Noded Isoparametric Element Research Articles

Forced Motions of Composite Conoidal Shell Roofs with Complicated Boundary Conditions

An eight noded isoparametric finite element code is applied to study static bending, free and forced vibration characteristics of composite conoidal shell roofs with complicated boundary conditions which are often encountered in the industry.

Study of Static Characteristics of Delaminated Composite Conoidal Shell Subjected to Point Load

Delamination is one of the most common modes of defects of laminated composite shell roofs. A review of literature that exists on composite shells reveals that the research reports on delaminated shells are very few in numbers. Present paper deals with the static analysis of delaminated composite conoidal shells with simply supported boundary condition and subjected to centrally applied point load. For the present study work a finite element approach using eight noded isoparametric shell element with five degrees of freedom per node is employed. A multipoint constraint algorithm is incorporated, to satisfy compatibility of deformation and equilibrium of forces and moments, which leads to unsymmetrical stiffness matrix. This formulation is validated through solutions of benchmark problems. Lamination and extent of delamination area are varied to compare the performances of delaminated conoidal shells against those with no damage. Based on the present comparison some engineering conclusions are also included in this paper, which will serve as future reference.

Bending of Skewed Cylindrical Shell Panels

In this paper a nine node isoparametric plate bending element has been used for bending analysis of isotropic skewed cylindrical shell panels. Both thick and thin shell panels have been solved. In the present analysis first order shear deformation theory has been incorporated. The analysis has been performed considering shallow shell method. Both shallow and moderately deep shells have been solved. Skewed cylindrical shell panels having different types of transverse loads, shell thickness (h/a = 0.01 and 0.1), length to curvature ratios (a/R), skewed angle, and boundary conditions have been analyzed following shallow shell method.

Building frame-pile foundation-soil interactive analysis

The effect of soil-structure interaction on a simple single storeyed and two bay space frame resting on a pile group embedded in the cohesive soil (clay) with flexible cap is examined in this paper. For this purpose, a more rational approach is resorted to using the three dimensional finite element analysis with realistic assumptions. The members of the superstructure and substructure are descretized using 20 node isoparametric continuum elements while the interface between the soil and pile is modeled using 16 node isoparametric interface elements. Owing to viability in terms of computational resources and memory requirement, the approach of uncoupled analysis is generally preferred to coupled analysis of the system. However, an interactive analysis of the system is presented in this paper where the building frame and pile foundation are considered as a single compatible unit. This study is focused on the interaction between the pile cap and underlying soil. In the parametric study conducted using the coupled analysis, the effect of pile spacing in a pile group and configuration of the pile group is evaluated on the response of superstructure. The responses of the superstructure considered include the displacement at top of the frame and moments in the superstructure columns. The effect of soil-structure interaction is found to be quite significant for the type of foundation used in the study. The percentage variation in the values of displacement obtained using the coupled and uncoupled analysis is found in the range of 4-17 and that for the moment in the range of 3-10. A reasonable agreement is observed in the results obtained using either approach.

EXPERIMENTAL AND FINITE ELEMENT INVESTIGATION ON THE LOAD – SLIP BEHAVIOR OF COMPOSITE PUSH OUT SEGMENTS USING VARIOUS SHEAR CONNECTORS

