The stress meter detects the birefringence of transparent and weakly coloured materials and calculates the value of the birefringence with a precise optical range error of up to 10 nm by the Senarmont compensation method.
The distribution of the birefringence is also analysed by polarising the light.
The distribution and magnitude of the refractive index directly reflects the distribution and magnitude of the stress in the material.
When a material cannot be displaced by an external force, its geometry and dimensions will change and this deformation is called Strain.
When a material is deformed, a reaction force of equal magnitude but in the opposite direction is generated within the material to resist the external force, defining this reaction force per unit area as Stress.
Or when an object is deformed due to an external cause (force, change in humidity, etc.), an internal force is generated between the parts of the object that interact to resist this external cause and attempt to return the object from its deformed position to its pre-deformed position.
The internal force per unit area at a point in the section under investigation is called Stress.
According to the relationship between the direction of stress and strain, the stress can be divided into a positive stress σ and a tangential stress τ.
The direction of the positive stress is parallel to the direction of strain, while the direction of the tangential stress is perpendicular to the strain.
Stress can be divided into tensile and compressive stresses, bending stresses and torsional stresses according to the form of the load.
There is no deformation in the periphery of the inspected lens, that is, through the inspection of the stress meter, there is almost no strip or sheet-like smoke-like smoke-like pattern around the lens, which is the most ideal condition for fitting.
But this is difficult to do in the assembly, especially in the assembly of the full frame, because it is necessary to prevent the stress from being too weak and the lens cutting edge to be too small.
If the stress is too strong or the local is too strong, the shadows of the shape of dark clouds, smoke, etc. appear around the lens, which extend to the center of the lens in a radial shape with acute angles.
If the deformation is severe, the effective optical zone in the center of the lens will directly affect the wearer's corrected vision.
