whether the Ultra-Sonic Inspection method that?

NDT is one of the many methods used to detect the presence of discontinuities (disabled) deep, surface defects, defects near the surface (sub-surface) of equipment made of metal or alloy. These defects can be cracks (crack), disability gases, penetration is not perfect. In the welding slag inclusions, and others. The working principle is to utilize ultrasonic examination of the wave propagation of ultra-sonic transmitter released by the work piece and then the wave behind it was captured by a receiver (receiver). Received waves can be measured, the intensity, time propagation or resonance caused. So in general ultra-sonic inspection is based on differences in the intensity of the received wave, the difference in the intensity and propagation time and the difference resonance. Ultra Sonic can be used for various examinations.

Among others: 
-Detecting the presence of defects in materials.
-Measure the thickness of the material.
-Studying the structure of the material.
-Evaluation of the manufacturing process.

System used in the examination:
Contact testing 
Tests carried out by directly attaching transducer specimen surface.
Immersion testing 
Examination carried out by dipping the specimen and the transducer into the water bath.

Things that affect the inspection process:
Surface 
On an uneven surface specimen reflection will occur on the surface, so the examination is less to get maximum results.
The shape and location of defects.
In examining the shape and location of defects in test specimens that will be very influential on the outcome disability checks because not all easily identified.

sumber : letheg

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How to make Liquid Penetrant Inspection

The examinations were used to detect surface defects on porous solids are not porous. Defects that occur may arise because the manufacturing process or because of fatigue (fatigue) on the object that has been in use long enough. Cracks in investigating the cracks on the surface, and can not detect defects in the surface or near surface. This method is very effective and efficient use in the examination without damage, while relatively less expensive. The detection of cracks in this way does not depend on the size, shape, material structure, composition, and direction of cracks. Because the liquid penetrant can seep into the test object. This absorption occurs because there is a capillary power (low surface tension). His usage is not limited to ferrous metals and non ferrous metals, but can also be used in ceramics, plastic, glass and other objects of powder metallurgical process.

The liquid penetrant process following the steps below:
-Prepare the surface, in the sense of specimen surface must be clean and dry.
-Penetration, sprays penetrant on the surface of the specimen and allowed to stand for about 10 minutes for penetrant to enter into the cracks.
-Cleaning, this is done with the wash penetrant from the surface of the specimen carefully, and tries to clean the same direction.
-Developer, the developer material is sprayed onto the specimen surface so as penetrant enters the cracks will be lifted to the surface.
-Inspection, the observation specimen after the spray penetrant and will appear on specimen defects or cracks. Checks can be carried out under sufficient light or using ultraviolet light.

sumber : letheg

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Magnetic particle inspection - for basic

A way of knowing the existence of cracks or defects that exist on the surface (surface or sub surface discontinuities) in ferromagnetic materials. The working principle of this test is based on the nature of ferromagnetic objects that will give the poles of a magnet if the object is in the magnetization, the magnetic pole that will cause the flow of the magnetic field from North Pole to South Pole. If there are defects in the test object such defects will cause a new magnetic field, if the defect is located perpendicular to the direction of the magnetic field.

The advantages of this method include:
-Can detect very small defects.
-Detecting defects on complex objects.
-To examine surface and subsurface defects.
Can check-ring-shaped objects and pipes.
-Portable.

Disadvantages of this method include:
-The object is examined only ferromagnetic objects.
-Requires an electrical current.
-For large test objects in great need of a yoke as well.

source : letheg

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Crystal Structure in General

Arrangement of atoms in solids can be expected if the inter-atomic known whether or not to have directional properties. The atoms in the belt by bonding lead (covalent bonds, permanent dipole) lined up in one particular rule to satisfy the valence angle. If the bond was not the bonding lead (metal bonding, ionic bonding, Van der Waals bonds), the atoms behave like a ball and form a rigid structure to follow a specific geometric shapes are determined by comparison of their relative dimensions. In the crystalline inorganic compound complex nature of the bonds between the atoms can not be seen clearly his trademark, between covalent and ionic bonds. Furthermore, in some cases different types of bonding can work on single crystals. In this regard it should be noted that the various crystal structures presented below are grouped by main force acting on its bonds.

1. No lead bonding and simple ionic bond
2. Directional bonding and simple cobalent structure
3. Mixed complex bounding cristal

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Mixed Complex Bonding Crystal

In the crystal complex, plays a variety of atoms and the bond is a bond mix in many ways. The crystal structure thus can be understood when considering that the crystal is composed of a combination of coordination polyhedron, in which small stuan of the cation is surrounded by several anions. One example is a silicate which is an important raw material for ceramics.

The basic structure of the silicate is tetrahedron (SiO4) 4 -. Si-O bonds in coordination tetrahedron meet both the directional covalent bonds as well as comparisons of the relative atomic radius. There are various types of silicate structures for a variety of ways such combinations may happen SiO4 tetrahedron or between tetrahedron SiO2 with other ions. Because the magnitude of charge on the ion Si4 + and low coordination number, tetrahedron SiO4, rarely associated with the angle with him and never associated with the field with him.

A silicate in which each tetrahedron not connected to the other is called ortosilikat. Included in this group are olivine (Mg, Fe11) 2, (SiO4), and garnet (Mg, Fe11, Mn, Ca) 3, (Cr, Al, Fe111) 2, (SiO4) 3. In olivine, the oxygen ions form a hexagonal arrangement of meetings that the structure was distorted, while the silicon ion occupies the eighth place in the hexagonal tetrahedral them.

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directional bonding and simple covalent structures

The number of adjacent atoms covalently bonded to specific atoms, in the limit by covalent valence of the atom. Covalent valence is usually small, most of the covalent structures of molecular crystals, in which covalent bonds are found only on the molecule in question, but the molecules themselves each is bound by the bond dipole, which is different from covalent bonds. Many organic compounds have this structure, but a lot of bonding structure entirely based on covalent bonding. In general, the structure has covalent bonds stronger than ionic bonding structure, and compound of this structure is more stable and stronger at high temperatures. The number of atoms in a volume less than in the structure of the meeting because of the directional bonding thus its density is lower.

Bond distance between atoms for covalent bond different from ionic bonding. This is called covalent bonding radius of the atoms, a little to the coordination and orthohedral tetrahedral, and form hybrid orbital are also changed.
Typical structure can be seen below:

Diamond structure 
Lighter elements in group IV such as diamond (C), Si, Ge, gray tin, etc., has a diamond structure. In this structure every atom is bound by its overlap with each other and the sp3 hybrid orbital connective tissue in the direction of the peak octahedron.

The structure of graphite 
Graphite is a crystalline polymorph of carbon. Carbon atoms form a covalent bond coating composition of the meeting, which was tied with weak pi bond. The upper layer of dense array of covalent bonds formed by sp2 hybrid orbital.

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