Method of and apparatus for detecting flaws inside articles, more particularly structural components, by means of acoustic holography

Claim 3

A method according to claim 1, characterised by superimposing two interferograms of different phases.

Claim 4

A method, according to claim 1, characterised by changing the carrier frequency between each two flaw pulses (I F ).

Claim 5

A method, according to claim 1, characterised by changing the distance (angle) of the testhead applying the ultrasonic pulses between each two flaw pulses.

Claim 6

Apparatus for detecting flaws inside articles, such as structural components, by acoustic holography, comprising a first unit (3) including an ultrasonic transmitter for generating triggering ultrasonic flaw pulses (I F ) and one of ultrasonic and electrical reference pulses (I R ), at least one test head (6, 6') connected to said first unit (3) for directing a flaw pulse (I F ) or a flaw pulse (I F ) and a reference pulse (I R ) into the flaw area of a test piece (1), a receiver (8) for the sound field of the flaw pulse (I F ) or the interference field of the flaw and reference pulise (I F +I R ) from the test piece (1), and a second unit (7) connected to said receiver (8) for producing holograms of the interference field, which in the case of a purely electrical reference pulse (I R ), comprises means for superimposing this electrical reference pulse (I R ) and the flaw pulse (I F ) after reaction of the latter with the flaw, characterized by a loading unit (2) arranged for applying a load to the test piece (1) the duration or period of which is long compared with the duration of the flaw pulse (I F ) and controls a control unit (11-15) connected to said first unit (3) for delivering the signal triggering said transmitter of said first unit (3) whenever the loading of the flaw reaches a predetermined extreme value (minimum and maximum in the case of cyclic loading, before the loading and at the maximum loading in the case of a single loading), said loading unit connected to said control unit, a third unit (4) connected to and controlled by the loading unit (2) for changing the relative phase between the flaw pulse (I F ) and the reference pulse (I R ) by a predetermined adjustable amount simultaneously with the sonic applications to the loaded flaw, and a fourth unit (9) connected to said second unit (7) for reconstructing and superimposing the holograms of the sonic applications to the flaw to form an interferogram, and an evaluator (10) connected to said fourth unit (9) for evaluating the interferogram.

Claim 7

Apparatus for detecting flaws inside articles, such as structural components, by acoustic holography, comprising a first unit (3) including an ultrasonic transmitter for generating triggering ultrasonic flaw pulses (I F ) and one of ultrasonic and electrical reference pulses (I R ), at least one test head (6, 6') connected to said first unit (3) for directing a flaw pulse (I F ) or a flaw pulse (I F ) and a reference pulse (I R ) into the flaw area of a test piece (1), a receiver (8) for the sound field of the flaw pulse (I F ) or the interference field of the flaw and reference pulise (I F +I R ) from the test piece (1), and a second unit (7) connected to said receiver (8) for producing holograms of the interference field, which in the case of a purely electrical reference pulse (I R ), comprises means for superimposing this electrical reference pulse (I R ) and the flaw pulse (I F ) after reaction of the latter with the flaw, characterized by a loading unit (2) arranged for applying a load to the test piece (1) the duration or period of which is long compared with the duration of the flaw pulse (I F ) and controls a control unit (11-15) connected to said first unit (3) for delivering the signal triggering said transmitter of said first unit (3) whenever the loading of the flaw reaches a predetermined extreme value (minimum and maximum in the case of cyclic loading, before the loading and at the maximum loading in the case of a single loading), said loading unit connected to said control unit, a third unit (4) connected to and controlled by the loading unit (2) for changing the relative phase between the flaw pulse (I F ) and the reference pulse (I R ) by a predetermined adjustable amount simultaneously with the sonic applications to the loaded flaw, and a fourth unit (9) connected to said second unit (7) for reconstructing and superimposing the holograms of the sonic applications to the flaw to form an interferogram, and an evaluator (10) connected to said fourth unit (9) for evaluating the interferogram.

Claim 8

Apparatus according to claim 5, wherein said control unit (11-15) includes a delay unit (11) by means of which the signal coming from the loading unit (2) for triggering the ultrasonic transmitter (3) is delayed by a preselectable amount Δ t 1 .

Claim 9

Apparatus according to claim 5, wherein said control unit (11-15) for triggering the ultrasonic transmitter (3) comprises an adjustment unit (12) for counting the extreme values or intermediate values of the loading, and a counter (13) which follows said adjustment unit (12), a comparator (15) having an input, an adjustment unit (14) arranged parallel to said counter (13) in said control unit (11-15) and connected to said comparator (15), said counter (13) is connected to the input of said comparator (15) for adjusting the interval of time between two ultrasonic applications, said comparator (15) delivers a pulse triggering the ultrasonic transmitter (3) when the values counted by the counter (13) give a time interval corresponding to the time between two ultrasonic applications.

Claim 10

Apparatus according to claim 5, including a selector means for the carrier frequency for the unltrasonic transmitter (3).

Claim 11

Apparatus according to claim 5, including a selector means for the distance (angle) of the ultrasonic test head (6, 6').