Ultrasonic flaw detector and ultrasonic flaw detecting method for composite material

An ultrasonic flaw detector for a composite material, the composite material including a first material made of CFRP, a second material made of GFRP, and an interface disposed between the first material and the second material, each of the first material, the second material, and the interface having different physical properties from one another, the composite material formed by laminating the first material and the second material, the ultrasonic flaw detector comprising:

• a section specifier configured to specify first and second sections of an RF signal of a reflected wave of an ultrasonic wave with which the composite material is irradiated, a material reflected wave being generated in the first section, an interface reflected wave being generated in the second section, the interface reflected wave having a positive peak and a negative peak when an interface flaw exists at the interface;
• a material flaw determiner being configured to determine whether or not a material flaw exists by determining whether or not a value of the RF signal exceeds a positive first threshold in the first section;
• and
• an interface flaw determiner being configured to determine whether or not the interface flaw exists only by determining whether or not the value of the RF signal falls below a negative second threshold in the second section, the negative second threshold being a negative value less than 0, wherein
• the ultrasonic flaw detector is configured to cause an ultrasonic transmitter to irradiate the composite material from a first material side of the composite material so that the positive peak and the negative peak of the interface reflected wave are generated when the interface flaw exists at the interface.