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# a8-quasi-static-ia

By Bill Ruiz,2014-10-05 07:13
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a8-quasi-static-ia

Quasi-Static and Import Analysis

Interactive Version

Question W81: What analysis procedure is used in this model?

Answer: The analysis procedure is a natural frequency extraction.

Question W82: In Abaqus a distinction is made between linear perturbation

analysis steps and general analysis steps. What type of

procedure is the analysis procedure in this model? Answer: Frequency extraction is a linear perturbation procedure.

Question W83: In an analysis with more than one step in the same model,

what influence does the result of a linear perturbation step

have on the base state of the model for the following analysis

step?

Answer: None. Only general analysis steps change the base state of the

model.

Question W84: What effect will an increase in friction have on the solution? Answer: An increased friction coefficient will increase the critical shear

stress at which sliding of the blank begins. Thus, the crit

material will be stretched more, causing further thinning of the

material and increasing the stresses.

? Dassault Systèmes, 2008 Introduction to Abaqus/Standard and Abaqus/Explicit

WA8.2

Question W85: When entering plasticity data into the material model, what

are the stress and strain measures that Abaqus uses? Answer: Abaqus uses true (Cauchy) stress and log strain.

Question W86: What effects would a higher damping coefficient have? Answer: A higher damping coefficient would reduce the stable time

increment. In general, damping should be chosen such that

high frequency oscillations are smoothed or eliminated with

minimal effect on the stable time increment. Figure WA81

shows a plot of the kinetic energy with and without damping.

Note the high frequency oscillations in the analysis without

damping.

Figure WA81. Kinetic energy with and without damping

Question W87: What is the slope of the curve at the beginning and end, and

why is this important?

Answer: The slope of the amplitude curve at the beginning and end of

the step is zero. This is important because it prevents

discontinuities in the punch displacement, which lead to

oscillations in an Abaqus/Explicit analysis.

? Dassault Systèmes, 2008 Introduction to Abaqus/Standard and Abaqus/Explicit

WA8.3

Question W88: How would the results change if a linear amplitude definition

Answer: With a linear amplitude definition the displacement of the

punch will be applied suddenly at the beginning of the step

and stopped suddenly at the end of the step, causing

oscillations in the solution.

A linear amplitude definition results in large spikes in the

kinetic energy, especially at the beginning of the step. As a

result, the kinetic energy may be large compared to the

internal energy and the early solution may not be quasi-static.

The preferred approach is to move the punch as smoothly as

possible. Figure WA82 compares the kinetic energy history

when a linear amplitude definition is used and when the

smooth step amplitude definition is used.

Figure WA82. Kinetic energy plot with and without SMOOTH STEP

Question W89: How do you determine if an analysis that includes mass

scaling produces acceptable results?

Answer: The kinetic energy should be a small fraction of the internal

energy.

As the kinetic energy increases, inertia effects have to be

considered and the solution is no longer quasi-static.

? Dassault Systèmes, 2008 Introduction to Abaqus/Standard and Abaqus/Explicit

WA8.4

Figure WA83 shows the internal and kinetic energy for mass

scaling factors of 10 (used in our simulation), 100, and 900,

which correspond to a solution speedup of 10, 10, and 30,

respectively.

Figure WA83. Energies with different mass scaling

Question W810: How does mass scaling affect the solution time? Answer: The stable time increment is calculated according to

e ？，L，(；;tmin,stable，(cd！；

ewhere L is a characteristic element length and c is the d

dilatational wave speed. An increase in density decreases c, d

which in turn increases t. stable

Question W811: What elements are used to model the blank, and does this

element type have an hourglass deformation mode? Answer: The analysis uses SAX1 elements. These elements have no

hourglass modes. Consequently, hourglassing is not of

concern in the analysis.

? Dassault Systèmes, 2008 Introduction to Abaqus/Standard and Abaqus/Explicit

WA8.5

Question W812: Why is it advantageous to choose Abaqus/Standard for the

springback analysis?

Answer: A true static procedure is the preferred approach for modeling

springback. The imported model will not be in static

equilibrium at the beginning of the step. Thus,

Abaqus/Standard applies a set of artificial internal stresses to

the imported model state and then gradually removes these

stresses. This leads to the springback deformation. In

Abaqus/Explicit the removal of the contact between the blank