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Properties of Penetrant Materials((Group Members) (1)Logarajan Muthaliar…
Properties of Penetrant Materials((Group Members) (1)Logarajan Muthaliar a/l Ramasamy 134320 (2) Viisnu Prasath a/l Ratakrishnan 134339 (3) Samuel Edmund Theivendran (134331)
Surface Tension
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at liquid-solid interface, molecules of liquid have stronger attraction forces to the molecules of solid, wetting of surface occurs because adhesive forces are stronger
if mollecules of liquids have stronger attraction forces between each other than to the molecules of solid, cohesive forces are stronger, hence no wetting occurs
Wetting Ability
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surface tension / surface energy across an interface = energy required to form a unit area of new surface at interface
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In Liquid Penetrant Testing, three surface interfaces are involved
- solid-gas interface
- liquid-gas interface
- solid-liquid interface
Two conditions for ideal wettability:
- surface energy of solid-gas interface > liquid-gas interface + solid-liquid interface
2.surface energy solid-gas interface >> solid-liquid interface
Capillary Driving Force
is a function of the surface tension of the liquid-gas interface, the contact angle, and the size of the defect opening.
Force=2πrσcosθ
where, r=radius of the opening , σ = surface tension of liquid -gas interface and θ = contact angle
Capillary Pressure
Pressure, P is the force, F over a given area, A
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The penetrant will flow into the flaws continuously until an opposing force of trapped gas in the voids equals the driving force.
Specific Gravity
Is defined as the density of the penetrant materials to the density of the reference materials which normally water.
Gravitational force and the position of the flaws in the sample plays a role in the determining strength of the driving force.
Gravitational force will be added with driving force if the flaws is going in the direction towards the earth. Gravitational force will be subtracted from driving force if the flaws going against the direction of the earth.
Viscosity
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Viscosity affects the wettability of liquid penetrants on the surface of the sample. High viscosity penetrants have larger cohesive force than adhesive force.
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