Term Paper

Strength of Material

MEC-201

D.O.S: 15/11/2010

TOPIC: Non-Destructive Testing for Non-Ferrous materials like Aluminium and Copper.

Submitted To: Submitted By:

Mr. Ashish K.G. Saran Sachin Rana

Dept. of Mechanical Engg. Rk4901 B35

Reg. no.:-10904976

ACKNOWLEDGEMENT

To many individuals I am indebted good counsel and assistance in

various ways in this respect one of my sincerest thanks to Mr. Ashish

Sir, Sir of Lovely Professional University, Phagwara, for their kind

cooperation and able guidance.

I owe a deep sense of ineptness of my pureness that has been source of

inspiration in every work of my life.

I deeply express our ineptness and thanks to all my faculty member and

friends for there in valuable, guidance which enable me to bring out this

project in a presentable manner.

CONTENT

Introduction

What is Non Destructive Testing?

Methods of NDT

Visual Liquid Penetrant Magnetic Ultrasonic Eddy Current

NDT for Aluminium and copper

References

Introduction

Nondestructive testing (NDT) has been defined as comprising those test methods used to examine an object, material or system without impairing its future usefulness. The term is generally applied to nonmedical investigations of material integrity.

Nondestructive testing is used to investigate the material integrity of the test object. A number of other technologies - for instance, radio astronomy, voltage and amperage measurement and rheometry (flow measurement) - are nondestructive but are not used to evaluate material properties specifically. Nondestructive testing is concerned in a practical way with the performance of the test piece - how long may the piece be used and when does it need to be checked again? Radar and sonar are classified as nondestructive testing when used to inspect dams, for instance, but not when they are used to chart a river bottom.

What is Non-Destructive Testing?

Nondestructive testing asks "Is there something wrong with this material?" Various performance and proof tests, in contrast, ask "Does this component work?" This is the reason that it is not considered nondestructive testing when an inspector checks a circuit by running electric current through it. Hydrostatic pressure testing is usually proof testing and intrinsically not nondestructive testing. Acoustic emission testing used to monitor changes in a pressure vessel's integrity during hydrostatic testing is nondestructive testing.

Another gray area that invites various interpretations in defining nondestructive testing is that of future usefulness. Some material investigations involve taking a sample of the inspected part for testing that is inherently destructive. A noncritical part of a pressure vessel may be scraped or shaved to get a sample for electron microscopy, for example. Although future usefulness of the vessel is not impaired by the loss of material, the procedure is inherently destructive and the shaving itself - in one sense the true "test object" - has been removed from service permanently.

The idea of future usefulness is relevant to the quality control practice of sampling. Sampling (that is, the use of less than 100 percent inspection to draw inferences about the unsampled lots) is nondestructive testing if the tested sample is returned to service. If the steel is tested to verify the alloy in some bolts that can then be returned to service, then the test is nondestructive. In contrast, even if spectroscopy used in the chemical testing of many fluids is inherently nondestructive, the process is destructive if the test samples are discarded after testing.

Methods of NDT

Visual Liquid Penetrant Magnetic

Ultrasonic Eddy Current

1.Visual Method:

The visual inspection is the basic and oldest non-destructive method for detection of surface defects on products, welds, components, and for the assessment of the condition of individual parts of various facilities. The visual inspection should always precede other non-destructive method, because it can reveal defects that can prevent correct performance or assessment of results of other non-destructive method. For the purpose of high quality performance of visual inspection it is necessary to know the construction of the inspected facility, technology of the production of the inspected product, types of defects and their causes of occurrence. The quality of visual inspection is based on long-time experiences of the worker who performs this inspection.

We can divide the visual inspection into direct and indirect inspection.

Direct visual inspection

This inspection can be performed only on places, where the operator can physically get into. The eyesight of the operator is used during this method, respectively simple aids can be used (magnifying glass, gauges, camera etc.).

Indirect visual inspection

Places that are inaccessible for the eye of the operator are inspected with endoscopes (fixed or flexible).

2.Liquid Penetrant:

The penetrant materials used today are much more sophisticated than the kerosene and whiting first used by railroad inspectors near the turn of the 20th century.  Today's penetrants are carefully formulated to produce the level of sensitivity desired by the inspector.  To perform well, a penetrant must possess a number of important characteristics. A penetrant must:

spread easily over the surface of the material being inspected to provide complete and even coverage.

be drawn into surface breaking defects by capillary action. remain in the defect but remove easily from the surface of the part. remain fluid so it can be drawn back to the surface of the part through the drying and

developing steps. be highly visible or fluoresce brightly to produce easy to see indications. not be harmful to the material being tested or the inspector.

