A finite element study of the pressuremeter test in sand using a nonlinear elastic plastic model

1993 ◽  
Vol 30 (2) ◽  
pp. 348-362 ◽  
Author(s):  
Martin Fahey ◽  
John P. Carter
Keyword(s):  
Finite Element ◽  
Shear Modulus ◽  
Hyperbolic Model ◽  
Type Model ◽  
Model Parameters ◽  
Nonlinear Behaviour ◽  
Stress Strain ◽  
Pressuremeter Test ◽  
Strain Behaviour ◽  
Highly Nonlinear

The stress–strain behaviour of sands is highly nonlinear, even at stresses well below the peak strength of the sand. The hyperbolic model is a reasonable conceptual model for representing the stress–strain behaviour of sand, but some empirical curve fitting is required to obtain a more realistic model for calculation purposes. This can readily be performed for reconstituted samples of sand using laboratory tests. Recent evidence shows that the stiffness of natural sands is often much greater than that of the same sand when reconstituted at the same density and stress state in the laboratory, and it is therefore necessary to use in situ testing methods to determine the stress–strain behaviour of such sands. In this paper, the finite element method is used to simulate pressuremeter tests in a soil modelled using a hyperbolic-type model. It concentrates on the behaviour in unload-reload loops, which are often included in pressuremeter tests to measure shear modulus. The effect on the whole unload-reload loop of varying some of the model parameters is examined. The results are compared with a high-quality pressuremeter test in sand. It is concluded that, though the results to date are encouraging, some further experimental work is required to verify some of the features of the model. Key words : pressuremeter test, hyperbolic model, nonlinear behaviour, initial shear modulus, sand behaviour.

scholarly journals A double-layer Boussinesq-type model for highly nonlinear and dispersive waves

2009 ◽  
Vol 465 (2108) ◽  
pp. 2319-2346 ◽  
Author(s):  
F. Chazel ◽  
M. Benoit ◽  
A. Ern ◽  
S. Piperno
Keyword(s):  
Double Layer ◽  
Deep Water ◽  
Type Model ◽  
Nonlinear Behaviour ◽  
Approximate Inverse ◽  
Dispersive Waves ◽  
Final Model ◽  
Water Value ◽  
Highly Nonlinear ◽  
Model Derivation

We derive and analyse, in the framework of the mild-slope approximation, a new double-layer Boussinesq-type model that is linearly and nonlinearly accurate up to deep water. Assuming the flow to be irrotational, we formulate the problem in terms of the velocity potential, thereby lowering the number of unknowns. The model derivation combines two approaches, namely the method proposed by Agnon et al. ( Agnon et al. 1999 J. Fluid Mech. 399 , 319–333) and enhanced by Madsen et al. ( Madsen et al. 2003 Proc. R. Soc. Lond. A 459 , 1075–1104), which consists of constructing infinite-series Taylor solutions to the Laplace equation, to truncate them at a finite order and to use Padé approximants, and the double-layer approach of Lynett & Liu ( Lynett & Liu 2004 a Proc. R. Soc. Lond. A 460 , 2637–2669), which allows lowering the order of derivatives. We formulate the model in terms of a static Dirichlet–Neumann operator translated from the free surface to the still-water level, and we derive an approximate inverse of this operator that can be built once and for all. The final model consists of only four equations both in one and two horizontal dimensions, and includes only second-order derivatives, which is a major improvement in comparison with so-called high-order Boussinesq models. A linear analysis of the model is performed, and its properties are optimized using a free parameter determining the position of the interface between the two layers. Excellent dispersion and shoaling properties are obtained, allowing the model to be applied up to the deep-water value k h =10. Finally, numerical simulations are performed to quantify the nonlinear behaviour of the model, and the results exhibit a nonlinear range of validity reaching at least k h =3π.

Polycrystalline plasticity and the evolution of crystallographic texture in FCC metals

1992 ◽  
Vol 341 (1662) ◽  
pp. 443-477 ◽  
Keyword(s):  
Finite Element ◽  
Crystallographic Texture ◽  
Single Phase ◽  
Type Model ◽  
Strain Response ◽  
Stress Strain ◽  
Fcc Metals ◽  
First Order ◽  
Finite Element Calculations ◽  
Simple Compression

A Taylor-type model for large deformation polycrystalline plasticity is formulated and evaluated by comparing the predictions for the evolution of crystallographic texture and the stress-strain response in simple compression and tension, plane strain compression, and simple shear of initially ‘isotropic’ OFHC copper against ( a ) corresponding experiments, and ( b ) finite element simulations of these experiments using a multitude of single crystals with accounting for the satisfaction of both compatibility and equilibrium. Our experiments and calculations show that the Taylor-type model is in reasonable first-order agreement with the experiments for the evolution of texture and the overall stress-strain response of single-phase copper. The results of the finite element calculations are in much better agreement with experiments, but at a substantially higher computational expense.

