Numerical Simulations of Stiffened Panels under Compressive Loads and Structural Analyses of Midship Section

2012 ◽  
Author(s):  
Evangelos Koutsolelos
Keyword(s):  
Finite Element ◽  
Numerical Simulations ◽  
Structural Integrity ◽  
Finite Element Analyses ◽  
Structural Components ◽  
Ship Structures ◽  
Stiffened Panels ◽  
Compressive Loads

In this paper, structural integrity of ship structures is discussed using Finite Element analyses. Buckling behaviors of shell structural components are investigated taking into account geometric and material nonlinearities. Recommendations are made to Naval Architects based on tools developed throughout the research.

The development of design guidelines for integrally stiffened panels under compression using surrogate modelling

2017 ◽  
Vol 233 (3) ◽  
pp. 779-792
Author(s):  
Morteza Dezyani ◽  
Shahram Yousefi ◽  
Hossein Dalayeli ◽  
Hamid Frrokhfal
Keyword(s):  
Finite Element ◽  
Global Optimum ◽  
Initial Guess ◽  
Design Guidelines ◽  
Programming Algorithm ◽  
Preliminary Design ◽  
Finite Element Analyses ◽  
Surrogate Modelling ◽  
Stiffened Panels ◽  
Integrally Stiffened Panels

Preliminary design of stiffened compression panels used in aerospace structures is commonly based on the routine analytical and semi-empirical equations. Empirical charts are used for obtaining an initial guess to start the preliminary design process. In this paper, preliminary design guidelines for stiffened compression panels are developed based on the non-linear finite element analyses. Meanwhile, the process of design and optimization of the stiffened compression panels are carried out. Modelling phase is based on the finite element simulations of the structure. The surrogate modelling technique is employed to reduce the number of finite element analyses. An efficient technique is developed to find the global optimum of the surrogate model using sequential quadratic programming algorithm. The proposed approach is applied to two types of integrally stiffened panels. The final results are extracted as practical design guidelines which are suitable for preliminary design phase.

Estimate of the Ultimate Load on Structural Members Subjected to Lateral Loads

2001 ◽  
Vol 38 (03) ◽  
pp. 169-176
Author(s):  
L. Belenkiy ◽  
Y. Raskin
Keyword(s):  
Finite Element ◽  
Limit Analysis ◽  
Ultimate Load ◽  
Limit Load ◽  
Plastic Behavior ◽  
Lateral Loads ◽  
Ship Structures ◽  
Strength Assessment ◽  
Stiffened Panels ◽  
Plate Elements

This paper examines plastic behavior of typical ship structures, specifically beams, grillages, and plates subjected to predominantly lateral loads. The ultimate loads, determined on the basis of the theorems of limit analysis [1,2], are evaluated using nonlinear finite-element plastic analysis. The relationships between analytical and finite-element models for prediction of ultimate loads of beams, stiffened panels, and grillages are illustrated. It has been shown that the ultimate loads, obtained from the theorems of limit analysis, can be successfully used for strength assessment of stiffened ship structures subjected to lateral loads. The effect of shear force on ultimate load is analyzed using the finite-element method. This paper confirms that in the case of beams and grillages under lateral loading, the ultimate load may characterize the threshold of the load at which a stiffened ship's structure fails by the development of excessive deflections. For plate elements, on the other hand, the plastic deflections represent the permissible limit of external load better than the ultimate limit load.

Simplified Assessment of Studs Allowing for Low Constraint Conditions

2017 ◽  
Author(s):  
P. James ◽  
C. Madew ◽  
M. Jackson
Keyword(s):  
Fracture Toughness ◽  
Finite Element ◽  
Structural Integrity ◽  
High Stress ◽  
Pressure Vessels ◽  
Materials Testing ◽  
Screw Thread ◽  
Surface Point ◽  
Finite Element Analyses ◽  
Supporting Materials

