crack problems in functionally graded materials under thermomechanical loading using graded finite elements

Functionally Graded Materials (FGM) have continuous variation of material properties from one surface to another unlike a composite which has stepped (or discontinuous) material properties. The gradation of properties in an FGM reduces the thermal stresses, residual stresses, and stress concentrations found in traditional composites. An FGM’s gradation in material properties allows the designer to tailor material response to meet design criteria. For example, the Space Shuttle utilizes ceramic tiles as thermal protection from heat generated during re-entry into the Earth’s atmosphere. However, these tiles are prone to cracking at the tile / superstructure interface due to differences in thermal expansion coefficients. An FGM made of ceramic and metal can provide the thermal protection and load carrying capability in one material thus eliminating the problem of cracked tiles found on the Space Shuttle. This paper will explore analysis of shell panels under thermal loading and compare performance of traditional homogeneous materials to FGMs using ABAQUS [1] finite element software. First, theoretical development of FGMs is presented. Second, finite element modeling technique for FGMs is discussed for a thermal stress analysis. Third, homogeneous curved panels made of ceramic and metal are analyzed under thermal loading. Finally, FGM curved panels created from a mixture of ceramic and metal are analyzed. FGM performance is compared to the homogeneous materials in order to explore the effect continuously grading material properties has on structural performance.

Investigating the graded-index influence on elastic responses of axisymmetric pressurized and heated thick-walled functionally graded material of cylindrical vessel

FEM model for stochastic mechanical and thermal postbuckling response of functionally graded material plates applied to panels with circular and square holes having material randomness

Postbuckling of FGM plates with piezoelectric actuators under thermo-electro-mechanical loadings