• Combined dynamic-static loading and acidic corrosion cause significantly more severe mechanical degradation in shale than either single damage mode, with a 20% HCl treatment reducing peak strength to 158.97 MPa.
• The damage factor, characterized by longitudinal wave velocity, increases with acid concentration, indicating a direct correlation between acid exposure and shale structural damage.
• Energy analysis reveals that combined damage reduces total and elastic strain energy while increasing dissipated energy, leading to more developed fractures and severe failure.
• Microstructural analyses (XRD and SEM) show that acid erosion reduces carbonate content and, when combined with mechanical pre-damage, accelerates acid-rock reactions, increasing micro-interfacial pores and degrading structural integrity.