ACTSTRUCTS - QUIZ 1 Reviewer

statics and mechanics

Understanding _______ and ______________ is crucial for structural analysis and design.

Structural system

Any deformable solid body capable of carrying and transmitting loads.

Beams, plates, or shells

Components of structural systems

Bar elements

One-dimensional structural members that handle bending, shearing, torsional, and axial loads.

Axial rods (two-force members)

Bar element that carry only axial loads.

Trusses

Structures made of axial rods, used for their lightweight tension/compression transmission.

Plate elements

Two-dimensional extensions of bar elements.

Membranes

Plate elements that carry in-plane axial loads.

Shear panels

Plate elements that carry in-plane shearing loads; found in missile fins, wings, and tail surfaces.

Shell elements

Curved plate elements in space, like fuselages, building domes, or pressure vessels.

Beam

A structural member that carries bending moments, also resists longitudinal tension and compression.

Torque

Formed by shear stresses in a cross-section; causes twisting around the longitudinal axis through the shear center.

Stress

A material's internal resistance to deformation caused by external loads.

Strain

The degree of deformation in a material under load.

Tension

Stress resisting forces pulling apart (e.g., elevator control cable).

Compression

Stress resisting crushing forces (e.g., landing gear struts).

Torsion

Stress causing twisting (e.g., from engine torque).

Shear

Stress resisting layers sliding past each other (e.g., riveted plates, bolts).

Bending

Combination of compression (inner side) and tension (outer side) in a member.

Loads are classified by their causes, what are these?

surface, body, inertia, thermal.

Surface loads

Caused by surface contact (e.g., static and dynamic pressure).

Body loads

Volume-based forces (e.g., inertial, magnetic, gravitational).

Inertia loads

Caused by thrust, maneuvers, or gusts.

Load factor (g-force)

Describes acceleration-induced inertia loads.

Dynamic loads

Time-dependent loads.

Static loads

Time-independent loads.

Thermal loads

Caused by temperature changes on restrained structures.

Wing function

To pick up air loads and transmit them to the fuselage.

Wing structure

Acts as beams and torsion members; includes stringers, spars, and skin/webs.

Wing spar

Heavy Spanwise beams taking shear and bending; most stress is transferred to them.

I-beam spar

Includes top/bottom (caps) and a vertical section (web).

Fail-safe spar

Spar designed so if one member fails, another carries the load.

Safe life

Number of flights or hours before structure degrades.

Damage tolerance

Structure's ability to sustain degradation over time, managed by maintenance.

Wing rib

Planar structures placed chordwise; redistribute loads and hold the skin stringer to the designed contour shape.

Wing skin

Carries part of flight/ground loads in stressed-skin design.

Wet wing

Fuel stored inside sealed wing structure.

Honeycomb skin

Lightweight core laminated between thin outer skin sheets for strength.

Monospar wing

One main spanwise member with ribs for shape.

Multispar wing

More than one main longitudinal member.

Box-beam wing

Two spars with connecting bulkheads; common in large aircraft.

Full cantilever; Semicantilever; Wire braced biplane; Long struts braced with jury struts

Different types of wing attachment

Full cantilever wing

Internally supported without external bracing.

Semi-cantilever wing

Supported by one or two struts or wires.

External struts/wires

Help carry wing loads; often streamlined.

Jury struts

Subdue movement of long struts far from the fuselage.

Fuselage

Main structure housing payload, controls, passengers, engines, etc.

Truss fuselage

Rigid Framework of beams/struts with fabric or aluminum cover.

Monocoque fuselage

Relies on the strength of the skin to carry primary loads.

Semi-monocoque fuselage

a modification to address monocoque construction. Skin plus reinforcements (longerons and stringers) for added strength.

Longerons

Longitudinal members helping skin resist bending loads.

Stringers

Lighter and more numerous than longerons; support skin and resist shape deformation.

Advantages of semi-monocoque

Strength, rigidity, streamlined form, and damage tolerance.

Fuselage loads

Bending, torsion, aerodynamic, internal pressure, and severe landing

Nacelle

Streamlined pod housing engine and accessories.

Cowling

Detachable cover panels for engine access and airflow.

Cowl flaps

Movable parts controlling engine temperature.

Empennage

Aircraft tail section with stabilizers and control surfaces.

Tail cone

Lightly built, closes and stremlines aft end of fuselage.

Empennage construction

Uses spars, ribs, and skin similar to wings.

Spar

transmits overloads to fuselage

Landing gear

provides suspension during taxi, takeoff, and landing; absorbs impact and assists control.

Landing gear components

Shock absorber, axle, torque links, braces, actuators, wheels, tires.

Limit load

Maximum expected load in service.

Ultimate load

Limit load × safety factor (F.S.).

Safety factor (F.S.)

Ratio of ultimate load to limit load (typically 1.5 for aircraft).

Stress-strain diagram

Graph of stress vs. strain during tensile test.

Hooke's Law

Stress is proportional to strain in elastic range.

straight line

From the origin to the proportional limit, the stress-strain curve is a ________________.

Elastic limit

Maximum stress without permanent deformation.

Elastic range

From the origin to the elastic limit.

Plastic range

To the right of the elastic range.

Yielding

Slight stress increase above the elastic limit causes permanent deformation.

Yield stress (yield point)

The stress that causes yielding.

Plastic deformation

deformation during yield.

Perfectly plastic

Material continues to elongate without any increase in load after yield point.

Strain hardening

Material strengthens after yielding before ultimate stress.

Necking

Localized narrowing after ultimate stress before forming constriction or neck.

Engineering design zone

Within elastic range where material returns to original shape.

stress-strain diagram

Uses actual cross-sectional area and shows rising curve until fracture.

Allowable stress

Must not exceed proportional limit; may be based on yield stress or safety factor.