Shear strength and stress—strain behaviour of Athabasca oil sand at elevated temperatures and pressures

1987 ◽  
Vol 24 (1) ◽  
pp. 1-10 ◽  
Author(s):  
J. G. Agar ◽  
N. R. Morgenstern ◽  
J. D. Scott
Keyword(s):  
Shear Strength ◽  
Oil Sands ◽  
Elevated Temperatures ◽  
Triaxial Compression ◽  
Substantial Reduction ◽  
Hyperbolic Model ◽  
Oil Sand ◽  
Hydrocarbon Gases ◽  
Stress Strain ◽  
Strain Behaviour

The results of a series of triaxial compression tests on undisturbed samples of Athabasca oil sand at elevated temperatures ranging from 20 to 200 °C are summarized. The material tested had experienced gradual unloading and depressurization as a result of erosion in the Saline Creek valley near Fort McMurray. More deeply buried oil sands are known to contain much higher concentrations of dissolved hydrocarbon gases in the pore fluids. The measured shear strength of Athabasca oil sand did not change significantly as a result of the increased temperatures that were applied. The strength of Athabasca oil sand (at 20–200 °C) was found to be greater than comparable shear strengths reported for dense Ottawa sand (at 20 °C). Although heating to 200 °C had little effect on shear strength, it is recognized that pore pressure generation during undrained heating may cause substantial reduction of the available shearing resistance, particularly in gas-rich oil sands. The experimental data were used to investigate the influence of such factors as stress path dependency, microfabric disturbance, and heating to elevated temperatures on the shear strength and stress–strain behaviour of oil sand. Curve fitting of the test data suggests that the hyperbolic model is a useful empirical technique for stress—deformation analyses in oil sands. Hyperbolic stress—strain parameters derived from the experimental results for Athabasca oil sand are presented. Key words: oil sand, Athabasca oil sand, tar sand, shear strength, stress, strain, deformation, heating, high temperature, elevated temperatures, high pressure, elevated pressure, thermal properties, drained heating, undrained heating, triaxial compression testing.

A Revised Anand Constitutive Model for Lead Free Solder That Includes Aging Effects

2013 ◽  
Author(s):  
Mohammad Motalab ◽  
Munshi Basit ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Constitutive Equations ◽  
Mechanical Tests ◽  
The Other ◽  
Lead Free ◽  
Model Parameters ◽  
Aging Effects ◽  
Stress Strain ◽  
Profile Matching

Traditional finite element based predictions for solder joint reliability during thermal cycling accelerated life testing are based on solder constitutive equations (e.g. Anand viscoplastic model) and failure models (e.g. energy dissipation per cycle model) that do not evolve with material aging. Thus, there will be significant errors in the calculations with lead free SAC alloys that illustrate dramatic aging phenomena. In this study, we have developed a revised set of Anand viscoplastic stress-strain relations for solder that include material parameters that evolve with the thermal history of the solder material. The effects of aging on the nine Anand model parameters have been examined by performing stress-strain tests on SAC305 samples that were aged for various durations (0–6 months) at temperature of 100 C. The stress-strain data were measured at three strain rates (.001, .0001, and .00001 1/sec) and five temperatures (25, 50, 75, 100, and 125 C). The mechanical tests have been performed using both water quenched (WQ) and reflowed (RF) samples (two unique specimen microstructures). In the case of the water quenched samples, there is rapid microstructural transitioning during the brief time that occurs between placing molten solder into the glass tubes and immersing the tubes in water bath. On the other hand, the reflowed samples are first cooled by water quenching, and then sent through a reflow oven to re-melt the solder in the tubes and subject them to a desired temperature profile matching that used in PCB assembly. As expected, the observed mechanical properties of water quenched samples were better (higher in magnitude) than the corresponding mechanical properties of the reflowed samples. Although the differences in elastic modulus between the water quenched and reflowed samples are small, significant differences are present for the yield and ultimate tensile stresses (for each aging condition). For both the water quenched and reflowed specimens, significant degradation of the mechanical properties has been observed with aging. Using the measured stress-strain and creep data, mathematical expressions have been developed for the evolution of the Anand model parameter with aging time. Our results show that 2 of the 9 constants remain essentially constant during aging, while the other 7 show large changes (30–70%) with up to 6 months of aging. The revised Anand constitutive equations for solder with aging effects have also been incorporated into commercial finite element codes (ANSYS and ABAQUS).