Defect tolerance assessments are carried out to support the demonstration of structural integrity for high integrity components such as nuclear reactor pressure vessels. These assessments often consider surface-breaking defects and assess Stress Intensity Factors (SIFs) at both the surface and deepest points. This can be problematic when there is a high stress at the surface, for example due to the stress concentration at the root of a screw thread. In the past this has led to the development of complex and costly 3D finite element analyses to calculate more accurate SIFs, and still resulting in small apparent limiting defect sizes based on initiation at the surface point. Analysis has been carried out along with supporting materials testing, to demonstrate that the increased SIF at the surface point is offset by a reduction in crack-tip constraint, such that the material exhibits a higher apparent fracture toughness. This enables a more simplistic assessment which reduces the effective SIF at the surface such that only the SIF at the deepest point needs to be considered for many defects. This then leads to larger calculated limiting defect sizes. This in turn leads to a more robust demonstration of structural integrity, as the limiting defect sizes are consistent with the capability of non-destructive examination techniques. An overview of the supporting materials testing is provided in an accompanying paper. The accompanying paper details how it was not possible to demonstrate the required material response with conventional tests, such as those using shallow-notched bend specimens. Instead it was necessary to develop modified specimens in which semi-elliptical defects were introduced into a geometry which replicated the notch acuity at the root of a screw thread. These tests were used to quantify the stud materials sensitivity to constraint. Conventional three-point bend tests were also seen to confirm these values. A series of R6 constraint modified assessments have been considered to understand the benefit from including a loss of constraint, particularly when assessing the surface breaking SIF. This has necessitated a series of complex finite element analyses to define the elastic SIF as well as the elastic constraint parameter, T-Stress, T. Further verification analyses have also been performed to determine the equivalent elastic-plastic J and Q parameters. These have been used to provide guidance on how best to assess surface breaking defects within studs. This has shown that the increased perceived toughness at the surface location means that under the majority of conditions, the assessment can simply be based upon the SIF at the depth location using high constraint fracture toughness. This paper provides an overview of the process undertaken to provide simplified guidance on assessing defects within studs that allows benefit from constraint loss.

scholarly journals Engineering Studies on Joint Bar Integrity: Part I — Field Surveys and Observed Failure Modes

2014 ◽  
Author(s):  
David Y. Jeong ◽  
Radim Bruzek ◽  
Ali Tajaddini
Keyword(s):  
Finite Element ◽  
Failure Modes ◽  
Structural Integrity ◽  
Transportation Systems ◽  
Finite Element Analyses ◽  
Research Project ◽  
Field Surveys ◽  
Technology Center ◽  
Survey Team ◽  
Engineering Studies

This paper is the first of a two-part series describing a research project, sponsored by the Federal Railroad Administration (FRA), to study the structural integrity of joint bars. In Part I of this series, observations from field surveys conducted on revenue service track are presented. Automated and visual inspections of rail joints were conducted to identify defective joint bars. Detailed information and measurements were collected at various joint locations. The survey team consisted of personnel from ENSCO, Inc. and Transportation Technology Center, Inc. (TTCI), working in cooperation with staff from participating railroads. Part II of this series describes the development of finite element analyses of jointed rail, which is being carried out by the Volpe National Transportation Systems Center (Volpe Center).

Limit Analysis for Anisotropic Solids Using Variational Principle and Repeated Elastic Finite Element Analyses

2002 ◽  
Author(s):  
L. Pan ◽  
R. Seshadri
Keyword(s):  
Finite Element ◽  
Variational Principle ◽  
Limit State ◽  
Limit Load ◽  
Anisotropic Materials ◽  
Stress Fields ◽  
Finite Element Analyses ◽  
Structural Components ◽  
Directionally Solidified ◽  
Elastic Compensation Method

Many structural components, such as rolled sheets, directionally solidified superalloys and composites, are made of anisotropic materials. The knowledge of limit load is useful in the design and the sizing of these components and structures. This paper presents the extension of the modified mα-method to anisotropic materials. Mura’s variational principle is employed in conjunction with repeated elastic finite element analyses (FEA). The secant modulus of the discretized finite elements in the reference direction in successive elastic iterations is used to estimate the plastic flow parameter for the anisotropic components. The modified initial elastic properties are adopted to ensure the “elastic” stress fields satisfy the anisotropic yield surface. Using the notion of “leap-frogging” to limit state, improved lower-bound limit loads can be obtained. The formulation is applied to two anisotropic components, and the limit load estimates are compared with those using elastic compensation method and inelastic FEA.

