2 Testing of Materials & 3 properties ect

j. Failure modes

A failure mode is a cause of failure or one possible way a system can fail. When a system has many potential ways of failing, it has multiple failure modes or competing risks. ... Failure Modes and Effects Analysis (FMEA) is methodology for analyzing causes of failures and understanding their frequency and impact.

Specify precautions and limitations associated with testing thin gauge, narrow strips of material.

Clad aluminum alloy sheets cannot be tested directly with any accuracy with a Rockwell hardness tester. If the hardness value of the base metal is desired, the pure aluminum coating must be removed from the area to be checked prior to testing.

b. yield point

In materials science and engineering, the yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Prior to the yield point, a material will deform elastically and will return to its original shape when the applied stress is removed.

Define the following terms relating to the properties and characteristics of aircraft materials and give examples of where each is a factor in aircraft design, construction and maintenance: a. Strength

One of the most important properties of a material is strength. Strength is the ability of a material to resist deformation. Strength is also the ability of a material to resist stress without breaking. The type of load or stress on the material affects the strength it exhibits. a metals strength is determined by the percentage of the parent metal and other elemtents used to make the alloy

c. percentage elongation

Percent elongation is one way to measure and quantify the ductility of a material. The material's final length is compared with its original length to determine the percent elongation and the material's ductility. Percent elongation may also be known as percentage elongation. Percent Elongation - The strain at fracture in tension, expressed as a percentage = ((final gage length - initial gage length)/ initial gage length) x 100. Percent elongation is a measure of ductility.

Describe the testing of aluminium to distinguish between annealed, cold-worked, heat treated and aged material.

The Barcol tester is a portable unit designed for testing aluminum alloys, copper, brass, or other relatively soft materials. [Figure 7-12] It should not be used on aircraft steels. Approximate range of the tester is 25 to 100 Brinell. Hardness testing is a method of determining the results of heat treatment, as well as the state of a metal prior to heat treatment. Since hardness values can be tied in with tensile strength values and, in part, with wear resistance. Hardness tests are a valuable check of heat-treat control and of material properties. Practically all hardness testing equipment now uses the resistance to penetration as a measure of hardness. Included among the better-known hardness testers are the Brinell and Rockwell, both of which are described and illustrated in this section. Also included is the Barcol tester, a popular portable-type hardness tester currently in use.

h. Fatigue strength

The fatigue limit, also known as the endurance limit or fatigue strength, is the stress level below which an infinite number of loading cycles can be applied to a material without causing fatigue failure. Ferrous alloys and titanium alloys have a distinct limit.

Explain tensile and compression testing of metals with particular regard to determining by calculation: a. ultimate tensile stress

Ultimate tensile strength, often shortened to tensile strength, ultimate strength, or within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking. measured in psi but seeing it may take several thousand psi the leeter k is used e.g. 70,000psi is 70 ksi

d. Young's modulus of elasticity

Young's modulus is a measure of the ability of a material to withstand changes in length when under lengthwise tension or compression. Sometimes referred to as the modulus of elasticity, Young's modulus is equal to the longitudinal stress divided by the strain.

g. Bearing strength

ability of a joint to withstand any form aof crushing or excessive compression.

f. Shear strength

ability to resist opposing forces.

b. Malleability

is the materials ability to be bent, formed and shaped without cracking or braking.considered the opposite to hardness

f. Density

mass per unit volume. used to compare the weight of various metals. the standard form is water. one cubic cm of water weighs 1 gram therefore has a density of 1. aluminium has a density of 2.7

Explain the following testing methods used to determine hardness of metals: a. Rockwell

measures the depth to whisch the penetration sinks into the material. to use thwe rockwel, tester the material must be cleaned and two opposite surfaces ground flat and parallel. all scratches must be polished out. the sample is then placed on the anvil of the tester and then raised up against the penetrator a 10 kg minor load is then applied and the machine is zeroed. a major load is then applied to the machine and the dial indicates the depth the penetrator sinks into the material. it is indicated in rockwell numbers in either the red or black scale.

State the shape of the point used to contact the test specimen in each tester.

rockwell = conical diamond 1/16 inch ball 1/8 inch ball brinnell = spherical

c. Ductility

the ability of a material to be drawn into a wire stock. extrusion or rods is called ductility. they are a prefered metal in aircraft construction as they ease of forming and resistance to failure under shock loads. often used in cowlingss fuse wing ribs spars and bulkheads

h. Fusibility

the ability of a metal to be joined by heating and melting.

e. Yield strength

the ability of a metal to resist deformation is called its yield strength

i. Conductivity

the ability to carry heat or electricity.

Define the following terms that relate to the characteristics and properties of metals used in aircraft or aircraft component construction: a. Hardness

the ability to resist cutting, penetrating or abrasion. the tensile strength to steel relates to this n=but this relationship is not common for all materials.

d. Elasticity

the metals ability to return to to its original shape after normal stretching and bending.

g. Brittleness

the metals tendency to break or shatter when exposed to and is ythe opposite to ductility and malleability. more apt to break or crack before it changes shape

Identify on the Rockwell scale the notation for a hard and soft material and how the Rockwell number is determined for a specimen under test.

there are 3 major loads 60 kg 100kg and 150 kg. the 2 most commonly used are the b scale for soft materials using the 1/16 inch ball and 100 kg load and the c scale for hard materials using the conical diamond and 150kg load

k. Thermal expansion

to expand when heated and shrink when cooled

e. Toughness

to resist taring or breaking when bent or stretched

b. Brinell

uses hydraulic force to impress a spherical penetration into the surface of sample. the amount of force is approximatly 3000 kilograms for steel and 500 kilograms of non ferrous metals. the force is hydraulically applied by a hand pump and read on a pressure gauge. when the sanple is removed from the tester the diameter of the impression is measured with a special calibreated microscope. this diameter is converted intop a brinell number by using a chart furnished with the tester