Fracture toughness of frozen meat

The fracture toughness and dynamic mechanical moduli of frozen beef M. semitendinosus were investigated at various sub-zero temperatures using several different test geometries. Traditional fracture mechanics methods were considered inapplicable to frozen meat, since considerable plastic flow occurs in addition to elastic deformation and fracture. Graphical work area methods still apply, based on calculating areas under load-deflection diagrams to measure the energy used up to fracture. Total work to fracture was found to vary both with temperature and geometry, with a peak occurring between -10°C and -15°C. It was shown that it is possible to separate out the components of fracture and flow using two methods: microtome cutting and compact tension. In microtome cutting, the cutting energy was found to depend on the thickness of cut, increasing linearly from 50 μm to 500 μm. This variation is attributed to a dependence of the volume of the plastic zone size at the cutting tip on the thickness. By extrapolation to zero thickness, an essential value of fracture energy of approximately 100J/m(2) was determined, assuming the absence of large-scale plastic yielding. It was also possible to determine a value for the essential work of fracture using graphical work area methods in compact tension, obtaining values between 100 and 200 J/m(2). Dynamic mechanical testing showed loss peaks in mechanical damping occurring between -5°C and -10°C, with both temperature and magnitude of these peaks varying with frequency. Cryo-scanning electronic microscopy showed evidence of the nature of the fracture transition within frozen meat, indicating ductile deformation at higher temperatures (above -15°C), and brittle fracture at lower temperatures (below -15°C).