The simSUNDT software is based on a previous developed program (SUNDT). The latest version has been customized in order to generate realistic synthetic data (including a grain noise model), compatible with a number of off-line analysis software. The software consists of a Windows®-based preprocessor and postprocessor together with a mathematical kernel (UTDefect), dealing with the actual mathematical modeling. The model employs various integral transforms and integral equation and enables simulations of the entire ultrasonic testing situation. The model is completely three-dimensional though the simulated component is two-dimensional, bounded by the scanning surface and a planar back surface as an option. It is of great importance that inspection methods that are applied are proper validated and that their capability of detection of cracks and defects are quantified. In order to achieve this, statistical methods such as Probability of Detection (POD) often are applied, with the ambition to estimate the detectability as a function of defect size. Despite the fact that the proposed procedure with the utilization of test pieces is very expensive, it also tends to introduce a number of possible misalignments between the actual NDT situation that is to be performed and the proposed experimental simulation. The presentation will describe the developed model that will enable simulation of a phased array NDT inspection and the ambition to use this simulation software to generate POD information. The paper also includes the most recent developments of the model including some initial experimental validation of the phased array probe model. © 2010 American Institute of Physics

Persson, Gert

Wirdelius, Håkan

Persson, Gert,

Wirdelius, Håkan,

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Recent survey and application of the simSUNDT software [Elektronisk resurs]

The simSUNDT software is based on a previous developed program (SUNDT). The latest version has been customized in order to generate realistic synthetic data (including a grain noise model), compatible with a number of off-line analysis software. The software consists of a Windows\uae-based preprocessor and postprocessor together with a mathematical kernel (UTDefect), dealing with the actual mathematical modeling. The model employs various integral transforms and integral equation and enables simulations of the entire ultrasonic testing situation. The model is completely three-dimensional though the simulated component is two-dimensional, bounded by the scanning surface and a planar back surface as an option. It is of great importance that inspection methods that are applied are proper validated and that their capability of detection of cracks and defects are quantified. In order to achieve this, statistical methods such as Probability of Detection (POD) often are applied, with the ambition to estimate the detectability as a function of defect size. Despite the fact that the proposed procedure with the utilization of test pieces is very expensive, it also tends to introduce a number of possible misalignments between the actual NDT situation that is to be performed and the proposed experimental simulation. The presentation will describe the developed model that will enable simulation of a phased array NDT inspection and the ambition to use this simulation software to generate POD information. The paper also includes the most recent developments of the model including some initial experimental validation of the phased array probe model. \ua9 2010 American Institute of Physics

Wirdelius, H\ue5kan

Chalmers Research

Recent survey and application of the simSUNDT software

Chalmers Publication Library

 
 
 
 
 
 
 
 
 
 
 
RECENT SURVEY AND APPLICATION OF THE simSUNDT 
SOFTWARE 
 
 
G. Persson and H. Wirdelius 
 
Department of Materials and Manufacturing Technology, 
Chalmers University of Technology, 412 96 Gothenburg, Sweden 
 
 
ABSTRACT.  The simSUNDT software is based on a previous developed program (SUNDT). The 
latest version has been customized in order to generate realistic synthetic data (including a grain noise 
model), compatible with a number of off-line analysis software. The software consists of a 
Windows®-based preprocessor and postprocessor together with a mathematical kernel (UTDefect), 
dealing with the actual mathematical modeling. The model employs various integral transforms and 
integral equation and enables simulations of the entire ultrasonic testing situation. The model is 
completely three-dimensional though the simulated component is two-dimensional, bounded by the 
scanning surface and a planar back surface as an option.  It is of great importance that inspection 
methods that are applied are proper validated and that their capability of detection of cracks and 
defects are quantified. In order to achieve this, statistical methods such as Probability of Detection 
(POD) often are applied, with the ambition to estimate the detectability as a function of defect size. 
Despite the fact that the proposed procedure with the utilization of test pieces is very expensive, it also 
tends to introduce a number of possible misalignments between the actual NDT situation that is to be 
performed and the proposed experimental simulation.  The presentation will describe the developed 
model that will enable simulation of a phased array NDT inspection and the ambition to use this 
simulation software to generate POD information. The paper also includes the most recent 
developments of the model including some initial experimental validation of the phased array probe 
model. 
 
Keywords: Ultrasonic, Simulation, Backscattered Noise, Phased Array Model 
PACS:  43.20.Fn, 43.35.Zc, 46.40.Cd. 
 
