Material Data

Key requirement for calculation of distortions and stresses is a proper material definition. Simufact Welding offers a comprehensive material database Simufact Material, allowing management of material data sets and providing a number of different material data sets to start with. In a standard configuration Simufact Welding takes complex non-linear material behavior into account, like work hardening and temperature dependent material properties.

Additional module Advanced material models extends these capabilities by taking metallurgical phase transformations in steels into account, especially calculating the phase proportions and resulting effects on stresses, distortions material properties.

 

Simufact Material Database

Simufact Material: More than just material data

Simufact Material is a powerful tool with wide abilities of material data management and editing.

Simufact Material comes with a variety material definition usable in a welding simulation. Those materials include austenitic, low-alloyed, tool and casehardening steels, most common aluminum alloys as well as examples of titanium, nickel-based, copper-based and cobalt-based alloys.

Simufact Material GUI with applied filter for welding application
Simufact Material GUI with applied filter for welding application

Material data is usually extended and improved with every release. A dataset for material definition includes density, Young’s modulus, Poisson’s ratio, thermal expansion coefficient, solidus and liquidus temperatures as well as melting enthalpy, thermal conductivity, thermal capacity as well as stress-strain-relations. For resistance spot welding simulation electrical properties are also included. Furthermore, for steels undergoing metallurgical phase transition, the transformation data is also included.

All data sets are, as far as it makes sense for welding simulation, defined with respect to temperature as tables defined between room temperature (usually at 20°C) and melting temperature of the materials. Tables can be exported in CSV format or be edited directly in the Simufact Material GUI. Additionally, it is possible to apply mathematical functions on tables, changing all values at once according to some known formula.

Stress-strain-curves can be defined with respect to temperature, strain rate and peak temperature. The peak temperature dependency can be used to model the behavior of aluminum alloys in the heat affected zone, changing yield stress due to precipitation hardening under influence of temperature. Additionally, it is possible to scale a given stress-strain dataset with respect to measured Rp0.2 and Rm stress values directly in the GUI.

Example of stress-strain curves defined with respect to peak temperature
Example of stress-strain curves defined with respect to peak temperature

Phase transformation data includes t85-dependencies for tensile and proof stress as well as expected hardness and transformation strains. All other material properties are calculated during the simulation by applied mixing rules.

 

Import of external material data

Simufact Material supports data import from JMatPro®, Matilda and MSC Mentat.

Material data can be calculated with JMatPro® from our partner Sente Software. This calculation is based on the individual chemical composition of the alloy and the thermal history of the material:

  • From room temperature up to 1400°C
  • Up to the material’s melting point
  • For true strains up to 4

For general steels, in addition to material data needed for forming simulation (like thermophysical, mechanical, and plastic properties), phase transformation diagrams are provided for welding simulation.

For stainless steels, general steels, aluminum and titanium, it is possible to calculate all properties needed for forming simulation.

Material data can be purchased for a single alloy, in packages of five or ten alloys, and subsequently be imported into the Simufact Material database.

Material models in welding simulation

Influencing physics for material models

Simufact Welding calculates welding distortions and residual stresses based on temperature-dependent elastic-plastic material model with hardening. The influence of material properties at temperatures above the melting point is usually neglected. The thermal expansion of the liquid phase is prevented by a proper definition of the coefficient of thermal expansion, while effective plastic strains that define the evolution of hardening are set to zero until the temperature falls below the solidification temperature of the material. For a large number of metallic materials, this approach is sufficient for the calculation of welding distortions. However, residual stresses and tensile strength are usually influenced by more complex material laws.

Possible mechanisms that influence material behavior are: work hardening, softening due to grain coarsening inside the melt pool, phase transformations (including hardening due to the creation of bainite and martensite, as well as transformation strains and transformation induced plasticity), dilution, and precipitation processes. The following materials are particularly affected by those phenomena:

  • High and low alloyed steels (notably phase transformations)
  • Aluminum alloys (4xxx, 6xxx, 7xxx, notably dilution and precipitation processes)
  • Titanium alloys
  • Nickel based alloys

 

Models and Approaches for Critical Mechanism

Work hardening, softening by grain coarsening in the melt pool

Work hardening, which is set to zero during welding inside the melt pool, can be implemented using pre-state functionality if it results from a process chain before welding (for instance, due to a forming process). Alternatively, it is possible to define global hardening using the GUI.

Residual stresses during welding of a metal sheet without (left) and with pre-hardening.
Residual stresses during welding of a metal sheet without (left) and with pre-hardening.

Dilution and Precipitation Processes

Micro-tensile tests of an aluminum welded sample
Micro-tensile tests of an aluminum welded sample (Source: Stiftung Institut für Werkstofftechnik, Bremen)

A detailed implementation of dilution and precipitation processes is usually economically impossible. Micro-tensile tests in different regions of the sample can provide the necessary data.

Temperature- and peak temperature dependent stress-strain-curve in Simufact Material GUI
Temperature- and peak temperature dependent stress-strain-curve in Simufact Material GUI

A detailed implementation of dilution and precipitation processes is usually economically impossible. Micro-tensile tests in different regions of the sample can provide the necessary data.