Isotropic Material Testing for Ultra High Strength Steel Enclosures
Verify multi-axial yield limits and planar plastic strain ratios across three sheet axes to prevent catastrophic battery enclosure tearing under crash loads.
Hydraulic Bulge Testing
Meaning
Experimental methodology for material testing evaluates the mechanical properties of sheet metals under tension conditions. The process of hydraulic bulge testing uses high-pressure fluid to deform a circular or elliptical specimen clamped over a die, creating a dome-shaped bulge. Unlike conventional uniaxial tension tests, this method avoids frictional effects and allows the material to reach much higher strain levels before failure occurs.
Sourcing departments use the resulting stress-strain curve to design metal forming processes with high accuracy.
Biaxial Deformation
Equibiaxial stress states are generated at the apex of the dome during the bulge expansion. This loading state is representative of the actual conditions that sheet metals experience during deep drawing or stamping. It enables the measurement of material behavior up to the point of plastic instability.
Experimental Configuration
Clamping dies and a hydraulic pump are the fundamental components of the test equipment. An optical measurement system tracks the height of the dome and the strain distribution at the apex in real-time. The pressure of the fluid is synchronized with these deformation measurements to calculate the flow stress.
Analytical Modelling
True stress is calculated using the pressure of the fluid and the curvature radius of the deformed dome. This stress value is plotted against the true strain to construct the biaxial hardening curve of the sheet. This curve is then used to calibrate plastic yield criteria for simulation software.