Determination of Young's Modulii and damping ratios of flexible hoses from experimental modal analysis

Hose pipes have numerous applications, a common one being in an engine, where they are used to transfer fuel, oil and water from one location to another. One of the most common causes of failure of these hoses is vibration, which may even lead to damage of the engine. Many of these hoses are of rubber with metallic braiding and Young's modulus of the combination of materials is generally unknown. In the present work, experimental modal analysis is used to calculate the Young's modulii of four different composite flexible hose pipes. These hoses were clamped at both ends and Frequency Response Functions (FRFs) were obtained. Since roving impact excitation did not yield good FRFs due to the high flexibility and damping of the hoses, an electrodynamic shaker was used to excite them and the force was measured using a piezoelectric transducer. A non-intrusive laser vibration transducer was roved along the hose to obtain FRFs. The first few natural frequencies, up to the third (it was difficult to capture modes higher than the second in some cases because of the high flexibility) were extracted from the FRFs by peak pick method. The hoses were idealized as Euler-Bernoulli beams and knowing their densities (which were measured in the laboratory) and geometries, the Young's modulii were determined from the analytical expression for the natural frequency of a beam. Average Young's modulii were calculated using up to three modes of vibration. Later on for validation purpose, the same Young's modulii were used in finite element analysis, along with experimentally measured damping ratios and FRFs were computed. In order to ensure that the same modes were being used for comparison in experiment and analysis, the mode shapes were compared using Modal Assurance Criteria (MAC). Comparison of experimental and analytical natural frequencies shows very good correlation.