Test purpose
Energy releasing factor is defined as a material per unit area of energy for the crack extension to a fixed length.Test results is a description of laminate crack propagation difficulty level value.
According to different application, the measurement will be used in several different load types as follows:
- Model I: crack propagation
- Model II: the in-plane shear
- Mode III: torsion load lateral loads in the laminate
Usually determine the energy releasing factor, mode I mainly use the standard such as ISO, ASTM, EN test method.There is no mode III standard.
ASTM standard test method for comprehensive evaluation of mode I and II, the proportion of the two models are different.
I measured using DCB test apparatus for mode
- Usually adopt DCB mode by double cantilever beam () sample I energy releasing factor.
- Sample usually prefabricated crack in the in-plane direction, such as insert pieces of plastic in the process of gluing cause crack.
- Can be used by bonding specimen, hinge or to holding the special equipment of aperture test load.
- Experiment, through the displacement of the beam to determine the sample opening displacement, and through the specimen deformation correction.Through the experiment measured force - stroke integral curve can get fracture energy.In through the video record on the side of the specimen crack propagation.
- Operator gage surface cracks can be observed through a magnifying glass, to calculate the crack length by hand.In order to allow the crack length measurement has a better traceability, generally USES digital magnifying glass.In the process of test, the digital magnifying glass can track crack extension and video record measurement process and results.
- Record video and measured force - stroke curve perfectly synchronized, this means that after the test can verify, if necessary can correct them.
- According to different test standards, the need to adopt different ways of test sequence and assess.
- Test standard as follows:ISO 1502, 1-0005, ASTM D5528, AITM AITM 1-0053, Boeing 7273, CRAG BSS method 600, NASA RP ST 1092-5, ESIS TC 4, prEN 6033 (had withdrawn)
Model II - use SENB/ENF test device is measured
Model II energy releasing factor by bending test and the tension and compression tests of the notch specimen measured.
Standard measurement by bending test mode II energy releasing factor, bending test of in-plane shear stress can cause crack propagation.Sample is often called the SENB (unilateral incision bending) specimens, but also often referred to as ENF (side edge notch bending) specimens.Deflection of beam displacement (a stiffness correction) or displacement sensor located in the center of the sample determination.
Crack the characteristics of the starting point is to test the largest force value at that point.After the measurement, you need to sample in liquid nitrogen cooling and completely destroyed, to measure the fracture.