a variety of composite steel-concrete column segments using shear connectors of different shapes and sizes to provide resistance to slip at steel – concrete interfaces . Hence , it represents a qualitative transition in the experimental and analytical investigations on shear connectors effectivity at steel – concrete interfaces , as most studies in the field of shear connectors were devoted to composite beam and slab – systems .Three types of shear connectors – with four concrete grades for each type – were used in fabricating composite specimens . The twelve composite prototypes were subjected to push – out test individually to examine their behavior by measuring the slip values for each load incremental till failure , thus determining the resistance extent of each connectors type and specifying the failure mode at interface .A nonlinear three – dimensional finite element analysis have been carried out on twelve composite column segments using ANSYS computer program (5 th version , 2882) to investigate their behavior and predict their load – slip relationships , equivalent stress distributions and concrete cracking patterns . The defined numerical modeling included using the eight node isoparametric brick element with smeared reinforcement (SOLID 55 ) and the eight node isoparametric steel brick element ( SOLID75) , to model the reinforced concrete medium and the steel section and shear connectors , respectively , considering perfect bond between concrete and steel reinforcing bars . Nonlinear properties including cracking and crushing of concrete , yielding of steel section and reinforcement , and nonlinear bond – slip at interface were also considered .Comparison of the experimental and theoretical results has shown good agreement that verifies the accuracy of the finite element model based on the smeared crack model of concreteResults have detected the development of the relative movement (slip) be at all ranges of the load-slip relationship at interface even with using effective shear connection and /or high quality concrete.The headed studs have revealed the highest slip resistance and ultimate load over the channel and the L-shaped studs . The high strength concrete has also revealed the same superiority over the other three tested types of concrete .

Experimental Investigation and Finite Element Analysis of Fatigue Crack Growth in Pipes Containing a Circumferential Semi-elliptical Crack Subjected to Bending

In this paper, a circumferential external surface flaw in a metallic round pipe under cyclic bending loading is considered. Because of very rapid changes in the geometrical parameters around the crack front region, the mesh generation of this region must be done with great care. This may lead to an increase in the run time which makes it difficult to reach valid results and conclusions. Because of the advantages of the sub-modeling technique in problems which need very high mesh density, this method is used. Stress intensity factors in mode I condition are determined using three-dimensional finite element modeling with 20 node iso-parametric brick elements in the ANSYS 9.0 standard code and the singular form of these finite elements at the crack front. In order to estimate the analysis error, the structural parameter error in energy norm criterion was used. Because of the advantages of non-dimensional analysis, this method is employed, and the stress intensity factors are normalized. For the analysis of the fatigue crack growth, the Paris law is used. The propagation path of the surface flaw is obtained from the diagram of aspect ratio versus relative crack depth. The fatigue crack growth analysis (the relative crack depth against loading cycles diagram) of different initial crack aspect ratio under cyclic loading is also considered. Fatigue shape development of initially semi-elliptical external surface defects is illustrated. The effect of the Paris exponent (material constant) on fatigue crack propagation is shown as well. Moreover, the fatigue crack growth of several specimens is assessed experimentally using a manually-constructed experimental set up. Finally, the experimental results obtained by cyclic bending loading tests are compared with the numerical results. The experimental results show good conformity with the finite element results.

Comparison between Experimental and 3D Finite Element Analysis of Reinforced and Partially Pre-Stressed Concrete Solid Beams Subjected to Combined Load of Bending, Torsion and Shear

This paper presents a non-linear analysis of three reinforced and two partially prestressed concrete solid beams based on a 20 node isoparametric element using an in-house 3D finite element program. Anon linear elastic isotropic model, proposed by Kotsovos, was used to model concrete behaviour, while steel was modelled as an embedded element exhibiting elastic-perfectly plastic response. Allowance was made for shear retention and for tension stiffening in concrete after cracking. Only in a fixed direction, smeared cracking modelling was adopted. The beams dimensions were 300x300 mm cross section, 3800 mm length and were subjected to combined bending, torsion and shear. Experimental results were compared with the non-linear predictions. The comparison was judged by load displacement relationship, steel strain, angle of twist, failure load, crack pattern and mode of failure. Good agreement was observed between the predicted ultimate load and the experimentally measured loads. It was concluded that the present program can confidently be used to predict the behaviour and failure load of reinforced and partially prestressed concrete solid beams subjected to a combined load of bending, torsion and shear.

