Spectral-Response Overestimation in Student-Built Engineering Education Vibration-Absorber Test Rigs: A Shaker-Table Transmissibility Evaluation Linking Accelerometer Crosstalk to Mount-Fatigue Life Prediction

Student-built vibration-absorber test rigs are widely used in engineering education to demonstrate transmissibility and to estimate mount-fatigue life, yet the accelerometers mounted on these rigs are rarely characterised for cross-axis sensitivity. The model treats the measured transmissibility as a perturbation of the true transmissibility by a crosstalk term whose magnitude depends on the ratio of cross-axis to on-axis sensitivity and on the phase relation between the two orthogonal response components. A first-order sensitivity analysis yields a closed-form bound on the relative transmissibility bias, and a Basquin-type fatigue inversion translates that bias into a multiplicative life-prediction error. The analysis is a methodological and theoretical contribution: no experimental data are reported, and the model is intended to specify the calibration and reporting practices that student rigs require. The principal result is that crosstalk of the order commonly encountered in low-cost piezoelectric accelerometers can produce transmissibility bias sufficient to inflate predicted fatigue life by a factor that depends on the S-N slope, and that the bias is not eliminated by averaging over repeated runs. The paper concludes that transmissibility-based fatigue estimates from student rigs should be reported with an explicit crosstalk-uncertainty interval rather than as point predictions.