Strength Failure Conditions of the Various Structural Materials. Is there some Common Basis existing?

by Prof. Dr. Ralf Cuntze

Paper

The paper deals with the applicationof phenomenological, invariant-based strengthconditions (fracture failure) and their interrela-tionships. The conditions have been generatedand are just applied here for a variety of materials. These might possess a dense or a porousconsistency, and belong to brittle and ductile be-having isotropic materials, brittle unidirectional laminae and brittle woven fabrics. The derivation of the conditions was based on the author’s so-called Failure Mode Concept (FMC) which basically builds up on the hypotheses of Beltrami and Mohr-Coulomb. Essential topics of the paper are: ‘global fitting’versus ‘failure mode fitting’, a short derivation of the FMC, the presentation of the FMC-based strength failure conditions for the material families mentioned above, and the visualization of avariety of conditions. Various links or interrelationships between the materials are outlined. Conclusions which may be drawn from the laborious investigations:

1. The application of Beltrami’s assumption together with the consideration of material friction forms a common ba-sis in the determination of strength conditions.

2. The FMC is an efficient concept because itverystrictlyutilizes a ‘thinking in failure modes’as well as an application ofmaterial symmetry-related invariants.It has proven to be a help-ful tool in simply fitting the course of multi-axialstrength test data, and it finally can capture severalfailure modes in one equation avoiding the short-comings of the usual ‘global fitting’ strength con-ditions.

3. Different but similar behaving materi-als can be basically treated with the same strength condition.

Presentation

Seminarvortrag , Technische Universität Chemnitz
Strukturleichtbau und Kunststoffverarbeitung (SLK) 2. Juni 2009

Contents of Presentation

1  Introduction to Design Verification

2  Stress States & Invariants

3  Observed Strength Failure Modes and Strengths

4  Attempt for a Systematization

5  Short Derivation of the Failure Mode Concept (FMC)

6  Visualizations of some Derived Failure Conditions

   Conclusions