Constitutive Modelling

Viscoelastic-Plastic-Fracture Modeling of Asphalt Mixtures

Viscoelastic-Plastic-Fracture Modeling of Asphalt Mixtures under Monotonic and Repeated Loads

A Journal paper published at Transportation Research Record (TRR) (Journal Link or Aston Research Explorer for full text)
VEPF Constitutive models
1. ViscoElasticity: Prony Series model
2. ViscoPlasticity: Generalized Drucker-Prager yield surface (for plastic initiation) + Perzyna's flow rule (for plastic flow)
3. ViscoFracture: Viscoelastic Griffith criterion (for cracking initiation) + Pseudo J-integral Paris's law (for cracking evolution)

von Mises stress in a cylinder asphalt sample modeled by ViscoElastoPlastic-Fracture (VEPF) constitutive models

Sample subjected to a monotonic load (constant-rate compressive strength test).
A very uniform distribution of the stress within the sample
We can see significant vertical compressive deformation during the loading

VPEF model predictions vs. Lab compressive strength test measurements

To remove the systematic errors (assumptions), we have to use a comprehensive constitutive model (e.g., VEPF model, rather than VE, VEP, etc.) to accurately predict the asphalt behaviors.
Plastic deformation becomes saturated at a later stage of loading, indicating a hardening effect
Cracking occurs after plastic deformation but before the peak stress.

Plastic Yield Surface Model for Asphalt

A generalized Drucker–Prager viscoplastic yield surface model for asphalt concrete

A Journal Paper at Materials and Structures (Journal Link or Aston Research Explorer for Full Text)
Extended Drucker Prager (EDP) Model vs. Generalized Drucker Prager (GDP) Model
- EDP yield surface becomes non-convex when friction angle > 22 degrees, conflict with Principle of Maximum Plastic Dissipation
- GDP yield surface remains always convex for all possible friction angles, can be used for various geo-materials

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