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The purpose of this study is to model and understand the role of an applied mechanical stress in piezoelectric materials as far as electroacoustic parameters are concerned. In the field of thick or thin film technology, understanding and predicting the behavior of integrated structures when submitted to external or internal mechanical stress is of primary importance. Thus, we propose a modified KLM electroacoustic model of transducer that enables to take into account the effect of a mechanical pre-stress. Then, a numerical study of the electroacoustic parameters for lithium niobate piezoelectric material (coupling coefficient, velocities, associated polarizations, and electrical input impedance) is conducted with regard to the azimuthal and elevation angles, as well as initial pre-stress values. Finally, we study the pulse-echo response of a complete piezoelectric transducer consisting of a piezoelectric film laid down upon a backing material and matching layers, with and without an initial stress, to highlight some benefits of a prestress load.