Abstract
It is known that a peculiar sound is produced when metallic or plastic material is cracked. This sound, caused by elastic waves generated by the release of strain energy stored in a solid during its plastic deformation, is called acoustic emission. Since acoustic emission is composed of elastic waves, an initial fracture point can be determined by measurement of the lag in elastic wave arrival time. Also the amount of energy released at the time of cracking of a solid object can be calculated by application of the destruction theory of Griffith which specifies the amount of energy released as the function of cracking area.Thus precise quantitative analysis of the cracking phenomenon of solid material is possible by means of acoustic emission measurement. However, acoustic emission in biological materials has so far been little studied. Perceiving the usefulness of acoustic emission in biological materials, the author attempted to examine the mechanism of bone fracture by detecting the initial point of fracture and calculating the amount of energy released. The experimental material consisted of a humerus, radius, femur, and tibia from a 3-year-old mongrel dog weighting 16 kg, and theedentulous mandible from an Indo-European male of estimated 60 years age. The materials were subjected to a three-point bending test. The acoustic emission in this test was picked up by acoustic emission sensors (s 9220, Physical Acoustic Co.), its amplitude magnified with a preamplifier (122 A, Physical Acoustic Co.), and the data analyzed with an acoustic emission analyzer (LOCAN Jr, Physical Acoustic Co.).The initial fracture site was ascertained from the lag in acoustic emission arrival time, frequency of acoustic emission, maximum amplitude of acoustic emission, and distribution of maximum amplitude. The amount and ratio of energy release were also calculated.The following conclusions were drawn from this study:1. It is possible to determine the initial fracture point and to follow the exact phases of the fracture process.2. Prediction of the fracture time based on increased frequency of acoustic emission seemed difficult because the total frequency of acoustic emission varied structurally with a load-strain increase.3. By calculating the ratio of energy release it seemed possible to predict the extent of bone fracture under d given load.
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