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The Ultrasonic Impact Treatment (UIT) has been used in different materials to reduce residual welding tensile stresses and improve the fatigue life of welded joints, and also to increase the fatigue resistance at low temperatures. The main aim of this research was to explore the effects of UIT in the fatigue life of a 2024-T3 aluminium alloy. Load controlled fatigue tests were carried out at high and low cycle fatigue, and three UIT parameters at a carrier frequency of 36 kHz were evaluated. These parameters were feed rate, amplitude under load and impact frequency. The results revealed an increase in compressive residual stress and microhardness, as well as some evidence of porosity. However, the fatigue life was reduced drastically. The possible causes of this decrease are still under discussion.

Los aislantes anti vibratorios usados para reducir y controlar la respuesta de impacto suelen presentar propiedades no lineales a causa de los altos niveles de deformación, de su configuración geométrica y materiales. En particular, los aislantes basados en materiales visco elásticos y los resortes construidos usando cables de acero son notables por sus propiedades no lineales. Además, al ser sometidos a cargas cíclicas forman lazos de histéresis en su curva fuerza deformación. Sin embargo, el estudio de la respuesta de impacto se ha limitado a modelos que estudian las propiedades no lineales de forma independiente, o bien, que omiten el efecto del amortiguamiento. Por esta razón, este trabajo presenta un análisis de la respuesta de impacto considerando el modelo de Bouc-Wen para sistemas con histéresis. Este modelo es ampliamente usado para representar lazos de histéresis causados por efectos no lineales en amortiguamiento y rigidez. Se discuten los trabajos más relevantes y se presentan antecedentes breves sobre la respuesta al impacto y el modelo de Bouc-Wen. Posteriormente, se presentan resultados teóricos analizando y discutiendo la respuesta de impacto absoluta y relativa, para finalmente investigar el efecto del incremento de la amplitud de entrada en la respuesta del sistema. Se concluye que bajo ciertas circunstancias las propiedades no lineales pueden resultar benéficas para el diseño de aislantes de alto rendimiento para ambientes extremos. Descriptores: Impacto, aislantes de cable, amortiguamiento, fricción seca, rigidez no lineal.

Abstract. Two-degree of freedom system, or two-stage mount are used to improve the high frequency vibration isolation performance with the disadvantage of increasing the mass of the system and adding a second resonance. The vibration isolation property is a well-understood topic for harmonic vibration considering linear and nonlinear elements, but not its shock response. The absolute and relative response of a two-stage mount under shock excitation is investigated in this paper. Analysing the effect of the mass ratio between the two-stage, and its respective viscous damping. The potential advantages and issues behind this system are discussed and compared with the single mount. Experimental validation was performed using two commercial isolator and different masses. Findings suggested that a large secondary mass could reduce the shock response in terms of absolute motion. This effect is only significant for the case of short pulses and when the added mass is at least five times greater than the main mass. Being useful to have light damping only on the secondary stage.