Elastic viscoplastic modelling of the time-dependent stress-strain behaviour of soils

1999 ◽  
Vol 36 (4) ◽  
pp. 736-745 ◽  
Author(s):  
Jian-Hua Yin ◽  
James Graham
Keyword(s):  
Strain Rate ◽  
Creep Test ◽  
Triaxial Compression ◽  
Constant Strain Rate ◽  
Time Dependent ◽  
Model Parameters ◽  
Stress Strain ◽  
Equivalent Time ◽  
Strain Behaviour ◽  
Modified Cam Clay

This paper presents a new framework for elastic viscoplastic (EVP) constitutive modelling. In developing the model, a general one-dimensional elastic viscoplastic (1D EVP) relationship is first derived for isotropic stressing conditions using an "equivalent-time" concept. This 1D EVP model is then generalized into a three-dimensional EVP model based on Modified Cam-Clay and viscoplasticity. Fitting functions are proposed for fitting data when model parameters are being determined. Using these functions, a specific EVP model is developed which describes the time-dependent stress-strain behaviour of soils under triaxial stress states. This model has been calibrated using data from a densely compacted sand-bentonite mixture. The calibrated model is used to compute time-dependent (or strain rate dependent) stress-strain curves from a multistage shear creep test and a step-changed, constant strain rate undrained triaxial compression test. Predictions from the EVP model are in general agreement with measured values. It is demonstrated that the model can simulate accelerating creep when deviator stresses are close to the shear strength envelope in a q creep test. It can also model the behaviour in unloading-reloading and relaxation. Limitations and possible improvements are also indicated.Key words: equivalent time, stress-strain, time dependent, elastic, viscoplastic, triaxial.

scholarly journals Finite Element Modelling of Cold Formed Stainless Steel Columns

10.14311/722 ◽  
2005 ◽  
Vol 45 (3) ◽  
Author(s):  
M. Macdonald ◽  
J. Rhodes
Keyword(s):  
Finite Element ◽  
Stainless Steel ◽  
Load Capacity ◽  
304 Stainless Steel ◽  
Channel Cross Section ◽  
Stress Strain ◽  
Steel Columns ◽  
Strain Behaviour ◽  
Type 304 ◽  
Type 304 Stainless Steel

This paper describes the results obtained from a finite element investigation into the load capacity of column members of lipped channel cross-section, cold formed from Type 304 stainless steel, subjected to concentric and eccentric compression loading. The main aims of this investigation were to determine the effects which the non-linearity of the stress-strain behaviour of the material would have on the column behaviour under concentric or eccentric loading. Stress-strain curves derived from tests and design codes are incorporated into non-linear finite element analyses of eccentrically loaded columns and the results obtained are compared with those obtained on the basis of experiments on stainless steel channel columns with the same properties and dimensions. Comparisons of the finite element results and the test results are also made with existing design specifications and conclusions are drawn on the basis of the comparisons. 

scholarly journals Non-linear finite element analysis of the dynamics of a slender cable stayed tower

2018 ◽  
Vol 148 ◽  
pp. 03001
Author(s):  
Eliot Pezo ◽  
Paulo Gonçalves ◽  
Deane Roehl
Keyword(s):  
Finite Element ◽  
Structural Model ◽  
Design Stage ◽  
Nonlinear Behaviour ◽  
The Finite Element Method ◽  
Element Analysis ◽  
Highly Nonlinear ◽  
Load Carrying ◽  
Post Buckling ◽  
Interactive Buckling

The aim of the present work is to investigate the static and dynamic nonlinear behaviour of a cable-stayed tower. A continuous structural model of a slender tower is discretized by the finite element method. First the buckling and post-buckling behaviour of the tower under axial load is explored, in order to understand the influence of the cable stiffness and lateral restrain on the load carrying capacity of the tower. Then, the linear vibration modes and frequencies are obtained. Due to the inherent symmetries of the tower, coincident buckling loads and vibration frequencies are obtained. This may lead to interactive buckling and internal resonance, increasing the effect of the geometric nonlinearities on the response. The results show that the tower exhibits a highly nonlinear response, which must be considered with care in the design stage.

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