Home / Examples / Stress Analysis [Galileo] / Example 51: Deformation of Viscoelastic Bar

Example 51: Deformation of Viscoelastic Bar

General

The model is a bar made of viscoelastic plastic, polystyrene. It is forced to bend.
The bar is subjected to the temperature change below and over the glass transition temperature.
Unless specified in the list below, the default conditions will be applied.

Obtain this session's project file. (Right-click and choose 'Save link as')
Results will vary depending on Femtet version and the PC environment.

The viscoelastic analysis is a special option.

Analysis Space

Item	Settings
Analysis Space	3D
Model Unit	mm

Analysis Conditions

The bar is subjected to the temperature change below and over the glass transition temperature.

Select [Thermal Load].

Item	Settings
Solver	Stress Analysis [Galileo]
Analysis Type	Static Analysis
Options	Select Thermal Load

The Step/Thermal Load tab is set as follows.

Tab

Setting Item

Settings

Step/Thermal Load

Step Setting

Multi-step Thermal Load Analysis

Time Setting

Set up

Reference temperature

25 [deg]

Step/Reached Temperature Setting

Step	Time [s]	Substeps	Reached Temperature [deg]
1	60	5	25
2	3540	5	25
3	3600	5	25
4	3660	5	120
5	3720	5	120
6	7200	5	120
7	7260	5	120

Options for the Multi-Step Analysis

Save the results of substeps : Select

The reference temperature (non-stress temperature) is 25 [deg]

Time setting is required in the viscoelasticity analysis. Select [Multiple steps] for the step setting and [Set up] for the time setting,
and set the time, substeps, and reached temperature for the step/reached temperature setting.

Each step below consists of 5 substeps.

Step 1 : 60 [s] : The load is increased gradually for 1 min.

Step 2 : 3540 [s] : The load is sustained for almost 1 hour.

Step 3 : 3600 [s] : The load is decreased gradually for 1 min.

Step 4 : 3660 [s] : The temperature is increased to 120 [deg] in 1 min.

Step 5 : 3720 [s] : The load is increased gradually for 1 min.

Step 6 : 7200 [s] : The load is sustained for almost 1 hour.

Step 7 : 7260 [s] : The load is decreased gradually for 1 min.

Save results of substeps is selected by default to output all the results at substeps.

Model

The model is a box solid body with a thickness of 0.4 mm. The material is polystyrene.

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name
0/Solid	Plate	PS

The material properties for PS are set up as follows:

Material Name	Tab	Properties
PS	Elasticity	Material Type: Elastic/Isotropic Temperature Dependency: None Material Property: Young's Modulus: 1.39x109 [Pa] Poisson's Ratio: 0.35
	Viscoelasticity	Defined by: Prony Series [Coefficient Input] Relaxation Component: Shear Only Relaxation Table: Temperature Dependency and Shift Function: WLF Reference Temperature: 113 [deg] C1: 8.86 C2: 101.6
	Coefficient of Linear Thermal Expansion	0X10-6-6 [1/deg]

Boundary Conditions

Boundary Condition Name/Topology

Tab

Boundary Condition Type

Settings

Fix_all/Face

Mechanical

Displacement

Select all X/Y/Z components.

UX=0, UY=0, UZ=0

Pz/Edge

Mechanical

Distributed Edge Load

Select [Set the total load].

X=0, Y=0, Z=-1.0x10-2

Select [Time Dependency] and set [Weight function] as follows.

This setting means the following.

60 [s] : The load is increased gradually for 1 min.

3540 [s] : The load is sustained for almost 1 hour.

3600 [s] : The load is decreased gradually for 1 min.

3720 [s] : The load is increased gradually for 1 min.

7200 [s] : The load is sustained for almost 1 hour.

7260 [s] : The load is decreased gradually for 1 min.

Results

Below are the diagrams of displacements at time 3540 s (about one hour after retaining the bending at 25°C) and

at time 7200 s (about one hour after retaining the bending at 120°C).

The magnitude of displacement is shown.

Displacement at 3540 [s] (Temperature: 25 [deg])

Displacement at 7200 [s] (Temperature:120 [deg])

The deformation is larger at 120 [deg], even though the mechanical load is the same as that of 25 [deg].

The graph below shows the displacement of the plate tip.

The displacement is constant at 25 [deg].

If unloaded, it returns to the original state.

The displacement increases at 120 [deg] even though the load is constant.

If unloaded, it doesn't return to the original state.