Dynamic Stresses During Structural Impacts

2003 ◽  
Author(s):  
Robert A. Leishear ◽  
Jeffrey H. Morehouse
Keyword(s):  
Maximum Stress ◽  
Plastic Material ◽  
Material Behavior ◽  
Solution Technique ◽  
Dynamic Stresses ◽  
Conservation Of Energy ◽  
Linear Elastic ◽  
Bending Stresses ◽  
Structural Impacts ◽  
Energy Principles

Dynamic stresses that occur when an object strikes a structure can be described by considering both vibration theory and conservation of energy principles. An object striking a simple beam is used as one of several examples. The complete stresses are found by adding the stresses obtained from a vibration equation to the stresses found by using a conservation of energy equation. When combined, these two stresses establish the maximum stress in a structure subject to impact. This solution assumes that each point within the beam acts as a linear system, reacting to the dynamic application of a load to the structure. When struck, the surface of the beam is momentarily compressed, and the beam bends. The equations describe both the localized stresses at the point of impact and the bending stresses in the beam following impact. These equations are then extended to an elastoplastic case, using a bilinear model to describe the dual natured linear elastic and linear plastic material behavior. The general solution technique is applicable to cases other than the simple beam.

Technical Basis for Characterization of Multiple Closely Separated Flaws Located in Different Planes

2017 ◽  
Author(s):  
Sébastien Blasset ◽  
Tomas Nicak ◽  
Elisabeth Keim ◽  
Ralf Tiete ◽  
Florian Obermeier
Keyword(s):  
Plastic Material ◽  
Material Behavior ◽  
Specific Work ◽  
3D Numerical Modeling ◽  
Elastic Plastic ◽  
Linear Elastic ◽  
Current Interaction ◽  
Elastic Plastic Material ◽  
Technical Basis ◽  
Non Destructive

Non-destructive inspection records have to be characterized before evaluation of acceptance if they are evaluated as material or fabrication flaws. When multiple flaws are detected by volumetric examination, the question of interacting flaws arises if they are close to each other: can the conventional approach based on individual flaw be applied? Alternative flaw characterization requirements may be applied in lieu of using current codes by considering recent fracture mechanics research. In order to relax the conservatism of current interaction criteria, specific work was performed to describe interaction rules for flaws located in different planes. The proximity criteria are valid for linear elastic or limited elastic plastic material behavior : this is generally the case in large components. This paper presents the technical basis including validation of the proximity criteria based on a specific component with several flaws and considering 3D numerical modeling using elastic-plastic material behavior in order to check if the plastic material behavior affects the selected proximity criteria. The component is submitted to uniform (pressure) and non-uniform loading (like thermal shock).

A Viscoelastic Correspondence Principle for Plane Membranes Subjected to Lateral Pressure

1983 ◽  
Vol 50 (4a) ◽  
pp. 740-742 ◽  
Author(s):  
B. Stora˚kers
Keyword(s):  
Time Dependence ◽  
Viscoelastic Material ◽  
Lateral Pressure ◽  
Correspondence Principle ◽  
Material Model ◽  
Material Behavior ◽  
Linear Elastic Material ◽  
First Order ◽  
Linear Elastic ◽  
Consistent Approximation

The classical Fo¨ppl equations, governing the deflection of plane membranes, constitute the first-order consistent approximation in the case of linear elastic material behavior. It is shown that despite the static and kinematic nonlinearities present, for arbitrary load histories a correspondence principle for viscoelastic material behavior exists if all relevant relaxation moduli are of uniform time dependence. Application of the principle is illustrated by means of a popular material model.

Shakedown Limit Load Determination for a Kinematically Hardening 90-Degree Pipe Bend Subjected to Constant Internal Pressure and Cyclic Bending

2007 ◽  
Author(s):  
Hany F. Abdalla ◽  
Mohammad M. Megahed ◽  
Maher Y. A. Younan
Keyword(s):  
Finite Element ◽  
Internal Pressure ◽  
Plastic Material ◽  
Kinematic Hardening ◽  
Limit Load ◽  
Material Behavior ◽  
Pipe Bend ◽  
Cyclic Bending ◽  
Perfectly Plastic ◽  
Shakedown Limit

