Parametric visco-hyperelastic constitutive modeling of functionally graded 3D printed polymers

Grayscale masked vat photopolymerization (MSLA) 3D printing enables the fabrication of graded structures from a single material, overcoming a major limitation of vat photopolymerization methods. Two main parameters affecting the curing of the resin in vat photopolymerization , and thus the resulting material properties, are the exposure time per layer and the intensity of the ultraviolet light, which can be regulated in terms of the grayscale value of the mask.

In this work by Mr. Valizadeh and Prof. Weeger from the Cyber-Physical Simulation Group at TU Darmstadt, the concept of grayscale MSLA is extended by combining these two easily adjustable parameters into a single parameter, which is called the grayscale exposure. Then, a parametric visco-hyperelastic constitutive model is formulated for the strain rate-dependent behavior of the resulting material in finite deformations, which depends on the grayscale exposure. Hyperbolic tangent functions are utilized to express the dependency of the material coefficients in terms of grayscale exposure.

The advantage of expressing the material model in terms of grayscale exposure is not only the reduction of design parameters from two to one, but also the fact that the printing time can be reduced through the correlation of exposure time and grayscale. Furthermore, the grayscale exposure values are verified through a comparison of different couples of grayscale and exposure time. Finally, the constitutive model is validated against further experimental results, showing a good agreement.

In summary, the main contributions of this manuscript are the systematic investigation of the correlation of process parameters with rate-dependent mechanical properties, the unification of light intensity and layer printing time into the grayscale exposure as a single adjustable design parameter, as well as the development of a parametric visco-hyperelastic constitutive model and its experimental identification and verification.

Further information on this work can be found in the recently published article in the International Journal of Mechanical Sciences:

Valizadeh, O. Weeger: “Parametric visco-hyperelastic constitutive modeling of functionally graded 3D printed polymers”, International Journal of Mechanical Sciences 226:107335 (2022)

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