fracture toughness measurement testing
DESCRIPTION
This is a ppt which will give u a better understanding of fracture toughness of a material in short time. It also has great exposure to testing method that we do in our laboratory class in undergraduate courses. So good luck with slide.TRANSCRIPT
FRACTURE FRACTURE TOUGHNESS & TOUGHNESS & its MEASUREMENT its MEASUREMENT
JAVED ALAM10MT10015
What is fracture toughness?It is a property which describes the ability of a material with a crack to resist fracture.
The linear-elastic fracture toughness of a material is determined by Stress intensity factor(K) at which a thin crack in the material begins to grow, denoted by KIC
Plastic-elastic fracture toughness is denoted byJIC
Fracture toughness is a quantitative way of expressing a material’s resistance to brittle fracture when a crack is present.
*If a material has much fracture toughness it will probably undergo ductile fracture.
*Brittle fracture is very characteristic of materials with less fracture toughness.
Stress intensity factor (K):
It is used to predict the stress state near the tip of a crack caused by a remote load or residual stresses.
It depends on nominal stress, and crack geometry: K = f(, a); It also depends on the location of crack, magnitude and distribution of stresses
Fracture Toughness Fracture Toughness TestsTests
A test sample is fatigue loaded to extend the machined notch by a prescribed amount.A clip gage extensometer is placed at the mouth of crack to monitor displacement.
If a lower toughness level is achieved with a thicker sample, then the value obtained initially is not valid.
Type of Specimens for Fracture Toughness Tests
Clip Gage Clip Gage ExtensometerExtensometer
Experimental setup
The sample was Perspex
Group-2
Max. load= 85.11 N
Extension at break=6.98mm
Flexural Tests with Pre-cracked Specimens
For three point bending: (D = S/2) = KIC = Y.(3PS/2W2t).a
Y = 1.93-3.07(a/w)+13.66(a/w)2-23.98(a/w)3+25.22(a/w)4
Calculation of KIC
Width=10.88 mm, t=5.7mm , a(crack length)=4.46mm , S=44 mm
(a/w)=0.41Y=2.027
Now P= Pmax=85.11 N
Substituting the value of P:
KIC = 1.143 MPa · m1/2
Group-1
a= 4.7166
a/w = 0.414
Y=2.039
KIC = 1.086 MPa · m1/2
Group-3 Crack length=5.066mm
Group -4
KIC =1.231 MPa · m1/2
Crack length=6.05mm
Thank you