INTRODUCTION 
 
 Demands from mainly the Nuclear Power Industry on reliability of NDE/NDT 
procedures and methods have encouraged the development of simulation tools of NDT. 
Regulations usually demands inspection methods that have been qualified, and simulation 
can be used as an alternative and a complement to the experimental work that are acquired 
to qualify the procedures. The qualification of inspection systems includes the reliability to 
detect, locate, characterize and accurately determine the size of defects that may occur in 
the specific type of component. 
 
2125
 
 
The simSUNDT is such simulation software that originally was developed in order 
to generate synthetic data compatible with a number of off-line analysis software [1]. 
 
simSUNDT 
 
 The simSUNDT program is a Windows®-based preprocessor and postprocessor, 
see Fig. 1, together with a mathematical kernel (UTDefect, [2-6]) dealing with the actual 
mathematical modeling. The UTDefect computer code has been developed at the Dept. of 
Mechanics at Chalmers University of Technology and has been experimentally validated 
and verified [3-5]. The mathematical kernel employs various integral transforms and 
integral equation techniques to model probes and the scattering by defects, providing 
numerically exact solutions. The software simulates the whole testing procedure with the 
contact probes (of arbitrary type, angle and size) acting in pulse-echo or tandem inspection 
situations. The simulated test piece is at the present state restricted to be of a homogeneous 
and isotropic material. The model is completely three dimensional though the component 
is two dimensional (infinite plate with finite or infinite thickness) bounded by the scanning 
surface where one or two probes are scanning the object within a rectangular mesh. It is 
also possible to include a planar back surface, which for the strip-like crack may be tilted, 
but is otherwise assumed parallel to the scanning surface.  
Three crack-like defects are included in the software: rectangular crack (lack of 
fusion), circular crack (lack of fusion) and strip-like crack (fatigue crack). Both the 
rectangular and the strip-like crack include the possibility to model roughness on the crack 
surfaces. The circular crack can also be modeled as partly closed, with the degree of 
closure related to the crack surface conditions (roughness) and the background pressure.  
The four included volumetric defects are: a spherical cavity (pore), a spherical inclusion 
made of an isotropic material differing from the surrounding medium (slag), a spheroid 
cavity (pore), and a cylindrical cavity. Either the cylindrical cavity or the circular crack can 
be used as reference in the simulations, i.e. modeling calibration with a side drilled hole 
(SDH) or a flat bottom hole (FBH). 
 
 
  
 
 
FIGURE 1.  The preprocessor (left) and postprocessor (right) in the simSUNDT software. 
 
 
2126
 
 
THE GRAIN NOISE MODEL 
 
 If realistic data are to be used in the process of generating synthetic POD there is a 
need for a model of the weld and the corresponding backscattered grain noise that is 
superposed to the defect signal that correlates better to a real inspection situation.  A 
welding procedure does introduce different material properties in terms of anisotropy and 
grain size enlargement. Methods for calculating the backscattering of ultrasound due to 
grain boundaries have been developed during the last decade (e.g. see [7, 8]). In order to 
simulate this phenomenon a rather simple model is deduced. It consists of modeling grain 
noise by a random distribution of elastic spherical inclusions in a weld geometry where the 
radius of the inclusions are calculated from a one dimensional model relating welding 
conditions and grain size in weld heat-affected zone (HAZ). In Fig. 2 the weld geometry 
parameters are shown together with the Heat-Affected Zone (HAZ). No multiple scattering 
effects are considered in the noise signal but only a superposition of direct scattering from 
each defect. 
 In the heat-affected zone the grain sizes vary with the distance from the fusion line. If 
we neglect size and shape of heat source, temperature dependence of heat conductivity and 
specific heat, thermal loss from material surface and latent heat of fusion, the heat source 
can be modeled as a moving line heat source [9].  
 When calculating the grain size, the HAZ is divided into n parts with thickness bn as in 
Fig. 2. The fusion line is approximated by the boundary of the weld.  
 In order to reduce computational time it is necessary to limit the extension of the grain 
noise model. Grains outside the heat effect zone are thus not included. The number of 
inclusions must therefore be limited to avoid a non-physical discontinuity in the object 
(grains/no grains). On the other hand the number of defects used should ensure that the 
central limit theorem is satisfied. To validate this, a control volume was investigated in 
order to evaluate a sufficient (volume fraction) number of defects, called the level of 
saturation dispersion. The inclusions have the same density as the surrounding material but 
were provided with slightly deviating wave speeds, corresponding to 20% increase in 
stiffness.  
 Figure 3 shows a signal response that is almost linear with the number of defects for 
the case where the boundary of the volume is included. For the case where only the defects 
within the volume are included, that is where the signal from boundaries is excluded, we 
evidently get saturation in the signal response. 
 
