Fatigue tests measure the resistance of materials to damage, strength loss and failure under the repeated application of load. Aerospace materials must withstand repeated loading for long periods of time, which is in the order of 15 000–20 000 flight hours for modern jet engine materials and anywhere from 80 000 to 120 000 h for… Continue reading Fatigue Test
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Drop-weight impact test
Fibre–polymer composites are susceptible to damage from impact events such as bird strike, dropped tools during aircraft maintenance, tarmac debris kicked-up by the wheels during take-off or landing, and large hail stones. Impact testing is performed at different impact energy levels to screen composite materials for damage resistance and damage tolerance. The most common and… Continue reading Drop-weight impact test
Fracture test
Fracture toughness is an engineering property that defines the resistance of a material against cracking. Tough materials require large amounts of energy to crack whereas low toughness materials have little resistance against cracking. For the materials used in aircraft structures, fracture toughness is just as important as other mechanical properties such as elastic modulus and… Continue reading Fracture test
Hardness test
Simply stated, hardness is the resistance of a material to permanent indentation. Hardness is not a precisely defined engineering property, such as elastic modulus or yield strength, but it is still widely used to describe the resistance of materials to plastic deformation. The hardness of ductile materials is related to their yield strength, and the… Continue reading Hardness test
Flexure test
The flexure test measures the mechanical properties of materials when subjected to bending load. A flat rectangular specimen is loaded at three or four points, as shown in Fig. 5.14. The load causes the specimen to flex, thus inducing a compressive strain on the concave side, tensile strain on the convex side, and shear along the mid-plane.… Continue reading Flexure test
Compression test
The compression test determines the mechanical properties of materials under crushing loads. There are many aircraft structures that carry compression loads, such as the undercarriage during take-off and landing or the upper wing surface during flight, and therefore the mechanical behaviour of their materials must be determined by compression testing. It is often assumed that… Continue reading Compression test
Tension test
Basics of the tension test The tension test is one of the most common and important methods for measuring the mechanical properties of materials. The tension test is popular because a large number of properties can be determined in a single test: elastic modulus, strength, ductility, and other properties. The test is also popular because it… Continue reading Tension test
Introduction
The selection of materials for aircraft structures and engines is assessed according to a multitude of parameters such as cost, ease of manufacture, weight and a host of other factors. Central to the selection of materials is their mechanical properties such as stiffness, strength, fatigue resistance and creep performance. The durability properties of structural and… Continue reading Introduction
Defects in crystal structures
A perfect crystal structure exists when all the atoms are arranged in order through the entire material. When this occurs the metal has extraordinarily high strength. However, the crystal structure is rarely perfect, and instead contains imperfections that reduce the strength. For instance, the theoretical strength of pure aluminium is about 4600 MPa whereas the actual… Continue reading Defects in crystal structures
Crystal structure of metals
The atoms in solid metals are arranged in an ordered and repeating lattice pattern called the crystal structure. A crystalline material consists of a regular array of atoms that is repeated over a long distance compared with the atomic size. A simple analogy is the stacking of oranges in a grocery store, with each orange… Continue reading Crystal structure of metals