Abstract
The shadow optical method of caustics is a relatively new experimental technique in stress strain analysis. It was introduced by Manogg1,2 in 1964. The method is sensitive to stress gradients and therefore is an appropriate tool for quantifiying stress concentration problems. Manogg originally used the method for investigating crack tip stress intensifications. The technique was extended later by Theocaris3–5, Rosakis6,7, and the author and his colleagues8–11 to different conditions of loading, material behavior, in static as well as dynamic situations. Shadow optical images of test specimens under loading in general are characterized by very simple geometric patterns which can be easily evaluated. Because of the simplicity of shadow patterns, the method can also be successfully applied for investigating rather complex phenomena, for example transient problems. Despite the complexity which may be inherent in the problems to be investigated the clearness of the generated recordings allows the derivation of reliable informative data. The author and his colleagues have applied the caustic technique to investigate various problems of practical interest in the field of fracture dynamics, in particular to the behavior of propagating and subsequently arresting cracks and the behavior of cracks under different impact loading conditions.
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Abbreviations
- a:
-
Crack length
- a,b:
-
Elasto-optical constants
- A,B:
-
Material constants in Maxwell-Neumann’s law
- α:
-
Velocity dependent factor
- a2,3,4... :
-
Coeffients of higher order terms in crack tip stress distribution
- c:
-
Shadow optical constant
- co :
-
Sound wave speed
- c1 :
-
Longitudinal wave speed
- c2 :
-
Transverse wave speed
- C:
-
Compliance of specimen
- d:
-
1. Specimen thickness
2. Distance between two cracks in double crack configuration
- deff :
-
Effective thickness of the specimen
- D:
-
Characteristic length parameter for caustic evaluation
- Do,i :
-
Outer, inner characteristic length parameter
- Dmax,min :
-
Maximum, minimum length parameter of mixed mode caustics
- e:
-
Index characterizing elastic behavior
- E:
-
Young’s modulus
- ε:
-
Strain
- f:
-
Numerical factor for caustic evaluation
- fo,i :
-
Numerical factor for evaluating outer, inner caustic
- g:
-
Numerical factor for KI-determination from mixed mode caustics
- G:
-
1. Function
2. Lamé’s constant, G = E/2(1+ν)
- H:
-
Height of specimen
- In :
-
Numerical Factor in the HRR stress field equations
- J:
-
J-Integral
- K:
-
Stress intensity factor
- n:
-
1. Refractive index
2. Strain hardening coefficient
- ν:
-
Poisson’s ratio
- O:
-
Origin of coordinate system
- p:
-
Edge load, unit N/m
- P:
-
Index characterizing plastic behavior
- p,q:
-
Biaxial stresses in y,x-direction
- R:
-
Radius of circular hole
- r,φ:
-
Polar coordinate system in object plane (specimen)
- r′,φ′:
-
Polar coordinate system in image (reference) plane
- :
-
Polar coordinate system at the tip of a moving crack
- ro :
-
Radius of initial curve
- rpl :
-
Radius of plastically deformed region around the crack tip
- rps :
-
Smallest radius around the center of stress concentration outside which a state of plane stress exists
- ρ:
-
1. Density of the material
2. Notch tip radius
3. Wedge tip radius
- S:
-
Support span
- s:
-
Optical path length
- σ:
-
Normal stress
- σo :
-
Tensile yield stress
- t:
-
Time
- λ:
-
Coefficient of anisotropy
- τ:
-
1. Shear stress
2. Period of the oscillation of impacted specimen
- µ:
-
Ratio of the mode II to mode I stress intensity factor, KII/KI
- u,v,w:
-
Displacements in x,y,z-direction
- W:
-
Width of the specimen
- x,y:
-
Cartesian coordinates system in object plane (specimen)
- x′,y′:
-
Cartesian coordinates system in image (reference) plane
- :
-
Cartesian coordinates system at the tip of a moving crack
- z:
-
Direction of optical axis
- zo :
-
Distance between object plane (specimen) and image (reference) plane
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Kalthoff, J.F. (1987). The Shadow Optical Method of Caustics. In: Lagarde, A. (eds) Static and Dynamic Photoelasticity and Caustics. International Centre for Mechanical Sciences, vol 290. Springer, Vienna. https://doi.org/10.1007/978-3-7091-2630-1_4
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DOI: https://doi.org/10.1007/978-3-7091-2630-1_4
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