 
 
FIGURE 2.  The weld geometry and HAZ. 
 
  
b1 
b2 
b3 
bn 
t1 
t2 
m = 1 
m = 2 
xhaz 
z 
x 
2127
 
 
 
FIGURE 3. Grain noise amplitude as function of number of inclusions (the ◊ marked values are rms-values 
based on signals from the whole volume while  marked values are from within the volume). 
 
 Figure 4 shows the distribution of grain size in the weld and HAZ as a function of the 
x-coordinate. Each dot represents a spherical inclusion at a specific x-coordinate from the 
veldcenter, and with a particular radius. According to the evaluated number of inclusions 
per volume they could be distributed without taking into account to their individual size 
i.e. constant number per volume as shown in the left figure. However, in the computations 
we have chosen to let the inclusions have a constant fraction of the modeled volume in 
each sub region [10] as shown in the right figure. 
 The number of inclusions in the outer sub region is therefore defined by the level of 
saturation of dispersion without producing the unwanted phenomena we previously 
discussed. The number of inclusions in the other sub regions is provided by a constant 
fraction in each sub volumes.  
 Figure 5 shows the grain positions projected into the xy-plane. Each dot only represents 
the specific position in the xy-plane, the radius of spherical inclusion is not shown. The 
 
 
FIGURE 4.  The distribution of grain size in the weld and HAZ as a function of the x-coordinate (Fig. 2). 
Left with the condition of constant number per volume and right according to constant volume fraction. 
 
x-coord from weldcenter (mm) x-coord from weldcenter (mm) 
R
ad
iu
s o
f i
nc
lu
si
on
s (
m
m
) 
R
ad
iu
s o
f i
nc
lu
si
on
s (
m
m
) 
Number of inclusions
A
m
pl
itu
de
 
2128
 
 
  
 
FIGURE 5.  Grain position in the xy-plane. Left with the condition of constant number per volume and right  
according to constant volume fraction. 
 
decrease of grain size as function of the x-coordinate becomes obvious in the right figure 
since the numbers of grains that need to fulfill the condition of constant volume fraction 
are increased with the x-coordinate.  
 
PHASED ARRAY PROBE 
 
 The recent development also includes a mathematical model of a phased array 
probe and the implementation of it into the simSUNDT software. The phased array probe 
has been treated in the same way as previously was done for the conventional contact 
probe (see Fig. 6).  
 Each element is then represented by the boundary conditions that generate a plane 
wave, at a certain angle, in the far field. These boundary conditions (i.e. the pressure on the 
surface under the element) are then translated into the main coordinate system and after 
superposition they built up a phased array wave front (constructive phase interference) 
with prescribed nominal angle. Alteration of prescribed angle of each element then enables 
also enables a focusing effect. 
 
 
 
 
FIGURE 6.  Geometry and parameters that defines the phased array probe (left), boundary conditions on the 
surface and far field plane wave (right). 
y-
co
or
di
na
te
 (m
m
) 
y-
co
or
di
na
te
 (m
m
) 
x-coordinate (mm) x-coordinate (mm) 
2129
 
 
EXPERIMENTAL RESULTS 
 
 Within this year’s benchmark an experimental study was provided that also 
included experimental work conducted with a well defined phased array probe on a planar 
block containing side-drilled holes (SDH), flat-bottom holes (FBH) and some vertical 
planar back wall breaking flaws (SBC) of different heights and extensions. The 
experimental data for these studies were conducted and generously provided by CEA in 
France.  
 Data that represents experimental signal responses, from defects that simSUNDT 
(version 1.2) is able to simulate, are provided in Table 1. Only 20 of the 48 elements in the 
linear phased array probe were activated and specification of used delay laws for these was 
provided as information in the documentation. The delay laws were calculated to obtain a 
45° longitudinal wave without any focusing effect in ferritic steel but the material in used 
test piece was specified as stainless steel (cL=5750 m/s). Based upon an ad hoc 
assumptions of the wave speed in ferritic steel (cL≈5900 m/s) and that no focusing effect 
would occur,  43.5° was used as the nominal angle throughout most simulations.  
 Due to the fact that both longitudinal and transverse portions of reflected energy 
were provided as information it rather soon became obvious that modeled couplant 
conditions was less viscous than in previous validations (water instead of ultrasonic gel, 
see ref. [5]) which later on was confirmed by CEA. The simulation results when using 20 
small elements (probes) to model the phased array probe are found in Table 2. The slots 
(width of 40 mm) in the test piece are modeled by a surface breaking (2 dimensional) 
crack in the simulations. As can be deduced from the results the volumetric defects (SDH 
and FBH) correlates very well to the experimental signal responses but this is not the case 
when it comes to the surface breaking crack. The explanation to this is probably that an 
infinite mathematical surface is a poor model of a more or less volumetric slot with limited 
dimensions though the defect model previously was verified using fatigue cracks (ref. [3-
5]). Another explanation could be that the slots are situated at different depths than the 
reference defect and that the described procedure above could produce some kind of 
focusing effect.    
 
