SolidWorks Skateboard Deck

Term 2, Week 4

This week i will be working on my mould. I can hopefully catch up with everyone else because i was away when everyone started thier moulds. Next time if we go into the computer labs i think we will either be working on our blogs (as usual) or working on our solid works program thingy. We're making speakers on it right now but after we've done that we will start making a longboard on it.

But for now i'll continue making my moulds and when i finish it i can start my longboard!!!

Research; Fiberglass, Tensile Strength, Ductility, Hardness, Shear Strength

Fiberglass
Fiberglass is material made from extremely fine fibers of glass. It is used as a reinforcing agent for many polymer products; the resulting composite material, properly known as fiber-reinforced polymer (FRP) or glass-reinforced plastic (GRP), is called "fiberglass" in popular usage. Glassmakers throughout history have experimented with glass fibers, but mass manufacture of fiberglass was only made possible with the invention of finer machine tooling. In 1893, Edward Drummond Libbey exhibited a dress at the World's Columbian Exposition incorporating glass fibers with the diameter and texture of silk fibers. This was first worn by the popular stage actress of the time Georgia Cayvan.
What is commonly known as "fiberglass" today, however, was invented in 1938 by Russell Games Slayter of Owens-Corning as a material to be used as insulation. It is marketed under the trade name Fiberglas, which has become a genericized trademark. A somewhat similar, but more expensive technology used for applications requiring very high strength and low weight is the use of carbon fiber.

Tensile Strength
The various definitions of tensile strength are shown in the following stress-strain graph for low-carbon steel:

Stress vs. Strain curve typical of structural steel:

1. Ultimate Strength
2. Yield Strength
3. Rupture
4. Strain hardening region
5. Necking region.
A: Apparent stress (F/A0)
B: Actual stress (F/A)


Metals including steel have a linear stress-strain relationship up to the yield point, as shown in the figure. In some steels the stress falls after the yield point. This is due to the interaction of carbon atoms and dislocations in the stressed steel. Cold worked and alloy steels do not show this effect. For most metals yield point is not sharply defined. Below the yield strength all deformation is recoverable, and the material will return to its initial shape when the load is removed. This recoverable deformation is known as elastic deformation. For stresses above the yield point the deformation is not recoverable, and the material will not return to its initial shape. This unrecoverable deformation is known as plastic deformation. For many applications plastic deformation is unacceptable, and the yield strength is used as the design limitation.
After the yield point, steel and many other ductile metals will undergo a period of strain hardening, in which the stress increases again with increasing strain up to the ultimate strength. If the material is unloaded at this point, the stress-strain curve will be parallel to that portion of the curve between the origin and the yield point. If it is re-loaded it will follow the unloading curve up again to the ultimate strength, which has become the new yield strength.
After a metal has been loaded to its yield strength it begins to "neck" as the cross-sectional area of the specimen decreases due to plastic flow. When necking becomes substantial, it may cause a reversal of the engineering stress-strain curve, where decreasing stress correlates to increasing strain because of geometric effects. This is because the engineering stress and engineering strain are calculated assuming the original cross-sectional area before necking. If the graph is plotted in terms of true stress and true strain the curve will always slope upwards and never reverse, as true stress is corrected for the decrease in cross-sectional area. Necking is not observed for materials loaded in compression. The peak stress on the engineering stress-strain curve is known as the ultimate strength. After a period of necking, the material will rupture and the stored elastic energy is released as noise and heat. The stress on the material at the time of rupture is known as the breaking strength.
Ductile metals do not have a well defined yield point. The yield strength is typically defined by the "0.2% offset strain". The yield strength at 0.2% offset is determined by finding the intersection of the stress-strain curve with a line parallel to the initial slope of the curve and which intercepts the abscissa at 0.2%. A stress-strain curve typical of aluminium along with the 0.2% offset line is shown in the figure below.

Ductility
Ductility is a mechanical property used to describe the extent to which materials can be deformed plastically without fracture.
In material science, ductility specifically refers to a material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar concept, refers to a material's ability to deform under compressive stress; this is often characterized by the material's ability to form a thin sheet by hammering or rolling. Ductility and malleability do not always correlate with each other; for instance, gold is both ductile and malleable, but lead is only malleable. Commonly, the term "ductility" is used to refer to both concepts, as they are very similar.

Hardness
Hardness is a characteristic of a solid material expressing its resistance to permanent deformation. Hardness can be measured on the Mohs scale or various other scales. Some of the other scales used for indentation hardness in engineering—Rockwell, Vickers, and Brinell—can be compared using practical conversion tables.
Hardness increases with decreasing particle size. This is known as the Hall-Petch relationship. However, below a critical grain-size, hardness decreases with decreasing grain size. This is known as the inverse Hall-Petch effect.
It is important to note that hardness of a material to deformation is dependent on its microdurability or small-scale shear modulus in any direction, not to any rigidity or stiffness properties such as its bulk modulus or Young's modulus. Scientists and journalists often confuse stiffness for hardness, and spuriously report materials that are not actually harder than diamond because the anisotropy of their solid cells compromise hardness in other dimensions, resulting in a material prone to spalling and flaking in squamose or acicular habits in that dimension (e.g., osmium is stiffer than diamond but only as hard as quartz). In other words, a claimed hard material should have similar hardness characteristics at any location on its surface.

Shear Strength
Shear strength in engineering is a term used to describe the strength of a material or component against the type of yield or structural failure where the material or component fails in shear.

In structural and mechanical engineering the shear strength of a component is important for designing the dimensions and materials to be used for the manufacture/construction of the component (e.g. beams, plates, or bolts) In a reinforced concrete beam, the main purpose of stirrups is to increase the shear strength.

For shear stress τ applies




where

σ1 is major principal stress
σ2 is minor principal stress

In general: ductile materials fail in shear (ex. aluminum), whereas brittle materials (ex. cast iron) fail in tension. See tensile strength.

To calculate: Given failing force and area, example-bolt shear strength:

Term 2, Week 3

I was away on monday so i missed out on our double period of DTM. If i were there i would've been working on my moulds some more for my longboard. But i missed out so i guess i'm doing it next DTM period on thursday. Today we're in the computer labs again to work on our blogs... Again.
But tomorrow we get to work on our moulds so i can catch up while everyone else is much further ahead of me.

Term 2, Week 2

On Monday, me, Jack and Will went down to Chafers to take our pictures of where we're going to skate when we finish our longboards. When we got back with our pictures we had to start our moulds. I don't actually know what to do but i've been getting help from around the class and stuff so i'll pick it up eventually.

This period we're just in the PC Labs again working on our blogs and i up-loaded the photos of where i'm going to be skating when i'm done with my longboard.

Skating Place

These are some pictures of where I'm going to try out my longboard when it's finished.