A simplified technique for determining the shakedown limit load of a structure employing an elastic-perfectly-plastic material behavior was previously developed and successfully applied to a long radius 90-degree pipe bend. The pipe bend is subjected to constant internal pressure and cyclic bending. The cyclic bending includes three different loading patterns namely; in-plane closing, in-plane opening, and out-of-plane bending moment loadings. The simplified technique utilizes the finite element method and employs small displacement formulation to determine the shakedown limit load without performing lengthy time consuming full cyclic loading finite element simulations or conventional iterative elastic techniques. In the present paper, the simplified technique is further modified to handle structures employing elastic-plastic material behavior following the kinematic hardening rule. The shakedown limit load is determined through the calculation of residual stresses developed within the pipe bend structure accounting for the back stresses, determined from the kinematic hardening shift tensor, responsible for the translation of the yield surface. The outcomes of the simplified technique showed very good correlation with the results of full elastic-plastic cyclic loading finite element simulations. The shakedown limit moments output by the simplified technique are used to generate shakedown diagrams of the pipe bend for a spectrum of constant internal pressure magnitudes. The generated shakedown diagrams are compared with the ones previously generated employing an elastic-perfectly-plastic material behavior. These indicated conservative shakedown limit moments compared to the ones employing the kinematic hardening rule.

Influence From Helical Strakes on Vortex Induced Vibrations and Static Deflection of Drilling Risers

2005 ◽  
Author(s):  
Carl M. Larsen ◽  
Gro Sagli Baarholm ◽  
Halvor Lie
Keyword(s):  
Dynamic Response ◽  
Test Data ◽  
Oscillation Amplitude ◽  
Cross Flow ◽  
Current Profile ◽  
Dynamic Stresses ◽  
Drag Forces ◽  
Vortex Induced Vibrations ◽  
Bending Stresses ◽  
Helical Strakes

Helical strakes are known to reduce and even eliminate the oscillation amplitude of vortex induced vibrations (VIV). This reduction will increase fatigue life, and also reduce drag magnification from cross-flow vibrations. But sections with strakes will also have a larger drag coefficient than the bare riser. Hence, the extension of a section with strakes along a riser should be large enough to reduce oscillations, but not too long in order to limit drag forces from current and waves. The optimum length and position for a given riser will therefore vary with current profile. Dynamic response from waves should also be taken into account. The purpose of the present paper is to illustrate the influence from strakes on VIV, as well as on static and dynamic response for a drilling riser. Hydrodynamic coefficients for a cylinder with helical strakes are found from experiments and applied in an empirical model for the analysis of VIV. The result from the VIV analysis is used for a second calculation of drag forces that are applied in an updated static analysis. Dynamic stresses from regular waves are also presented, but VIV are not considered for these cases. A simple study of length and position of the section with strakes is carried out for some standard current profiles. Results are presented in terms of oscillation amplitudes, fatigue damage, bending stresses and riser angles at ends. The study is based on test data for one particular strake geometry, but the analysis method as such is general, and the computer programs used in the study can easily apply other test data.

scholarly journals NUMERICAL MODELLING OF THE SOIL BEHAVIOUR BY USING NEWLY DEVELOPED ADVANCED MATERIAL MODEL

2017 ◽  
Vol 57 (1) ◽  
pp. 58-70 ◽  
Author(s):  
Jan Veselý
Keyword(s):  
Numerical Modelling ◽  
Plastic Material ◽  
Material Model ◽  
Small Strain ◽  
Theoretical Background ◽  
Linear Elastic ◽  
In Situ Data ◽  
Modified Cam Clay ◽  
Soil Behaviour

This paper describes a theoretical background, implementation and validation of the newly developed Jardine plastic hardening-softening model (JPHS model), which can be used for numerical modelling of the soils behaviour. Although the JPHS model is based on the elasto-plastic theory, like the Mohr-Coulomb model that is widely used in geotechnics, it contains some improvements, which removes the main disadvantages of the MC model. The presented model is coupled with an isotopically hardening and softening law, non-linear elastic stress-strain law, non-associated elasto-plastic material description and a cap yield surface. The validation of the model is done by comparing the numerical results with real measured data from the laboratory tests and by testing of the model on the real project of the tunnel excavation. The 3D numerical analysis is performed and the comparison between the JPHS, Mohr-Coulomb, Modified Cam-Clay, Hardening small strain model and monitoring in-situ data is done.

scholarly journals Plastic composites made from glycerol, citric acid, and forest components

BioResources ◽  
2018 ◽  
Vol 13 (3) ◽  
pp. 6600-6612
Author(s):  
Rasika L. Kudahettige-Nilsson ◽  
Henrik Ullsten ◽  
Gunnar Henriksson
Keyword(s):  
Citric Acid ◽  
Maximum Stress ◽  
Plastic Material ◽  
Ash Content ◽  
Wood Powder ◽  
Renewable Materials ◽  
Amorphous Cellulose ◽  
Mechanical Pulp ◽  
3D Printers ◽  
Absorption Level