Failure Analysis of Laminated Composite Plates under Linearly Varying Temperature

The present paper deals with the first ply failure analysis of laminated composite plates under linearly varying temperature through the thickness of the laminate. The plate element has been modeled as an eight noded isoparametric quadratic plate bending element based on Reissner-Mindlin's assumption for the transverse shear deformation. The deflection and stress resultants obtained in the present study are compared with those available in published literature. The stress level causing the failure of the weakest layer has been detected, based on various stress interactive failure criteria viz. Tsai-Wu and Hoffman's criteria. The temperature of the outermost layer has been computed at the stress level of that weakest ply failure. A parametric study has been carried out on the basis of different lamination schemes and boundary conditions.

A new approach for the large deflection finite element analysis of isotropic and composite plates with arbitrary orientated stiffeners

A new approach for the large deflection analysis of isotropic and composite arbitrary orientated stiffened plates is presented. Non-linear equilibrium equations are derived using the principle of virtual work applied to a continuum with a total Lagrangian description of motion. Eight node isoparametric plate elements are combined with three node beam elements, using the concept of equal displacements at the plate–stiffener interface, to represent the stiffened plate. The stiffness of the beam element is computed first irrespective of its position within the plate element and then transferred to the plate nodes depending on its orientation and position within the plate element. The Newton–Raphson incremental-iterative solution technique is used to obtain the non-linear response path. Results obtained by the present approach are compared with those available in the open literature to demonstrate the validity and efficiency of the proposed approach and good agreement is found in all the investigated cases.

Static stability of laminated composite circular plates with holes using shear deformation theory

The behavior of buckling of laminated composite circular plates having circular holes and subjected to uniform radial load is investigated by using the finite element method. A finite element analysis program was developed to analyze static stability. Eight node isoparametric shell elements with 24 degrees of freedom are used during the investigation. The first-order shear deformation theory is used to consider the effects of the transverse shear deformation. The effects of hole sizes, location of the holes, thickness variations and boundary conditions on the buckling load of the composite plates are determined.

EFFECTIVE STRESS FINITE ELEMENT ANALYSIS OF PILE-SOIL INTERACTION PROBLEMS

The effective stress method is developed to predict the axial capacity of piles in clay. This method is based on the principle that, at failure, the available shear resistance at the pile soil interface is related to the mean normal effective stress at the pile face and the effective stress friction angle for the soil sliding on the pile material. In this paper, the coupled non-linear finite element method is used to analyze some pile-soil interaction problems. This computer program ( CRISP ) is used for this task. Eight- node isoparametric elements were used for displacements while four- node elements are used for pore pressure. Interface elements are used to simulate the interaction between the pile and the soil. The soil is assumed to follow different models, linear elastic and modified Cam-clay model. A comparison is made between the measured and predicted settlements and excess pore water pressures and good convergence was obtained in which the proposed technique used in this paper, in which the measured excess pore water pressures are considered as initial pore pressures in the computer program ( CRISP ). No load was applied on the pile. The dissipation of excess pore water was studied through carrying out consolidation analysis.

EFFECTIVE STRESS FINITE ELEMENT ANALYSIS OF PILE-SOIL INTERACTION PROBLEMS

The effective stress method is developed to predict the axial capacity of piles in clay. Thismethod is based on the principle that, at failure, the available shear resistance at the pile soilinterface is related to the mean normal effective stress at the pile face and the effective stressfriction angle for the soil sliding on the pile material.In this paper, the coupled non-linear finite element method is used to analyze some pile-soilinteraction problems. This computer program ( CRISP ) is used for this task. Eight- nodeisoparametric elements were used for displacements while four- node elements are used forpore pressure. Interface elements are used to simulate the interaction between the pile and thesoil. The soil is assumed to follow different models, linear elastic and modified Cam-claymodel. A comparison is made between the measured and predicted settlements and excesspore water pressures and good convergence was obtained in which the proposed techniqueused in this paper, in which the measured excess pore water pressures are considered as initialpore pressures in the computer program ( CRISP ). No load was applied on the pile. Thedissipation of excess pore water was studied through carrying out consolidation analysis.

