Clamping Geometry
Mechanical testing clamps secure rectangular polymer specimens at both ends while applying transverse bending displacement at the center span. A dual cantilever fixture constrains specimen end rotations to eliminate axial twisting during dynamic mechanical testing sequences. The arrangement imposes pure double bending deformation along the sample length, facilitating shear and flexural modulus extraction.
Applicability stops when sample thickness causes transverse shear deformation to dominate pure bending stress profiles. Testing soft elastomers requires alternative clamping arrangements to prevent sample tearing at fixed clamp edges.
Loading Mechanics
Rigid clamping blocks suppress specimen slippage during high force dynamic oscillations across wide temperature ranges. Thermal expansion differences between the metal fixture and polymer test sample generate clamping force changes during thermal scans. Torque wrench tightening standards maintain uniform clamping pressure across consecutive specimen mountings.
Indentation under clamps creates local stress concentrations that require geometrical correction factors during data analysis.
Calibration Protocol
System compliance calibration subtracts fixture frame deflection from total measured displacement values. Standard steel reference bars with known flexural stiffness establish drive motor calibration constants across operational frequencies. Mass compensation removes inertia forces generated by the moving center clamp structure at high frequencies.
Verification routines confirm baseline displacement accuracy before executing material characterization runs.
Measurement Boundary
Low stiffness samples flex excessively under self-weight, causing geometric non-linearity before mechanical testing begins. Extremely rigid samples exceed load frame displacement limits, producing signal noise in force transducers. Edge effects near clamping surfaces introduce multi-axial stress states that deviate from ideal beam theory assumptions.
Standard test methods specify specimen length to thickness ratios that ensure valid flexural modulus values.
