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Notes: The performance of an ultrasonic cutting device critically relies on the interaction of thecutting tool and the material to be cut. A finite element (FE) model of ultrasonic cutting isdeveloped to enable the design of the cutting blade to be influenced by the requirements of the toolmaterialinteraction and to allow cutting parameters to be estimated as an integral part of designingthe cutting blade. In this paper, an application in food processing is considered and FE models ofcutting are demonstrated for toffee; a food product which is typically sticky, highly temperaturedependent, and difficult to cut.Two different 2D coupled thermal stress FE models are considered, to simulate ultrasoniccutting. The first model utilises the debond option in ABAQUS standard and the second uses theelement erosion model in ABAQUS explicit. Both models represent a single blade ultrasoniccutting device tuned to a longitudinal mode of vibration cutting a specimen of toffee. The modelallows blade tip geometry, ultrasonic amplitude, cutting speed, frequency and cutting force to beadjusted, in particular to assess the effects of different cutting blade profiles.The validity of the model is highly dependent on the accuracy of the material data input and onthe accuracy of the friction and temperature boundary condition at the blade-material interface.Uniaxial tensile tests are conducted on specimens of toffee for a range of temperatures. Thisprovides temperature dependent stress-strain data, which characterises the material behaviour, to beincluded in the FE models. Due to the difficulty in gripping the tensile specimens in the testmachine, special grips were manufactured to allow the material to be pulled without initiatingcracks or causing the specimen to break at the grips. A Coulomb friction condition at the bladematerialinterface is estimated from experiments, which study the change in the friction coefficientdue to ultrasonic excitation of a surface, made from the same material as the blade, in contact with aspecimen of toffee. A model of heat generation at the blade-toffee interface is also included tocharacterise contact during ultrasonic cutting. The failure criterion for the debond model assumescrack propagation will occur when the stress normal to the crack surface reaches the tensile failurestress of toffee and the element erosion model uses a shear failure criterion to initiate elementremoval. The validity of the models is discussed, providing some insights into the estimation ofcontact conditions and it is shown how these models can improve design of ultrasonic cuttingdevices