Time of Flight Diffraction (TOFD) Inspection of Steel Block with Defect

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Section 1 - What Will You Learn in This Tutorial?

In this tutorial we will learn how to set up a simple 2D model of and we will perform a time of Flight Diffraction (TOFD) inspection of a steel block containing a defect. This model will be created using primitives in Designer.

We will learn:

  • How to set up a 2D model
  • How to assign a time dependent load
  • How to create the 2D geometry using simple geometry shapes
  • How to solve the model to calculate the max acoustic pressure

2D model to simulate a Time of Flight Diffraction (TOFD) inspection of a steel block containing a defect. This model will be created using primitives in Designer.

Section 2- Model Definition

Characteristics of the model:

Model:

Steel block of dimensions 28mm x 15mm

Two probes of dimensions 9mm x 4.096mm with a slope at an 18 degrees angle

Mesh Size:

31μm

Simulation Time:

5e-05 seconds 

Output Results:

-Time history of acoustic pressure at [ 24, 18 ] mm

- Max data array of acoustic pressure

Material Data:

Name Stainless Steel, Generic Rexolite
Code Name stst rxlt
Density 7890 kg.m-3 1060 kg.m-3
Bulk Velocity 5790 ms-1 2340 ms-1
Shear Velocity 3100 ms-1 1100 ms-1

Section 3 - Why This Simulation?

Time of flight diffraction (TOFD) can be used in a variety of applications. It's primary use is rapid weld testing of circumferential and axial weld seams this is also known as perpendicular TOFD scanning. The TOFD method of ultrasonic testing is a sensitive and accurate method of non-destructive testing (NDT).

We will simulate a mechanically generated wave propagating into a steel test block.

Section 4 - Step by Step Video Tutorial

Here is a video tutorial in which you will find all the tutorial in video:

The full simulation process is detailed in the next section 

Section 5 - The Simulation Process:

We will now go through the steps to build this model and perform a simulation

Step 1 - Create a New Project

Before we begin we must create a new project.

  1. Click New Project this opens the New Project window
  2. Choose model name 
  3. Change working units to mm 
  4. Change Model Type to 2D Model
  5. Click ... to choose a directory to save the project
  6. Click OK to create the project.
1.png

Project Settings 

  1. Click Project Settings 
  2. Expand the Frequency of Interest tab (click the toggle box)
  3. Set value to 5e6 Hz

 

Step 2 - Add the Materials from the Material DB

First we will add the materials needed from the material database. We will use Steel in this tutorial.

  1. Click Project Materials to open the Material Database
  2. Expand the Misc tab
  3. Double click 'Rexolite - rxlt' to add this to Project Materials
  4. Copy the same process as step 2 & 3 and add stainless steel (stst) to the project materials
  5. Click Done to close the Material Database
2.png

Step 3 - Create Basic Geometry Shapes

We will make use of the geometric primitives available in Designer. We will use the Rectangle primitive twice.

Primitive 1

  1. Click to add a Rectangle to the workspace
  2. Click primitive_1
  3. Change material to stst
  4. Set End (mm): X (mm) = 28 and Y (mm) = 15
3.png

Note: After making changes to X and Y right click the workspace and select Reset View

Primitive 2

  1. Right click primitive_1 and select Duplicate Selection
  2. Click primitive_2
  3. Change material from steel to void
  4. Set Begin (mm): X (mm) = 13.75 and Y (mm) = 5
  5. Set End (mm): X (mm)  = 14.25 and Y (mm) = 10
mceclip0.png

Primitive 3

  1. Click to add a Polygon to the workspace
  2. Change material to rxlt
  3. Set number of points to 5
  4. Set X (m) = 2e-3 and Y (m) = 15e-3
  5. Set X (m) = 2e-3 and Y (m) = 17.5e-3
  6. Set X (m) = 6.5e-3 and Y (m) = 19e-3
  7. Set X (m) = 11e-3 and Y (m) = 19e-3
  8. Set X (m) = 11e-3 and Y (m) = 15e-3

Note: At the present moment, polygon type of shapes do not support unit transformation to mm, thus input has to be in m unit.

