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

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.

## 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

## 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.

## Step by Step Video Tutorial

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

Note: The Designer interface has changed slightly since this video was recorded. The text that follows has been updated to reflect the interface changes.

The full simulation process is detailed in the next section

## 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. In the Home tab of the ribbon, click New Project. The New Project window shows.
2. Type a name for the project.
3. If desired, change the save location and/or project file name by clicking  beside Project File.
4. For Analysis, select Mechanical Dynamic.
5. For Model Type, select 2D Model.
7. For Distance, select mm.
8. Click OK.

#### 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. Expand the Metal tab and double click 'Stainless Steel - stst' to add this to Project Materials
5. Click Done to close the Material Database

### 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

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

#### 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) = 2 and Y (m) = 15
5. Set X (m) = 2 and Y (m) = 17.5
6. Set X (m) = 6.5 and Y (m) = 19
7. Set X (m) = 11 and Y (m) = 19
8. Set X (m) = 11 and Y (m) = 15

Note: At the 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) = 26 and Y (m) = 15
5. Set X (m) = 17 and Y (m) = 15
6. Set X (m) = 17 and Y (m) = 19
7. Set X (m) = 21.5 and Y (m) = 19
8. Set X (m) = 26 and Y (m) = 17.5

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. Select Configuration
2. Set Definitions to Wavelength Based
3. Set Elements Per Wavelength to 15
4. Set Mesh Velocity to Defined
5. Set Mesh Velocity Value to 2350

### Step 6 - Create the load

1. Expand Boundary Conditions and, beside Loads, click +.
2. For Creation Mode, select Geometry Interface.
3. For Geometry, select primitive_3 (rxlt) or click it in the model.
4. For Interfacing Item, select Background (void).

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

With load_1 selected in the Model Tree, do the following in the Properties window:

1. Expand Interface Definition.
2. For Minimum (mm) > X (mm), type 3.
3. For Minimum (mm) > Y (mm), type 15.
4. Set Maximum (mm) > X (mm), type 5.
5. Set Maximum (mm) > Y (mm), type 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

#### 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

### 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

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 Result

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

## 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.