Measurement of Cyclic Biaxial Elastoplastic Stresses at Notch Roots

1995 ◽  
Vol 62 (3) ◽  
pp. 646-653 ◽  
Author(s):  
C. H. Yang ◽  
W. N. Sharpe
Keyword(s):  
Constitutive Models ◽  
Measuring System ◽  
Cyclic Plasticity ◽  
Elastoplastic Behavior ◽  
Cyclic Stresses ◽  
Fine Grain ◽  
Notch Geometry ◽  
Cyclic Plasticity Model ◽  
Elastoplastic Constitutive Model ◽  
Good Agreement

A straightforward procedure is demonstrated for measuring local cyclic elastoplastic biaxial stresses at notch roots. First, the biaxial cyclic strains are measured over short gage lengths (150 or 200 micrometers) with a laser-based strain measuring system. Then, cyclic stresses are computed from those measured strains by using an elastoplastic constitutive model. The material selected for this study is HY-80 steel which has a fine grain size and is isotropic. Double-notched specimens were prepared with two different notch geometries: a U-shaped notch with a 4.76 mm radius and a V-shaped notch with a 1.0 mm radius. Two thicknesses, 2.54 and 12.7 mm, were tested for each notch geometry to produce four different amounts of notch constraint. The results of cyclic biaxial strain measurements show good reproducibility. Stress computations based on two different constitutive models were used to compute stresses for the first cycle and a stable cycle. One of the constitutive models is the classical J2flow theory and the other is a two-surface cyclic plasticity model. The results computed using these two models show good agreement with each other. The measured stresses show the effect of constraint on the elastoplastic behavior at notch roots under cyclic loading conditions.

scholarly journals On finite element implementation of cyclic elastoplasticity: theory, coding, and exemplary problems

2021 ◽  
Author(s):  
Cyprian Suchocki
Keyword(s):  
Finite Element ◽  
Kinematic Hardening ◽  
Constitutive Models ◽  
Small Strain ◽  
Cyclic Plasticity ◽  
Isotropic Hardening ◽  
Mapping Algorithm ◽  
Hardening Rule ◽  
Return Mapping ◽  
Cyclic Plasticity Model

AbstractIn this work the finite element (FE) implementation of the small strain cyclic plasticity is discussed. The family of elastoplastic constitutive models is considered which uses the mixed, kinematic-isotropic hardening rule. It is assumed that the kinematic hardening is governed by the Armstrong–Frederick law. The radial return mapping algorithm is utilized to discretize the general form of the constitutive equation. A relation for the consistent elastoplastic tangent operator is derived. To the best of the author’s knowledge, this formula has not been presented in the literature yet. The obtained set of equations can be used to implement the cyclic plasticity models into numerous commercial or non-commercial FE packages. A user subroutine UMAT (User’s MATerial) has been developed in order to implement the cyclic plasticity model by Yoshida into the open-source FE program CalculiX. The coding is included in the Appendix. It can be easily modified to implement any isotropic hardening rule for which the yield stress is a function of the effective plastic strain. The number of the utilized backstress variables can be easily increased as well. Several validation tests which have been performed in order to verify the code’s performance are discussed.

Ratcheting, Wrinkling and Collapse of Tubes Induced by Axial Cycling Under Internal Pressure

2011 ◽  
Author(s):  
Rong Jiao ◽  
Stelios Kyriakides
Keyword(s):  
Cyclic Loading ◽  
Internal Pressure ◽  
Kinematic Hardening ◽  
Cyclic Plasticity ◽  
Combined Loads ◽  
Offshore Pipeline ◽  
Number Of Cycles ◽  
Cyclic Plasticity Model ◽  
Cycles To Failure ◽  
Good Agreement

