Engineer's
Handbook
 
Reference Tables
 
Rapid
Prototyping
 
Manufacturing
Methods
 
Engineering
Materials
 
Engineering
Software
 
Reference Books
 
Mechanical
Components


Manufacturing Processes - Radiography Testing


Non-Destructive Evaluation/Testing - NDE/NDT


Radiography Testing - (RT)

This technique involves the use of penetrating gamma or X-radiation to examine parts and products for imperfections. An X-ray machine or radioactive isotope is used as a source of radiation. Radiation is directed through a part and onto film or other media. The resulting shadowgraph shows the internal soundness of the part. Possible imperfections are indicated as density changes in the film in the same manner as an X-ray shows broken bones.

Radiographic applications fall into two distinct categories evaluation of material properties and evaluation of manufacturing and assembly properties. Material property evaluation includes the determination of composition, density, uniformity, and cell or particle size. Manufacturing and assembly property evaluation is normally concerned with dimensions, flaws (voids, inclusions, and cracks), bond integrity (welds, brazes, etc.), and verification of proper assembly of component pieces.

Computed Tomography - (CT)

Computed Tomography (CT) is a powerful nondestructive evaluation (NDE) technique for producing 2-D and 3-D cross-sectional images of an object from flat X-ray images. Characteristics of the internal structure of an object such as dimensions, shape, internal defects, and density are readily available from CT images.

Photon Induced Positron Annihilation (PIPA)
& Distributed Source Positron Annihilation (DSPA) –

Photon Induced Positron Annihilation (PIPA) involves penetrating materials with a photon beam. This process creates positrons, which are attracted to nano-sized defects in the material. Eventually, the positrons collide with electrons in the material and are annihilated, releasing energy in the form of gamma rays. The gamma ray energy spectrum creates a distinct and readable signature of the size, quantity and type of defects present in the material.

Distributed Source Positron Annihilation (DSPA) uses a positron source emitter to deposit positrons into the subject material. The process is similar to PIPA after the positrons are deposited and attracted to nano-sized defects in the material.

PIPA and DSPA technologies detect fatigue, embrittlement, and other forms of structural damage in materials at the atomic level, before cracks appear. PIPA and DSPA can also accurately determine the remaining life of various materials and are more precise than any other existing flaw detection technology on the market.

Neutron Radiography -

Neutron Radiography is an imaging technique which provides images similar to X-ray radiography. The difference between neutron and X-ray interaction mechanisms produce significantly different and often complementary information. While X-ray attenuation is directly dependent on atomic number, neutrons are efficiently attenuated by only a few specific elements. For example, organic materials or water are clearly visible in neutron radiographs because of their high hydrogen content, while many structural materials such as aluminium or steel are nearly transparent. At the present time, Neutron Radiography is one of the main NDT techniques able to satisfy the quality-control requirements of explosive devices used in aerospace and defense programs.

X-ray Diffraction (XRD) -


X-ray diffraction is a versatile, non-destructive technique that reveals detailed information about the chemical composition and crystallographic structure of natural and manufactured materials.

A crystal lattice is a regular three-dimensional distribution (cubic, rhombic, etc.) of atoms in space. These are arranged so that they form a series of parallel planes separated from one another by a distance d, which varies according to the nature of the material. For any crystal, planes exist in a number of different orientations - each with its own specific d-spacing.

When a monochromatic X-ray beam with wavelength lambda is projected onto a crystalline material at an angle theta, diffraction occurs only when the distance traveled by the rays reflected from successive planes differs by a complete number n of wavelengths.

By varying the angle theta, the Bragg's Law conditions are satisfied by different d-spacings in polycrystalline materials. Plotting the angular positions and intensities of the resultant diffracted peaks of radiation produces a pattern, which is characteristic of the sample. Where a mixture of different phases is present, the resultant diffractogram is formed by addition of the individual patterns.

Based on the principle of X-ray diffraction, a wealth of structural, physical and chemical information about the material investigated can be obtained. A host of application techniques for various material classes is available, each revealing its own specific details of the sample studied.

X-ray Fluorescence (XRF) -

X-ray fluorescence is a technique of chemical analysis. The technique involves aiming an X-ray beam at the surface of an object; this beam is about 2 mm in diameter.

The interaction of X-rays with an object causes secondary (fluorescent) X-rays to be generated. Each element present in the object produces X-rays with different energies. These X-rays can be detected and displayed as a spectrum of intensity against energy: the positions of the peaks identify which elements are present and the peak heights identify how much of each element is present.

This is often used by museum curators to study ancient objects because measurements are non-destructive and usually the whole object can be analyzed, rather than a sample removed from one.

 


 

Radiography Testing




Copyright © 2004 - 2006 -- EngineersHandbook.com

All Rights Reserved - Disclaimer
Contact Information
Privacy Policy