Magnitude and Distribution of Retained Residual Stresses in Laboratory Fracture Mechanics Specimens Extracted From Welded Components

2012 ◽  
Author(s):  
R. G. Hurlston ◽  
J. K. Sharples ◽  
A. H. Sherry
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Fracture Mechanics ◽  
Residual Stresses ◽  
Structural Integrity ◽  
Specimen Size ◽  
Finite Element Analyses ◽  
Structural Components ◽  
Stress Partitioning ◽  
Material Fracture

Quantifying material fracture toughness properties is an important step in ensuring structural integrity of industrial components. Welding of structural components can cause large magnitudes of residual stress to be generated, which can be defined as a stress that exists in a material when it is under no primary loading. These stresses can be retained in laboratory fracture mechanics testing specimens removed from non-stress relieved welds, making the quantification of valid material fracture toughness difficult. The aim of this paper is to investigate, analytically, the levels and distributions of residual stresses retained in fracture mechanics specimens taken from welded components. This was achieved using parametric finite element analyses. Furthermore, in order to ensure the validity of fracture toughness measurements derived from components that contain residual stress, a robust method for the design of stress-free fracture mechanics specimens is proposed. Significant weld residual stresses have been shown to be retained in certain laboratory specimens post extraction from non stress-relieved welds. The magnitude and distribution of retained residual stress has been shown to be dependant on material properties, specimen size, specimen type and removal location. In addition, the stress partitioning method has been shown to provide a useful approach for estimating the levels and distributions of residual stresses retained in fracture mechanics specimens extracted in certain orientations.

scholarly journals Structural Integrity of Conventional and Modified Railroad Bearing Adapters for Onboard Monitoring

2014 ◽  
Author(s):  
Joseph Montalvo ◽  
Alexis Trevino ◽  
Arturo A. Fuentes ◽  
Constantine M. Tarawneh
Keyword(s):  
Finite Element ◽  
Structural Integrity ◽  
Element Model ◽  
Operating Conditions ◽  
Finite Element Analyses ◽  
Distribution Maps ◽  
Bearing Condition Monitoring ◽  
Monitoring Applications ◽  
Railroad Bearing ◽  
The Impact

This paper presents a detailed study of the structural integrity of conventional and modified railroad bearing adapters for onboard monitoring applications. Freight railcars rely heavily on weigh bridges and stations to determine cargo load. As a consequence, most load measurements are limited to certain physical railroad locations. This limitation provided an opportunity for an optimized sensor that could potentially deliver significant insight on bearing condition monitoring as well as load information. Bearing adapter modifications (e.g. cut-outs) were necessary to house the sensor and, thus, it is imperative to determine the reliability of the modified railroad bearing adapter, which will be used for onboard health monitoring applications. To this end, this study quantifies the impact of the proposed modifications on the adapter structural integrity through a series of experiments and finite element analyses. The commercial software Algor 20.3TM is used to conduct the stress finite element analyses. Different loading scenarios are simulated with the purpose of obtaining the conventional and modified bearing adapter stresses during normal and abnormal operating conditions. This information is then used to estimate the lifetime of these bearing adapters. Furthermore, this paper presents an experimentally validated finite element model which can be used to attain stress distribution maps of these bearing adapters in different service conditions. The maps are also useful for identifying areas of interest for an eventual inspection of conventional or modified railroad bearing adapters in the field.

Engineering Studies on Joint Bar Integrity: Part II — Finite Element Analyses

2014 ◽  
Author(s):  
Michael E. Carolan ◽  
David Y. Jeong ◽  
A. Benjamin Perlman
Keyword(s):  
Finite Element ◽  
Structural Integrity ◽  
Structural Response ◽  
Relative Effect ◽  
Structural Performance ◽  
Finite Element Analyses ◽  
Field Surveys ◽  
Engineering Studies ◽  
Toe Angle ◽  
Support Conditions

This paper is the second in a two-part series describing research sponsored by the Federal Railroad Administration (FRA) to study the structural integrity of joint bars. In Part I, observations from field surveys of joint bar inspections conducted on revenue service track were presented [1]. In this paper, finite element analyses are described to examine the structural performance of rail joints under various loading and tie-ballast support conditions. The primary purpose of these analyses is to help interpret and understand the observations from the field surveys. Moreover, the finite element analyses described in this paper are applied to conduct comparative studies and to assess the relative effect of various factors on the structural response of jointed rail to applied loads. Such factors include: discrete tie support (i.e. supported joint versus suspended joint with varying spans between effective ties), bolt pattern (four versus six bolts), initial bolt tension, and easement. In addition, results are shown for 90 lb rail joined with long-toe angle bars compared to 136 lb rail joined with standard short-toe joint bars.

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