A buried offshore pipeline is essentially axially constrained by the soil cover. Heating by the passage of hot oil at high pressure can plastically deform it. The deformation involves expansion of the diameter, which for thinner pipes can be accompanied by axisymmetric wrinkling. During a lifetime of 20 or more years, lines experience regular startup and shutdown cycles. This study examines how this cycling affects wrinkling and the hoop expansion of such lines. A set of experiments on super-duplex tubes with D/t of 28.5 was conducted using the following idealized cyclic loading history. A tube is first pressurized and then compressed into the plastic range to a level that initiates wrinkling. It is then cycled under stress control about a compressive mean stress while the pressure is kept constant. The combined loads cause simultaneous ratcheting in the hoop and axial directions as well as a gradual growth of the wrinkles. At some stage the amplitude of the wrinkles starts to grow exponentially with the number of cycles N leading to localization and collapse. The rate of ratcheting and the number of cycles to failure depend on the initial compressive pre-strain, the internal pressure and the stress cycle parameters. The problem is modeled as a shell with initial axisymmetric imperfections. A challenge in the simulations is that the cyclic plasticity model that is used must be capable of capturing correctly the type of biaxial material ratcheting that develops. The Dafalias-Popov two-surface nonlinear kinematic hardening model, enhanced and suitably calibrated is shown to capture the prevalent ratcheting deformations correctly leading to predictions that are in good agreement with the experimental results. The model is then used to evaluate the ratcheting behavior of pipes under thermal-pressure cyclic loading histories seen by buried pipelines.

scholarly journals Cloud Effective Emissivity Retrievals Using Combined Ground-Based Infrared Cloud Measuring Instrument and Ceilometer Observations

2018 ◽  
Vol 10 (12) ◽  
pp. 2033
Author(s):  
Lei Liu ◽  
Ting Zhang ◽  
Yi Wu ◽  
Zhencong Niu ◽  
Qi Wang
Keyword(s):  
Measuring System ◽  
Measuring Instrument ◽  
Effective Emissivity ◽  
Retrieval Method ◽  
Clear Sky ◽  
Inversion Procedure ◽  
The Mean ◽  
And Performance ◽  
Emissivity Measurements ◽  
Good Agreement

In this paper, a new inversion procedure for cloud effective emissivity retrievals using a combined ground-based infrared cloud measuring instrument with ceilometer was developed. A quantitative sensitivity and performance analysis of the proposed method was also provided. It was found that the uncertainty of the derived effective emissivity was mainly associated with errors on the measurement radiance, the simulated radiance of clear sky and blackbody cloudy sky. Furthermore, the retrieval at low effective emissivity was most sensitive to the simulated clear sky radiances, whereas the blackbody cloudy sky radiance was the prevailing source of uncertainty at high emissivity. This newly proposed procedure was applied to the measurement taken in the CMA Beijing Observatory Station from November 2011 to June 2012 by the whole-sky infrared cloud-measuring system (WSIRCMS) and CYY-2B ceilometer. The cloud effective emissivity measurements were in good agreement with that of the MODIS/AQUA MYD06 Collection 6 (C6) cloud products. The mean difference between them was 0.03, with a linear correlation coefficient of 0.71. The results demonstrate that the retrieval method is robust and reliable.

Development and verification of a numerical model for the analysis of geosynthetic-reinforced soil segmental walls under working stress conditions

2005 ◽  
Vol 42 (4) ◽  
pp. 1066-1085 ◽  
Author(s):  
Kianoosh Hatami ◽  
Richard J Bathurst
Keyword(s):  
Numerical Model ◽  
Constitutive Models ◽  
Reinforced Soil ◽  
Stress Conditions ◽  
Soil Reinforcement ◽  
Lagrangian Analysis ◽  
Elastic Plastic ◽  
Geosynthetic Reinforced Soil ◽  
Working Stress ◽  
Good Agreement

The paper describes a numerical model that was developed to simulate the response of three instrumented, full-scale, geosynthetic-reinforced soil walls under working stress conditions. The walls were constructed with a fascia column of solid modular concrete units and clean, uniform sand backfill on a rigid foundation. The soil reinforcement comprised different arrangements of a weak biaxial polypropylene geogrid reinforcement material. The properties of backfill material, the method of construction, the wall geometry, and the boundary conditions were otherwise nominally the same for each structure. The performance of the test walls up to the end of construction was simulated with the finite-difference-based Fast Lagrangian Analysis of Continua (FLAC) program. The paper describes FLAC program implementation, material properties, constitutive models for component materials, and predicted results for the model walls. The results predicted with the use of nonlinear elastic-plastic models for the backfill soil and reinforcement layers are shown to be in good agreement with measured toe boundary forces, vertical foundation pressures, facing displacements, connection loads, and reinforcement strains. Numerical results using a linear elastic-plastic model for the soil also gave good agreement with measured wall displacements and boundary toe forces but gave a poorer prediction of the distribution of strain in the reinforcement layers.Key words: numerical modelling, retaining walls, reinforced soil, geosynthetics, FLAC.

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