Buckling Analysis of Laminated Composite Circular Plates with Holes

In this study, buckling analysis of laminated composite circular plates having circular holes and subjected to uniform radial load is investigated by using the finite element method. The effects of hole sizes, location of the holes, thickness variations and boundary conditions on the critical buckling load, and the buckling mode shapes of the composite plates are determined. Eight node isoparametric shell elements with 24 degrees of freedom are used during the investigation.

Stress intensity factors in a hollow cylinder containing a circumferential semi-elliptical crack subjected to combined loading

The problem of mixed mode fracture induced by a semi-elliptical circumferential crack lying at the outer surface of the cross-section of a hollow cylinder is considered. The cylinder is under the action of axial force, bending moment and torsion. To make the results comprehensive, dimensionless analysis is used, and a large variation limit of parameters that define the crack geometry is considered. Because of the advantages of the sub-modeling technique in problems which need very high mesh density, this method is used. Stress intensity factors in mixed mode condition are determined using three-dimensional finite element modeling with 20 node-isoparametric elements and the singular form of these finite elements at the crack front. The obtained results show to be in good accordance with those cited in the literature for the cases of separate application of axial load and bending moment. However, when torsion is added to tension and bending moment, a non-symmetrical distribution of stress intensity factor along the crack front is observed which can cause non-symmetric fatigue crack propagation.

Free vibration analysis of delaminated composite pretwisted shells

PurposeTo investigate the effects of delamination on free vibration characteristics of graphite‐epoxy composite pretwisted cylindrical shallow shells of various stacking sequences considering length of delamination as a parameter.Design/methodology/approachA multipoint constraint algorithm which leads to unsymmetric elastic stiffness matrix is incorporated into an eight noded isoparametric plate bending finite element to satisfy the compatibility of deformation and equilibrium of resultant forces and moments at the delamination crack front. The study is focused upon long, intermediate and short cylindrical shells as defined by Aas‐Jakobsen's parameters and considers symmetric and unsymmetric composite laminates.FindingsThe non‐dimensional fundamental natural frequencies are obtained for angle ply (45/−45/45, 45/−45) and cross ply (0/90/0, 0/90) configurations corresponding to different crack lengths and twist angles. The study implies the importance of the symmetric laminate as well as the long shell.Research limitations/implicationsThe standard eigenvalue computations using QR iteration algorithm for the present analyses take enormous time and hence, an efficient eigen‐solver needs to be employed.Practical implicationsNew vibration modes are exhibited by the delaminated composite structures. The existence of invisible interlaminar cracking can be identified with the help of prior knowledge of natural frequencies for a delaminated composite pretwisted shell which can be idealized as a turbine blade with low aspect ratio.Originality/valueThis paper presents a numerical approach for natural frequency determination of composite pretwisted shallow shells having delamination without taking care of the effect of dynamic contact between delaminated layers. The non‐dimensional frequencies obtained could serve as reference solutions for future investigators.

A genetic algorithm based back propagation network for simulation of stress–strain response of ceramic-matrix-composites

Ceramic-matrix-composites (CMCs) are fast replacing other materials in many applications where the higher production costs can be offset by significant improvement in performance. In applications such as cutting and forming tools, wear parts in machinery, nozzles, valve seals and bearings, improvement in toughness and hardness translate into longer life. However, the recent resurgence in the field of development of CMCs has been due to their potential use for the Space Transport systems, Combustion engines and other energy conversion systems. The CMCs are ideal structural material for these applications. However, due to their lack of toughness, they are prone to brittle fractures. Therefore, the main consideration in the development of CMCs has been to toughen them. To achieve this, the bi-material interface should be weak and must allow debonding, resulting in crack deflection. In the present work, the stress–strain response of Al 2O 3 (matrix)/SiC (whisker) ceramic composite has been simulated using a back propagation neural network (BPN), which incorporates the effect of interface shear strength (IFS) in the analysis. For efficient and quick training, the weights for the BPN have been obtained by using a genetic algorithm (GA). The GA has been modelled with 150 genes and a chromosome string length of 750. The network simulation is based on the stress–strain response obtained from the finite element analysis. A three noded isoparametric interface element has been employed to model the whisker/matrix interface in finite element analysis. The finite element analysis has been carried out only for a limited number of specimens. However, the simulation model is capable of predicting the stress–strain relationship for a new interface shear strength even with this limited information. Thus, the robustness and the generalisation capability of the neural network model is demonstrated. The development stages of the GA/BPN model such as the preparation of training set, selection of a network configuration, training of the net and a testing scheme, etc., have been addressed at length in this paper.