All penetrant materials do not perform the same and are not designed to perform the same. Penetrant manufactures have developed different formulations to address a variety of inspection applications.   Some applications call for the detection of the smallest defects possible and have smooth surfaces where the penetrant is easy to remove.  In other applications, the rejectable defect size may be larger and a penetrant formulated to find larger flaws can be used.  The penetrants that are used to detect the smallest defect will also produce the largest amount of irrelevant indications.

Penetrant materials are classified in the various industry and government specifications by their physical characteristics and their performance. Aerospace Material Specification (AMS) 2644, Inspection Material, Penetrant, is now the primary specification used in the USA to control penetrant materials.  Historically, Military Standard 25135, Inspection Materials, Penetrants, has been the primary document for specifying penetrants but this document is slowly being phased out and replaced by AMS 2644.  Other specifications such as ASTM 1417, Standard Practice for Liquid Penetrant Examinations, may also contain information on the classification of penetrant materials but they are generally referred back to MIL-I-25135 or AMS 2644.

Penetrant materials come in two basic types. These types are listed below:

Type 1 - Fluorescent Penetrants Type 2 - Visible Penetrants

Fluorescent penetrants contain a dye or several dyes that fluoresce when exposed to ultraviolet radiation.  Visible penetrants contain a red dye that provides high contrast against the white developer background. Fluorescent penetrant systems are more sensitive than visible penetrant systems because the eye is drawn to the glow of the fluorescing indication.  However, visible penetrants do not require a darkened area and an ultraviolet light in order to make an inspection. Visible penetrants are also less vulnerable to contamination from things such as cleaning fluid that can significantly reduce the strength of a fluorescent indication.

3.Magnetic Method:

This NDT method is accomplished by inducing a magnetic field in a ferromagnetic material and then dusting the surface with iron particles (either dry or suspended in liquid). Surface and near-surface flaws disrupt the flow of the magnetic field within the part and force some of the field to leak out at the surface. Iron particles are attracted and concentrated at sites of the magnetic flux leakages. This produces a visible indication of defect on the surface of the material.  The images above demonstrate a component before and after inspection using dry magnetic particles.

4.Ultrasonic Method:

In ultrasonic testing, high-frequency sound waves are transmitted into a material to detect imperfections or to locate changes in material properties. The most commonly used ultrasonic testing technique is pulse echo, whereby sound is introduced into a test object and reflections (echoes) from internal imperfections or the part's geometrical surfaces are returned to a receiver. Below is an example of shear wave weld inspection. Notice the indication extending to the upper limits of the screen. This indication is produced by sound reflected from a defect within the weld.

5.Eddy Current Method:

There are a number of electromagnetic testing methods but the focus here will be on eddy current testing. In eddy current testing, electrical currents (eddy currents) are generated in a conductive material by a changing magnetic field. The strength of these eddy currents can be measured. Material defects cause interruptions in the flow of the eddy currents which alert the inspector to the presence of a defect or other change in the material. Eddy currents are also affected by the electrical conductivity and magnetic permeability of a material, which makes it possible to sort some materials based on these properties. The technician in the image is inspecting an aircraft wing for defects.

NDT for Al and Cu

This invention relates to a method of non-destructively testing aluminum-to-copper welds and, more particularly, to a method of performing such testing by acoustic emission techniques.

When aluminum and copper parts are flash butt welded together, small quantities of relatively brittle copper-aluminum intermetallic compounds are usually formed at the joint interface. The quality of the weld depends to a large extent upon the thickness and dispersion of this deposit of intermetallic compounds. If this deposit is in the form of a continuous and relatively thick layer, the joint will be embrittled to such an extent that it may not be reliable under actual working conditions.

Heretofore, such joints have typically been tested by subjecting representative samples to a destructive bend test, referred to hereinafter as a 90°-180° bend test. In this bend test, a sample, in the form of a bar comprising copper and aluminum sections joined together by such a weld, is first bent at the weld joint until one section is angularly displaced by 90° from the other and is then reversely bent until said one section is at 180° to its previously-displaced position. If the sample can withstand such bending without significant debonding at the weld joint (e.g., less than 30% debonding), the weld is considered to have passed the test. But if significant debonding (i.e., 30 percent or more) does occur, a failure is indicated.

This bend test reveals much information on the thickness and distribution of the intermetallic compounds at the interface. Also, extensive testing has given a good correlation between bond test sampling and the reliability of similar welds throughout the anticipated lifetime of identical bars made in the same way as the tested bar.

But the destructive nature of the 90°-180° bend test is a definite disadvantage. The test specimen is rendered unusable by such test, and any bar that is to be actually used in a working environment cannot be subjected to an actual bend test.

References

http://www.brighthub.com/engineering/mechanical/articles/66882.aspx www.ndt.net/ www.ndt-ed.org/GeneralResources/IntroToNDT/Intro_to_NDT.ppt www.ndt-ed.org/.../IntroToNDT/GenIntroNDT.htm