Ship Stresses Flashcards
Define Stress
The load or force per unit area
Explain Strain
The distortion due to stress
Explain Tensile
Tending to increase the objects length
Explain Compression
Tending to decrease the objects length
Explain Shearing
Two forces acting in the opposite direction
Explain Static Force
Due to the difference in weight and support which occur throughout the ship
Explain Dynamic Forces
Created by the hammering of the water on the ship, the passage of waves along the ship and by moving machinery parts
Name The Types Of Longotiudinal Stresses
Sagging, hogging, alternate hatch loading
Name The Types Of Transverse Stresses
Wing loading
Which Stresses are Neither Longitudinal Or Transverse
Static water pressure, Drydock
Brittleness
When a material fractures under stress
Ductility
The ability of a material to be drawn or plastically deformed without fracture
Elasticity
A material that is able to regain its original size and shape after a deforming forces has been removed
Plasticity
The ability of a solid material to undergo permanent deformation, a non-reversable change of shape in response to an applied force
Strength
AKA mechanics of materials, is focused on analysing stresses and deflections in materials under load
Malleability
A physical property of metals that defines their ability to be hammered, pressed or rolled into thin sheets without breaking
Steel
Can be considered an a;;oy of iron and carbon
High Tensile Steel (HTS)
Use of higher strength steels allows reduction in thickness of deck, bottom shell and framing where it is fitted; the mid-ship section of larger vessels
List the Properties of Steel
- Reasonable cost
- Easily welded
- Ductility
- Homogeneity
- Yield point to be a higher proportion of ultimate tensile strength
- Chemical composition suitable for flame cutting without hardening
- Reasonable resistance to corrosion
Advantages of Aluminium and Alloy Aluminium
Lighter
Higher resistance to erosion
Not magnetic
Disadvantages of Aluminium and Alloy Aluminium
Expensive
Weak
Difficult to work
Poor fire resistance
Reacts badly with steel
Sandwich Plate System (SPS)
- A composite material comprised of two pieces of metal plates bonded with a polyurethane elastomer core, which transfers shear between each plate, and eliminating the need for stiffeners and precluding local faceplate buckling
- They are light, flat and stiff, with superior resistance to fatigue crack propagation, impact damage and local buckling
- They also provide built in fire insulation to international standards and very effective damping of ship borne noise and vibration
Glass Reinforced Plastic (GRP)
A composite material consisting of high strength glass fibres bonded together by a resin of a lower strength and as a result it exhibits the best characteristics of both materials
Properties of GRP
-Ease with which it can be moulded into complex shapes
-Strength
- Resistance to water
- Resistance to weathering
- High resistance to impact
- Doesn’t shatter
Timber
Used as a shock absorber on modern ships to protect steel decks as well as make them less slippy
Explain Safe Working Load (SWL)
Sometimes stated as the Normal Working Load (NWL), it is the maximum safe force a piece of lifting equipment can operate with, without fear of breaking. Usually marked on the equipment by the manufacturer
Explain Still water Sagging
If a vessel is supported at each end, then the middle will tend to sag. Cargo loaded midships will cause the vessel to sag
Explain Still Water Hogging
If the vessel is supported in the middle then the ends will sag (hogging). Cargo loaded in the for and aft of the hold caused the vessel to hog
Explain Alternate Hatch Loading
Maximum values of sheer forces occur where there are abrupt changes of weight - e.g. bulkhead between an empty and full compartment
Explain Wing Loading
When a ship is subject to a twisting moment
Explain Static Water Pressure
Pressure increases with depth so, the greater the pressure on the ship’s side and bottom plating. The tendency is for the sides to be pushed inwards, and the bottom to be pushed upwards
Explain Dry Docking
A ship is designed to withstand pressure from the outside. When the ship is in the dry dock this pressure is removed. The only things holding the ship are keel blocks, the billage blocks and the side shores
Explain Seaway Sagging
Due to the wave crest being at the for and aft of the vessel, the midship is un supported and tends to sag
Explain Seaway Hogging
Due to the wave crest raising the midship, the for and aft of the ship is unsupported and tends to sag
Explain Racking
Due to the rolling of the vessel, the waterline is not always horizontal. This means that the centre of buoyancy and centre of gravity are often not on the same line and push the transverse section into a diamond shape
Explain Panting
This is the “in and out” movement of the ship’s plating at the bow and stern areas due to the changing water pressures as the ship is sailing
Explain Pounding
This is the slamming down of the ship’s bottom plating near the bow during excessive pitching (falling heavily) in heavy weather
Main Materials used for Ship Building
Steel
Aluminium and Titanium alloy
Copper alloys
Glass
Cements
Foam
Brass
Wood
Name the Three Types of Welding
Fusion Welding
Gas Welding
Electric Arc Welding
What Type of Welding is This
Submerged arc welding
What Type of Welding is This
Tungsten Inert Gas Welding (TIG)
What Type of Welding is This
Metal Inert Gas Welding (MIG)