TABLE 1.  Experimental data (signal response in dB) provided in the 2009 Benchmark.  The 2 mm  
(diameter) side-drilled hole was used as reference reflector.  
 SDH FBH SBC  
1 mm 1.5 mm 2 mm 3 mm 2 mm 5 mm 
L 
direct echo 
-2.6 -1.3 0 (ref) 2.8 -10.5 -3.6 L 
corner echo 
T 
direct echo 
-16.5 -16.3 -14.8  -16.2 -7.3 T 
corner echo 
     -23.9 -21.7 TL 
corner echo 
 
TABLE 2.  Deviations (20log[Asimu./ Aexp.]) from the experimental results (found in Table 1) when 
simulating the phased array with 20 elements.  
 SDH FBH SBC  
1 mm 1.5 mm 2 mm 3 mm 2 mm 5 mm 
L 
direct echo 
-0.4 -0.1 0 (ref) 1.8 9.6 9.2 L 
corner echo 
T 
direct echo 
-3.6 -1.5 -1.7  -2.4 -11.3 T 
corner echo 
     12.7 11.8 TL 
corner echo 
 
2130
 
 
 
TABLE 3.  Deviations (20log[Asimu./ Aexp.]) from the experimental results (found in Table 1) when 
simulating the phased array with one single large element.  
 SDH FBH SBC  
1 mm 1.5 mm 2 mm 3 mm 2 mm 5 mm 
L 
direct echo 
-0.2 0.1 0 (ref) 2.8 6.6 6.1 L 
corner echo 
T 
direct echo 
8.9 11.0 10.5  6.5 -0.1 T 
corner echo 
     1.2 -0.5 TL 
corner echo 
 
TABLE 4.  Deviations (20log[Asimu./ Aexp.]) from the experimental results (found in Table 1) when 
simulating the phased array with 20 elements generating a pulse with an angle of 47.5°.  
 SDH FBH SBC  
1 mm 1.5 mm 2 mm 3 mm 2 mm 5 mm 
L 
direct echo 
-0.3 0 0 (ref) 2.0 8.2 9.7 L 
corner echo 
T 
direct echo 
-1.7 0.1 0  0.2 -9.7 T 
corner echo 
     8.6 9.4 TL 
corner echo 
 
The results found in Table 3 are from simulations using only one single element 
which corresponds to modeling the phased array as a conventional ultrasonic contact 
probe. The received longitudinal contribution to the signal response still agrees fairly well 
while the transversal part deviates from the experimental data. This could be explained by 
the fact that the reflectors are situated less than one near field length from the probe. 
Interesting though is that the correlation between the SBC and the slot are improving by 
reducing the number of elements. This could also be interpreted as a consequence of some 
kind of focusing effect of the generated wave field. A small parametric study of the 
nominal angle (between 43 and 48 degree) actually resulted in a best correspondence when 
the angle was prescribed to be 47.5° in the model (see Table 4).  
 
ACKNOWLEDGEMENTS 
 
 The experimental data in this paper were conducted and generously provided by 
CEA in France, for this they are gratefully acknowledged. 
 The project is part of the TURBOKRAFT Research Programme, supported by the 
Swedish Energy Agency (STEM) and by Swedish industries such as Siemens Industrial 
Turbomachinery (SIT) and Volvo Aero Corporation (VAC). 
 
REFERENCES 
 
1. Wirdelius, H., SKI Report 00:29, Stockholm (2000). 
2. Boström, A. and Wirdelius, H., “Ultrasonic probe modeling and nondestructive crack 
detection”, J. Acoust. Soc. Am. 97, pp. 2836-2848 (1995). 
3. Boström, A., .SKI Report  95:53, Stockholm (1995). 
4. Boström, A. and Jansson, P.-Å., SKI Report 97:28, Stockholm (1997). 
5. Eriksson, A.S., Boström, A. and Wirdelius, H., SKI Report 97:1, Stockholm (1997). 
6. Bövik, P. and Boström, A., “A model of ultrasonic nondestructive testing for internal 
and subsurface cracks”, J. Acoust. Soc. Am. 102, pp. 2723-2733 (1997). 
2131
 
 
7. Rose, J. H., “Ultrasonic backscatter from microstructure”, Review of Progress in 
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Proc. World Congress on Ultrasonics WCU, 1, pp. 101-104 (2003). 
 
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