Primitive 4

  1. Click to add a Polygon to the workspace
  2. Change material to rxlt
  3. Set number of points to 5
  4. Set X (m) = 26e-3 and Y (m) = 15e-3
  5. Set X (m) = 17e-3 and Y (m) = 15e-3
  6. Set X (m) = 17e-3 and Y (m) = 19e-3
  7. Set X (m) = 21.5e-3 and Y (m) = 19e-3
  8. Set X (m) = 26e-3 and Y (m) = 17.5e-3

Note: At the present moment, polygon type of shapes do not support unit transformation to mm, thus input has to be in m unit.

Step 4 - Define a Time Function

We will now add a Ricker Wavelet drive function for later use as out loads require a time function be set.

  1. Click '+' to open the Define Input Drive Function window 
  2. Change to Ricker Wavelet 
  3. Set Drive Frequency to 5e6 Hz (same as Frequency of Interest)
  4. Click Insert to close the window. A record called timefunc_1 will be added to the window

Step 5 - Choose the right Mesh Size

We will now change the mesh settings to use 15 elements per wavelength

  1. Expand Model
  2. Expand Mesh
  3. Select Configuration
  4. Set Definitions to Advanced 
  5. Expand Mesh Velocity
  6. Set Mesh Velocity Value to 2350
mesh.png

Step 6 - Create the load

  1.  Click '+' to open the Load Definition window
  2. Change Creation Mode to Geometry Interface 
  3. Change Geometry to primitive_3 (rxlt) and change Interfacing Item to Background (void)
  4. Click Create Load

Upon clicking Create Load a record load_1 will be added to the Model Tree after this you can close the Load Definition window

Edit Load Properties 

  1. Click load_1
  2. Change Load Type to Pressure
  3. Set Driving Function to timefunc_1
  4. Set Minimum (mm): X (mm) = 3 and Y (mm) = 15
  5. Set Maximum (mm): X (mm) = 5 and Y (mm) = 19

 

Step 7 - Define the Boundary Conditions 

  1.  Click Domain Boundaries
  2. Set X minimum to Absorbing
  3. Set X Maximum to Absorbing 
  4. Set Y Minimum to Free
  5. Set Y Maximum to Free

 

Step 8 - Define the Analysis Simulation Time

We will now set the model simulation time to be 1.6e-5 seconds

  1. Click Analysis 
  2. Change Simulation Run Time (s) to 1.6e-5

Step 9 - Define the Output Results

We will now define 2 outputs, a time history of the acoustic pressure on the front of the defect will be recorded and the maximum pressure array will be outputted

Output 1

  1. Click '+' this will create a new output 
  2. Change Output Type to Field Data
  3. Change Array Type to Acoustic pressure
  4. Change Field Type to Maximum
out1.png

 

Output 2

  1. Click '+' this will create a new output 
  2. Change Output Type to Time History 
  3. Change Array Type to Acoustic pressure
  4. Set X = 24 and Y = 18
out2.png

 

Step 10 - Run the Model on the Cloud

At this point the model is completely set up and it can now be run on the cloud.

  1. Click Run on Cloud 
  2. The option to rename your job. This is how it will appear in the storage
  3. Click Estimate 
  4. Click Run

 

Step 11 - Check the Simulation Results

The simulation results will need to be downloaded from the cloud storage in order to analyse the results in the post processor. More experience users may also be able to process Time Histories in Review.

  1. Click Storage this opens the window shown above
  2. Locate the job 
  3. Click Download and click Download all

Choose an appropriate save location when the file explorer pops up and click Select Folder to close the window.

Switch to the Post Processor 

  1. Click this icon to access the Post Processor 

Open Results 

  1. Click File Explorer
  2. Expand the job simulation folder. Open the flxdato file and the flxhst file (double click them)
  3. Click Results Manager 

Plot Time History 

  1. Double click aprs to plot acoustic pressure 
  2. Set plot title to Acoustic Pressure Recorded at Output (optional title)
  3. Set Y-Axis Label to Acoustic Pressure 

 

Plot Data Array (Maximum Pressure)

  1.  Click Reset Viewport and choose Reset All Viewports
  2. Double click apmx to plot the maximum pressure data array

Model Graphics

  1. Click Model Graphics 
  2. Click Surface Plot
  3. Click the workspace and move to rotate the model
 

Section 6 - Try for yourself 

Now that we have introduced you to the tutorial try have a play around with some of the settings, add some other outputs, or use this model as a starting point for your own.

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