Evaluation method

An evaluation method, comprising

• evaluating a percentage of voids in a rubber material with a strain applied thereto based on a φvoid calculated from the following Equation (1) using a transmittance and thickness of the rubber material with no strain applied thereto and a transmittance and thickness of the rubber material with the strain applied thereto,
• ∅
• void
• =
• 1
• -
• p
• s
• /
• p
• 0
• =
• 1
• -
• l
• ⁢
• n
• ⁢
• (
• I
• s
• I
• 0
• )
• /
• l
• ⁢
• n
• ⁢
• (
• I
• I
• 0
• )
• ×
• (
• t
• 0
• /
• t
• s
• )
• (
• 1
• )
• wherein
• ρ0:
• a density of the rubber material with no strain applied thereto,
• ρs:
• a density of the rubber material with the strain applied thereto,
• I/I0:
• the transmittance of the rubber material with no strain applied thereto,
• Is/I0:
• the transmittance of the rubber material with the strain applied thereto,
• I0:
• an intensity of a beam incident on the rubber material,
• I:
• an intensity of the beam transmitted through the rubber material with no strain applied thereto,
• Is:
• an intensity of the beam transmitted through the rubber material with the strain applied thereto,
• t0:
• the thickness of the rubber material with no strain applied thereto, and
• ts:
• the thickness of the rubber material with the strain applied thereto.