GLOSSARY
The glossary provides a list of terms used in this course with their definitions. The different terms can be opened by clicking on the term.
Anisotropic material
Material with mechanical properties depending on the direction.
Airframe
Structure that takes up all forces during operation of the vehicle.
Brittleness
Property of material that allows little bending or deformation without shattering.
Composites
Engineering materials containing two or more distinct and structurally complementary substances with different physical or chemical properties, having structural or functional properties not present in the individual substances.
Contraction/Expansion
Reaction produced in material as the result of heating or cooling.
Corrosion
In general: degradation of engineering materials due to chemical reaction with its environment.
Metal specific; electrochemical oxidation in reaction with an oxidant such as oxygen.
Damage tolerance
The ability of the structure to sustain anticipated loads in the presence of fatigue, corrosion or accidental damage until such damage is detected through inspections or malfunctions and is repaired.
Density
Weight of a unit volume of material
Ductility
Property of metal that allows it to be permanently drawn, bent, or twisted into various shapes without breaking.
Durability
The ability of the structure to sustain degradation from sources as fatigue, corrosion, accidental damage and environmental deterioration to the extent that they can be controlled by economically acceptable maintenance and inspection programs.
Elasticity
Property enables material to return to its original shape when the force which causes the change of shape is removed.
Engineering stress
Load divided by the original cross-section of the material or component.
Fail safe
Fail-safe is the attribute of the structure that permits it to retain required residual strength for a period of un-repaired use after failure or partial failure of a principal structural element.
Fatigue
Damage phenomenon induced by multiple load cycles below ultimate strength of material or structure causing permanent deterioration of material or structure resulting in a reduction in load bearing capability.
Fiber metal laminate
Composite material combining metal sheets and fiber reinforced composites.
Fracture toughness
Measure of energy needed to fail a specimen containing a crack.
Galvanic corrosion
Electrochemical process in which one metal corrodes when in electrical contact with a different type of metal or material and both metals are immersed in a substance containing electrolyte.
Geometrical tolerances
Maximum variation allowed in form or positioning.
Glass transition temperature
The temperature at which polymers exhibit a transition from a more glassy (hard/brittle) state to a rubbery (elastic/flexible) state.
Hardness
Ability to resist abrasion, penetration, cutting or permanent distortion.
Impact Toughness
Measure of energy needed to fracture a notched specimen.
Isotropic material
Material having identical mechanical properties in all directions.
Modulus of Elasticity or Young’s modulus \(\>\>E\)
Measure for material resistance against imposed Elastic deformation. The value of this Young’s modulus is a characteristic value for a material; a high value indicates a stiff material, a low value a flexible material
Normal stress
Stress that acts perpendicular to the surface of the material
\[ \sigma = \frac{F}{A}\] \[ \sigma = E \epsilon \]Normal strain
Normalized change in axial length of an object.
\[ \epsilon = \frac{\Delta L}{L} \]Orthotropic material
Material with properties that differ in all three directions.
Poisson’s ratio
The ratio between the transverse strain and the axial strain in a material.
Primary structural element
Critical load bearing structure of an aircraft or spacecraft that in case of severe damage will fail the entire aircraft/spacecraft.
Quasi-isotropic material
Approximation of isotropic material by placing multiple anisotropic layers in different directions.
Rule of mixtures
A simple first estimate of properties of a composite, based on the properties of its constituents: \[ \rho_{FRP}=\rho_F\frac{V_F}{V_{FRP}} + \rho_M\frac{V_M}{V_{FRP}} \]
RTM
Resin Transfer Moulding
Safe life
Safe-life of a structure is the number of flights, landings, or flight hours, during which there is a low probability that the strength will degrade below its design strength.
Saint Venant’s principle
Disturbances in the stress field remain limited to the direct neighbourhood of the location of disturbance.
Secondary structural element
Structural elements of an aircraft or spacecraft that carry only air and inertial loads generated on or in the secondary structure
Shear modulus \( \> \> G \)
Measure for material resistance against shear. It is related to the modulus of Elasticity: \[ G = \frac{E}{2(1 + \nu)} \]
Shear strain
Ratio of deformation of a material due to shear. It it the angle a square block deforms at when a parallel force is applied.
\[ \gamma = \tan{\theta} \]Shear stress
Stress that acts parallel along the surface of a material.
\[ \tau = \frac{F}{A} \> \> \> \tau = G \gamma \]Specific property
Material property divided by its density.
Stress concentration factor
Parameter describing the relation between the peak stress at the (blunt) notch root and the nominal (netto) stress in the cross-section.
Stress intensity factor
Parameter describing the severity (intensity) of stresses near the crack tip.
Thermoplastic
A thermoplastic is a plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.
Thermoset
A thermoset is a polymer that is irreversibly hardened by curing from a soft solid or viscous liquid prepolymer or resin.
Toughness
Resistance against fracture. Represented by the area under the stres-strain curve. Expressed in J/m3
True stress
Load divided by the actual cross-section of the material.
VARTM
Vacuum Assisted Resin Transfer Moulding
VI
Vacuum Infusion