Meaning
Calculation of the ratio between transverse stress and the resulting shape change defines the rigidity of a solid under sliding forces. Shear modulus is a fundamental parameter in the structural modeling of battery packs, especially for the adhesives and potting compounds used to secure cells. It marks the boundary where a material shifts from resisting shape change to yielding under sliding stress.
Material Relationship
Values for this constant correlate with the Young modulus and the Poisson ratio of the substance. For isotropic materials, the shear modulus is approximately one third to one half of the tensile modulus. This relationship allows engineers to predict how a component will behave under complex twisting loads.
Damping Characteristic
Soft polymers with a low value for this property effectively absorb mechanical vibrations. Choosing a thermal interface material with the correct shear modulus prevents the transmission of road noise through the battery frame. The material must remain flexible enough to accommodate the different thermal expansion rates of the joined parts.
Measurement Technique
Torsional vibration tests or direct shear loading in a rheometer provide the necessary data points. By applying a known force and measuring the angular displacement, the shear modulus can be calculated with high precision. Changes in the result over a temperature range reveal the glass transition point of the polymer.
Because the properties of thermosetting resins change significantly as they age, periodic testing of cured samples is necessary to ensure the structural integrity of the battery assembly over its design life. This long-term stability is a primary factor in selecting the chemical base for the potting compound.
