Experimental study on the instability at a V-shaped interface accelerated by a strong shock wave with a Mach number exceeding 3.0 is performed in a shock-tube facility. To highlight the effect of initial amplitude on flow evolution, five V-shaped interfaces with various initial amplitudes are considered. Several interface evolution features differing significantly from those under weak shock conditions are observed, such as the secondary vortices on the spike stem and reverse jets at the spike root. For the linear evolution period, existing models exhibit limited predictive capability because they cannot effectively describe the strong flow compressibility and the intricate coupling between interface-geometry, shock-proximity, and secondary-compression effects. To overcome this limitation, we propose a modified model that combines a compressible linear theory to cover strong compressibility and a reduction factor to describe the coupling of the three effects. This model is applicable under both weak and strong shock conditions. In the nonlinear period, the amplitude evolution law is positively correlated with the initial amplitude due to the enhanced Mach-reflection effect under higher initial-amplitude conditions. None of the nonlinear models is effective under all initial-amplitude conditions, as they fail to account for the coupling influences of the Mach-reflection effect, geometric effect, shock-proximity effect, secondary-compression effect, and Kelvin-Helmholtz instability on nonlinear evolution. To bridge this gap, we propose parametrizing the composite mechanism through correction factors explicitly expressed as functions of initial amplitude and Mach number and develop an empirical nonlinear model that achieves favorable predictive performance across a broad range of initial-amplitude conditions.

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• Richtmyer-Meshkov instability
• Shock waves