An ecofriendly approach for the synthesis of plastic biomaterials based on renewable materials suitable for 3D printing application or other applications has been developed. The material was prepared from native (microcrystalline) or amorphous cellulose, citric acid, and glycerol or ethylene glycol, by a pretreatment at 40 °C and a curing at 175 °C for 1 h. The results showed that tensile properties and the water absorption level of the material were acceptable. The highest strain at break (14%) was obtained from materials made of 10% amorphous cellulose with 90% glycerol/citric acid. It had a maximum stress at 37 MPa. Moreover, materials were without ash content. Possible applications of the material in 3D-printers were discussed. In addition, application of mechanical pulp and wood powder into novel plastic material production was discussed. Foaming during curing might be a problem for this type of material, but this can be avoided by using amorphous cellulose in the recipe.

A Microstructure-Level Material Model for Simulating the Machining of Carbon Nanotube Reinforced Polymer Composites

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Ashutosh Dikshit ◽  
Johnson Samuel ◽  
Richard E. DeVor ◽  
Shiv G. Kapoor
Keyword(s):  
Carbon Nanotube ◽  
Weight Fraction ◽  
Material Model ◽  
Material Behavior ◽  
Compression Tests ◽  
Linear Elastic ◽  
Rate Dependent ◽  
Wide Range ◽  
Parametrization Scheme ◽  
Fraction Length

A continuum-based microstructure-level material model for simulation of polycarbonate carbon nanotube (CNT) composite machining has been developed wherein polycarbonate and CNT phases are modeled separately. A parametrization scheme is developed to characterize the microstructure of composites having different loadings of carbon nanotubes. The Mulliken and Boyce constitutive model [2006, “Mechanics of the Rate Dependent Elastic Plastic Deformation of Glassy Polymers from Low to High Strair Rates,” Int. J. Solids Struct., 43(5), pp. 1331–1356] for polycarbonate has been modified and implemented to capture thermal effects. The CNT phase is modeled as a linear elastic material. Dynamic mechanical analyzer tests are conducted on the polycarbonate phase to capture the changes in material behavior with temperature and strain rate. Compression tests are performed over a wide range of strain rates for model validation. The model predictions for yield stress are seen to be within 10% of the experimental results for all the materials tested. The model is used to study the effect of weight fraction, length, and orientation of CNTs on the mechanical behavior of the composites.

Fatigue Evaluation in Mixing Zones: Comparison of Different Criteria of Fatigue

2008 ◽  
Author(s):  
J. M. Stephan ◽  
C. Gourdin ◽  
J. Angles ◽  
S. Quilici ◽  
L. Jeanfaivre
Keyword(s):  
Fatigue Damage ◽  
Thermal Stresses ◽  
Plastic Material ◽  
Material Behavior ◽  
Damage Evaluation ◽  
Elastic Plastic ◽  
Different Types ◽  
Elastic Plastic Material ◽  
Fatigue Evaluation

The distribution of unsteady temperatures in the wall of the 6" FATHER mixing tee mock-up is calculated for a loading configuration: The results seem realistic even if they are not still very accurate (see paper PVP2005-71592 [11]). On this basis, thermal stresses are evaluated for elastic and elastic-plastic material behavior. Then, different types of fatigue criteria are used to evaluate the fatigue damage. The paper develops a brief description of the criteria, the corresponding fatigue damage evaluation and attempts to explain the differences.

A Continued Evaluation of the Role of Material Hardening Behavior for the NeT TG1 and TG4 Specimens

2014 ◽  
Author(s):  
David J. Dewees ◽  
Phillip E. Prueter ◽  
Seetha Ramudu Kummari
Keyword(s):  
Structural Integrity ◽  
Plastic Material ◽  
Critical Factor ◽  
Material Model ◽  
Standard Test ◽  
Material Behavior ◽  
Weld Residual Stress ◽  
Hardening Models ◽  
Elastic Plastic Material

Modeling of cyclic elastic-plastic material behavior (hardening) has been widely identified as a critical factor in the finite element (FE) simulation of weld residual stresses. The European Network on Neutron Techniques Standardization for Structural Integrity (NeT) Project has provided in recent years both standard test cases for simulation and measurement, as well as comprehensive material characterization. This has allowed the role of hardening in simulation predictions to be isolated and critically evaluated as never before possible. The material testing information is reviewed, and isotropic, nonlinear kinematic and combined hardening models are formulated and tested. Particular emphasis is placed on material model selection for general fitness-for-service assessments, as it relates to the guidance for weld residual stress (WRS) in flaw assessments of in-service equipment in Annex E of the FFS standard, API 579-1/ASME FFS-1.

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