Nonlinear impact behaviour of laminated composite shells in hygrothermal environments

The nonlinear transient response of laminated composite shell panels subjected to low velocity impact in hygrothermal environments is investigated using finite element method. The present formulation considers doubly curved thick shells and includes large deformations with Green- Lagrange strains. The analysis is carried out using quadratic eight—noded isoparametric element. A modified Hertzian contact law is incorporated into the finite element program to evaluate the impact force. The nonlinear equation is solved using the Newmark average acceleration method in conjunction with an incremental modified Newton-Raphson scheme. The validity of the present analysis is demonstrated by comparing the present results with the solutions available in the literature. A parametric study is carried out to investigate the effects of the curvature and side to thickness ratios of simply supported composite cylindrical and spherical shell panels.

Bending Characteristics of Thick Multidirectional Composite Plates under Hygrothermal Environment

Effects of moisture and temperature on the bending characteristics of thick multidirectional fibrous composite plates are studied. A three-dimensional finite element analysis procedure is developed using twenty noded isoparametric quadratic brick elements. A typical multidirectional unit cell is assumed to consist of several unidirectional composite blocks. Transformation-based relationships are used to generate the stiffness properties of a multidirectional composite model. The FE analysis accounts for the hygrothermal strains and reduced elastic properties of multidirectional composites at an elevated moisture concentration and temperature. Deflections and stresses are evaluated for thick multidirectional composite plates under uniform and linearly varying through-the-thickness temperature and moisture content. Results reveal the effects of fiber directionality on deflection and stresses.

Finite Element Analysis of Smart Structures Containing Piezoelectric Fiber-Reinforced Composite Actuator

Static analysis of laminated smart composite plates integrated with a piezoelectric fiber-reinforced composite (PFRC) layer acting as distributed actuators has been carried out by a generalized-energy-based finite element model. A simple first-order shear deformation theory is used for deriving the model. Eight noded isoparametric serendipity elements are used for discretizing the domain. The performance of the PFRC layer has been investigated for both symmetric and antisymmetric cross-ply and antisymmetric angle-ply laminated composite shell substrates. The effect of piezoelectric fiber orientation on the control authority of the PFRC layer has also been studied.

액체 로켓 터보 펌프 터빈의 천이 열전달 및 구조 해석

유한요소법을 이용하여 액체 로켓 엔진 터보 펌프 터빈의 천이 열전달 및 구조 해석이 수행되었다. 해석 모델은 3차원 8절점 등매개변수 솔리드 요소로 구성되었으며, 전체 모델의 1/80만이 해석되었다. 열 스파이크를 포함하는 시동 조건과 정상상태에서의 하중이 고려되었다. 블레이드 면 위의 열전달 계수는 상용 열유동 해석 프로그램인 Fluent를 이용하였다. 개발된 유한 요소 코드를 이용하여 시동 및 정상상태에서 천이 열전달 응답을 구하였다. 또한, 원심력과 열하중이 가해질 때, 최대 응력 및 슈라우드의 변위를 구하였다. Thermal and structural finite element analyses were performed for the turbopump turbine bladed disk model with shroud of a liquid rocket engine. The only 1/80 part model was analyzed which consists of 3D eight node isoparametric solid elements. The applied loading history consists of a startup condition with a thermal spike and a steady state. Heat transfer coefficient on the blade was predicted using the commercial Navier-Stokes solver, Fluent. Transient thermal responses during startup and steady states were calculated using a 3D finite element code developed. Maximum stress and shroud tip displacement under the influence of centrifugal and thermal loading were also determined.