Relationship resilience - tenacity. The contributions of numerical modeling

The Charpy test, proposed more than a century ago, is the subject of renewed interest due to experimental developments and considerable progress in numerical modeling of material behavior, damage and fracture.

Numerical modeling currently enables us to adequately describe the elasto-viscoplastic behavior of materials, ductile tearing and brittle fracture within the framework of the local fracture approach.

On the occasion of the centenary of the Charpy test, a conference reviewed developments in its experimental aspects and the modeling used to determine the ductile-fragile transition of various materials. In general, the aim is to derive characteristics that can be used in structural design, in particular resistance to crack propagation and fracture toughness.

This dossier presents some aspects of numerical modeling of the Charpy test and its use to predict "toughness" as part of the local approach to fracture.

To model the Charpy test, we need to study the influence of the following conditions:

• characterization of mechanical fields and development of plasticity ;

• inertia effects ;

• stiffness of test machine ;

• contact conditions ;

• temperature rise due to plastic deformation and rapid loading ;

• two- or three-dimensional simulation ;

• effect of ductile tearing.

The application of the local fracture approach to predict toughness in the ductile-fragile transition is then presented. The focus is on materials exhibiting brittle and ductile fracture, as well as a transition within a defined temperature range.

The applications deal with the case of metals, but the approach is general. First, it is necessary to determine precisely the mechanical variables used in the brittle fracture prediction model. Thus, we first present the modeling of the toughness test and the Charpy test at the bottom of the ductile-brittle transition. We then examine the influence of ductile tearing on cleavage initiation in the transition region.