4RD SEMESTER, MECHANICAL
PRESENTATION:
PHOTOELASTICITY. GROUP MEMBERS: 1. SYED
ANIS BADSHAH
ME-001
2.
HAFIZ ABULRAFAY
ME-011
3.
MUHAMMAD ASHIQ
ME-037
4.
HAMMAD HABIB
ME-043
5.
MUHAMMAD HASHIM
ME-046
SUBMITTED TO:
ENGR; MUAZAMA ARSHAD
DEPARTMENT; MECHANICAL ENGG;
4RD SEMESTER, MECHANICAL
OUTLINE:
Definition and methodology of photoelasticity? Theory of Photoelasticity Photoelasticity
The application application of photoelasticity photoelasticity
Photoelastic Photoelastic materials
Products
GFP2000 for real-time photoelasticity photoelasticity PhotoStress Measurement
Limitations
Conclusions
PHOTOELASTICITY: —
”It is an indirect method of stress analysis, in that a study is made of the stress conditions in a scale model made from a transparent plastic material, and from this the stresses in a metal component can be deduced, both quantitatively and qualitative results being obtain.."
Polarized light is passed through the model in stress condition and changes the passage of light are thus effected , which are observed on the image of the model at the end of the optical system. The appearance appearance of an optical stress pattern pattern is illustrated illustrated in figure (A) (A) for a pair of mating gear teeth. These optical optical results are related to; 1. Stress distribution 2. Magnitude and 3. Direction in the model This provides provides stresses in the Actual metal component. component. Model is made of plastic And component of metal is Of no significance in Determination of stress in the elastic range
DEPARTMENT; MECHANICAL ENGG;
4RD SEMESTER, MECHANICAL
Because widely different elastic constants would only affect the determination of deformations and not stresses.
THEORY OF PHOTOELASTICITY: Photoelasticity is the application of given stress to the model which is made of
plastic or any other transparent material. After this we pass polarized light through the model which is composed of a transparent material and we utilize an induce birefringence (double refraction) , through this we examine the actual distribution of stresses of the material.
DEPARTMENT; MECHANICAL ENGG;
4RD SEMESTER, MECHANICAL
Birefringence(Double Refraction) A transparent material like mica, calcite etc is birefringent if a ray of light passing through it experiences two refractive refract ive indices, usually two rays are “ordinary and extra ordinary rays” . The effect of this is to change the polarization state of the transmitted light to form interference fringes. Ordinary ray are energetic and extra ordinary ray are more energetic. Mathematically: ; where R= relative retardation in wavelength
C = optical constant; and = principle stresses EQUATION (1) is called "STRESS OPTICAL LAW" and is the basis of photoelasticity. Isochromatic fringes:
These are lines of constant principal stress difference, ( P – Q). "Photoelasticity can provide both magnitude and direction of principal stress and strain”
DEPARTMENT; MECHANICAL ENGG;
4RD SEMESTER, MECHANICAL
Isoclinic fringes.
It happens when principal stress direction coincides with the axis of polarization of the polarizer. The front figure shows appearance of isoclines in a beam during bending At 60°, 45°, 4 5°, and 30°. ORIENTATION Of the polarizer and analyzer with Respect to a Vertical datum.
DEPARTMENT; MECHANICAL ENGG;
4RD SEMESTER, MECHANICAL
Stress trajectories:
Isoclines in themselves do not provide a clear picture of direction of stresses in the model. However from them it i t is possible to construct a set of curves known as stress trajectories.
DEPARTMENT; MECHANICAL ENGG;
4RD SEMESTER, MECHANICAL
Basic Instrumentation for polarized light employed:
Basically three types that is a) Plane polarized, b) circular polarized and c) elliptical polarized
FRINGES IN CIRCULAR POLARISCOPE:
DEPARTMENT; MECHANICAL ENGG;
4RD SEMESTER, MECHANICAL
Figures are the fringe pattern for for a beam built in each end end and carrying a uniformly distributed load.Fig(A) represents whole order fringes and Fig(B) represents half order fringes
APPLICATIONS OF PHOTOELASTICIRTY:
Non-contact optical method for determining stresses and load paths in components or structures. Impact Testing Assembly Stress Analysis Glass Inspection Flaw Detection Residual Stress Analysis FEA Model Verification
PHOTOELASTIC MATERIALS:
DEPARTMENT; MECHANICAL ENGG;
4RD SEMESTER, MECHANICAL
Most widely used photoelastic material is an “epoxy -based -based resin known as ARALDITE, which is also termed a thermosetting resin”.
In U.S.A several well tried and successful materials for both two and three dimensional work namely “ BAKELITE, FOSTERITE AND KRISTON..” however these materials are rather expensive and show little advantage over ARALDITE.
Materials such as celluloid and Perspex , while exhibiting birefringence , are optically too insensitive for normal photoelastic use, although they are sometimes convenient when determining isoclines. REQUIREMENTS REQUIREMENTS FOR GOOD PHOTOELASTIC MATERIALS:
High optical sensitivity. Tensile strength and modulus. Absence of optical and mechanical creep Time edge stress Ability of casting and machining. Although photoelastic properties tend to vary somewhat from one batch of material to another, some typical values for various substances are given in the table below. substances
Tensile strength. (lbf/in2)
Modulus of elasticity (lbf/in2)
Poisson’s
ratio
Material fringe value, lbf/in2. per fringe for 1 in. λ = 5461 A
ARALDITE(U.K) 20 ºC 135 ºC
12000 300
0.45 * 10^6 0.0019 * 10^6
0.3 -
52 1.4
BAKELITE(U.S.A) 20ºC 110ºC
16000 400
0.62 * 10^6 0.0011 * 10^6
0.36 0.5
85 3.3
FOSTERITE(U.S.A) 87ºC
520
0.024 * 10^6
0.48
4
KRISTON(U.S.A) 20ºC 135ºC
8200 680
0.54 * 10^6 0.0138 * 10^6
-------
80 6.25
CELLULOSE NITRATE(U.K)
6000 TO 8000
0.25 * 10 ^6 TO 0.32 * 10^6
0.34
220
GELATINE(14% GLYCERINE)
----
14
0.5
0.17
DEPARTMENT; MECHANICAL ENGG;
4RD SEMESTER, MECHANICAL
PRODUCTS: GFP2000 for real-time photoelasticity. o KEY FEATURES
SYSTEM PERFORMENCE
DEPARTMENT; MECHANICAL ENGG;
4RD SEMESTER, MECHANICAL
LIMITATION: Data Acquisition for principal stress magnitude and direction Coating material and process for damp concrete-problem from bond
failure and unknown shrinkage stress effects in concrete The difference between thermal coefficient in coating material and concrete leads to errors to field investigation Too sensitive to the Young Modulus and poison's ratio ( local effect from coating process).
CONCLUSION: Photoelasticity theory and its application are given. The examples of products from venders are described. The most practical use of photoelasticity is to qualitatively investigate the stress-strain stress -strain pattern in complex specimen. The limitations of this technology is to measure the direction and magnitude of principal stress of a number of interesting locations is impractical due to the data acquisition process. The unreliability in applying the coating material in the field investigation of reinforced concrete structures due to shrinkage, thermal effect, bond, and local effect of material properties.
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DEPARTMENT; MECHANICAL ENGG;
