Marine NDE (Spain) used the technical advantages of our Shearography-System for non-destructive examination (NDE) of large areas. The Combination of the SE sensor with the Piezoshaker system for dynamic loading helped the crew to inspect the large yacht hull (see image below). The hull with a lenghts of 30,5m was a advanced-composite and part of high performance sailing yacht in build. Because of the full-field method (100% of the inspected area is examined) testing the entire hull required only 240 shots, in three workdays.
The yacht hull consists of a sandwich construction, where are in particular used honeycomb cores.
On the left – A shearogram of a detected bonding defect (in red oval). The yellow X marks the location of the core sample shown at the right. The destructive test confirms the shearogram’s indication that there is a significant never-bond between the honeycomb core material and the film adhesive in this area.
The test panel was an original section of a wind turbine blade with a defect (a foam block with bridges). Previously the defect was located by infiltration of color through small drilled holes. The sample is examined non-destructively by the SE-Sensor.
right: Time average result at frequency of 2569Hz showing the debonding area.
left: Live view of surface including shearing.
right: Time average measurement from the marked area in the live image.
De-bonding of resin bridges
A GFRP sandwich with foam blocks and resin bridges should be examined. The detection of the defect type und structure is very quick and reliable in this case, because the defects are visible, not only at their local natural frequencies, but also due to their forced deflection shapes over a wide frequency bandwidth.
The excitation frequencies of the selected measurements are 1398 Hz (1), 3133 Hz (2), 2442 Hz (3) and 4906 Hz (4) – numbering in following images:
Air inclusion or air pockets in modern Li-battery packs is a serious and dangerous problem. The isi-sys SE2 sensor is able to detect tiny and large defects such as air bubbles, air pockets, cracks and other within a second. The defects can be far below or near to the surface. An example of a battery pack (test sample from University of Munich, IWB) and the measurement result is shown below.
The test has been done by SE2 sensor in combination with a glass vacuum chamber for a simple manual test. This is an economic solution for spot NDT by manual service. For automated series test in production different setups are required.
The battery packs are tested by small pressure differences of some mbar, which can be applied in seconds or below in small chambers. The sensor is monitoring the surface of the battery pack while the pressure is changed, measuring the differential deformation of the surface. Due to the expansion of the air bubbles and air pockets, the air inclusions can be located such as shown in the following images.
The first image shows the live view of the battery pack from the sensor. The second shows the recontructed phase, which is corresponding to the local deformation gradient.
Generally the required pressure difference depends on the defect depth, defect size an the mechanical stiffness of the tested structure, but in general the load is small due to the high sensitivity of the sensor detecting differential deformations of the surface.
This example combines the Vibrografie System with a Piezoshaker Modul for a non-destructive inspection. The heat shield with C-Si-C (carbon fiber-silicium composite) of the prospective recovery vehicle/ spacecraft x38 was reviewed by Shearography.
For an easier handling the Piezoshaker module is compressed on the surface of the object via suction base .
(a) Piezoshaker module, (b) the heat shield of the spacecraft X38 (c) Flight of the spacecraft X38.
The picture shows the determination of times of the heat shield with the natural frequency (1400 Hz).
Local vibration forms of defects at 10kHz and 18 kHz of the nose hood in the marked area of the image. During the inspections two defects have been detected at the upper area of the dog.
First test NDT Measurement by shearography on a wind turbine blade in 1996 by P. Mäckel, L. Yang, G. Kupfer and A. Tiemich at Kassel University. The object is a special wind rotor blade of a single wing wind turbine energy plant.
Applied loading method: Loading by internal pressure (the blade has been sealed). A manual pump has been used to increase a pressure difference against the surrounding. The fringe images show areas at different locations. The fringes are proportional to the out of plane deformation gradients of the surface, which allows to identify inhomogeneous stiffness of the structure: left – Delamination; right – Axial crack; center -Structural change over (different number of glasfiber layers).
The example shows an application of NDT on a 30m CFK yacht mast (lower left). The time average result of the SE1 measurement and dynamic loading by our piezo-shaker (lower right) is indicating a larger delimitation below the surface starting from a small visible crack. Usually small cracks are often seen on the surface, but not all are related to delamination, which needs any repair.
Setup for measurement on a rudder by dynamic loading.
The direct rigid mounting of the sensor on the rudder by the suction cups allows outdoor measurement even at strong winds with high flexibility. The high quality interference filters of the sensor permits measurement under day light conditions.
A: 9,3 kHz B: 7,5 kHz C: 5,5 kHz
Measurement results (time average) showing local vibration modes of defects due to reduced or inhomogeneous stiffness of the material. Even if a big field of view is selected, it is possible to detect small defects. Defect size and type as well as the depth of the defect (delamination) determine the normal modes (resonance frequency) of the local defect area.