Measurement of coefficient of thermal expansion of films using digital image correlation method

High-temperature deformation field measurement by combining transient aerodynamic heating simulation system and reliability-guided digital image correlation

Laser speckle based digital optical methods in structural mechanics: A review

In this paper, a digital speckle correlation method for coefficient of thermal expansion (CTE) measurement of film is developed, in which CTE is the intrinsic parameter and direct variable. Deformation pattern governed by the CTE and temperature is used to affine transform the image captured after the film is heated. If the values of CTE are properly chosen, the image after affine transformation will have a highest similarity to the original image. This turns CTE measurement into a purely numerical search of an optimal trial CTE. Results of CTEs from this method and conventional DIC methods are compared with the actual CTE, showing an improved accuracy.

Deformation-pattern-based digital speckle correlation for coefficient of thermal expansion evaluation of film

A mesoscale study of thermal expansion behaviors of epoxy resin and carbon fiber/epoxy unidirectional composites based on periodic temperature and displacement boundary conditions

Carbon fibre composites find wide applications in aerospace, sporting goods industry and biomedicine. Mechanical and thermal properties of such materials are highly anisotropic; therefore, adequate experimental measuring methods are requested to determine them. This paper describes the application of electronic speckle pattern interferometry to full-field, real-time char- acterisation of the coefficient of thermal expansion (CTE) of anisotropic materials. The topics such as correlation fringes tilt and influence of small rigid body rotation were theoretically described and experimentally verified. A series of measurements was carried out to determine the CTE tensor for unidirectional and bi-directional carbon fibre laminates and to prove the feasibility of the method. The measuring set-up developed includes a temperature control unit for cooling and heating and a one-dimensional in-plane speckle interferometer.

Characterisation of Thermal Expansion Coefficient of Anisotropic Materials by Electronic Speckle Pattern Interferometry

The springback of the sheet metals after large deformations during deep drawing is not a strongly linear process with a constant Young’s modulus, but the stress–strain behaviour during the unloading phases shows considerably non-linear and inelastic effects. Unloading of two types of steel sheets for cold forming, a cold-rolled high-strength microalloyed steel and a low-carbon steel sheet, has been analysed using the method of electronic speckle pattern interferometry (ESPI). The specimens were investigated by uniaxial tension tests, and the influences of different testing parameters upon springback were analysed. The experimental measurements showed that the stress–strain curve during unloading is non-linear, the influence of the prestrain path upon unloading is minor, and the secant moduli of unloading curves decrease with increasing prestrain. When the prestrain value becomes high enough, a saturated value for the secant modulus is approached. An empirical relation was found to describe the changes in the unloading modulus in accordance with the prestrain value.

M. Stockmann

Papers

Characterisation of Thermal Expansion Coefficient of Anisotropic Materials by Electronic Speckle Pattern Interferometry

Investigation of Non‐Linear Springback for High Strength Steel Sheets by ESPI