State Of The Art In Crack Propagation
C. Timbrell, R. Chandwani, G. Cook
Journée Scientifique 2004: Les méthodes de dimensionnement en fatigue, Centre de Compétences Matériaux & Conception (CCM&C), Fribourg, Switzerland, Oct 27 2004
Abstract:
This paper discusses the issues involved in numerical crack growth
prediction for general 3D cracks and describes the state of the art
methods that are available to practising engineers. This is a wide
ranging subject in which no single theoretical method is appropriate for
all cases. Different approaches are adopted, for example, for crack
propagation under static load, sustained load, fatigue load and impact
load. The historical pedigree of the various approaches dictates the
extent to which commercial software can provide practical solutions on a
day-to-day basis. A brief overview is given of the relevant fracture
mechanics parameters and their use in crack growth prediction under
various load conditions.
The difficulties imposed by real-life problems are further compounded by
the complex 3D geometries that are involved. These complexities may
arise from general component shape such as turbine disk-to-blade
connections or from individual geometric discontinuities such as
chamfers or stiffeners. Further complications may be introduced from a
variety of sources including residual stress effects, propagation along
dissimilar material interfaces and propagation in non-metallic materials
or metals which are non-homogenous, large grained or anisotropic.
A number of numerical approaches are discussed and the advantages and
disadvantages of each are noted. Difficulties associated with growth of a
general 3D crack front are considered in general and with respect to
each method.
Of the various load types that may cause crack propagation, fatigue is
the most advanced in terms of useable prediction capabilities. The
current state of the art for fatigue crack propagation allows for growth
of multiple non-planar defects through a 3D structure under general
mixed mode loading. Stress ratio and load interaction effects may be
included within the analysis. The most general integration schemes allow
for proprietary crack growth models, including stress ratio and
temperature dependency. In addition, the effect of a static load
component such as residual stress may be included within the analysis.
Sustained load damage (e.g. Creep) may be combined with instantaneous
damage due to rainflow counted fatigue cycles.