Method and device for sizing a crack in a workpiece using the ultrasonic pulse-echo technique

A method for determining the size of a crack in a workpiece, more specifically the depth of a crack in said workpiece, using the ultrasonic pulse-echo method, said method involving the following method steps:

• a workpiece is chosen having a front face and a back face, wherein the workpiece exhibits a crack starting at the back face,
• an angle beam probe is placed on the front face, the angle beam probe sends ultrasonic pulses at an angle alpha into the workpiece and receives echo signals of said pulses,
• the angle beam probe is moved at least once over the crack so that the radiation beam of the angle beam probe sweeps across the entire crack,
• the received echo signals are digitalized and stored in a memory as pairs of echo signal values over travel time, whereby the stored pairs of values form a multitude and an envelope curve is constructed of this multitude, wherein for the construction of the envelope curve the high values of the stored pairs are used,
• the size of the crack is calculated from the width of the envelope curve at a predetermined partial amplitude and from the maximum amplitude of the envelope curve.