Hot Working Cold Working No properties are strengthened during hot working of materials. The intention behind hot working of materials is to eliminate any imperfections: these can include closing gas pores and reducing composition differences. In addition, through hot rolling you can achieve anisotropic behaviour.
This means that the surface of the material will have a high surface finish. Ideally, brass would require this kind of treatment in order to improve its overall appearance; brass can be used for instruments and plating jewellery, so its appearances is arguably an important property. Cold working can have an effect on various properties of materials. These include dislocations moving through the metal structure. The metal becomes less malleable and ductile, while the tensile strength and hardness is increased. In terms of 60/40 and 70/30 brass, these properties would be impacted similarly, as the materials structural make up is relatively similar.
A downside to cold rolling of brass is that it may cause cracking, which has a detrimental effect of the materials appearance. This is why brass is generally hot worked. ii) The ability of a polymer tosustain a mechanical load depends on the strength of covalent bonds and theforces between the molecules. However, if a substantial fraction of the polymerchains can be aligned in the load-bearing direction, a larger portion of theload can be transmitted to the main-chain covalent bonds. This means that thefibres must be as strong as possible in order to sustain their loads. Polymerchains are oriented by subjecting them to extensional strain (flow) in themelt, which occurs to some extent in most thermoplastic fabrication methods.
Significantly more orientation can be induced by mechanically drawing a fibreas it leaves the die and just before it solidifies — thus freezing-in extendedchain conformations. This leads to uniaxial orientation in the draw direction.An example is shown schematically underneath. iii) Uni- and biaxial Stretching of various polymer films has been studied underwell-defined conditions of temperature and elongational strain rate in order todetermine the relationship between stress and recoverable strain for both modesof deformation.
The extent of molecular orientation has been investigated withthe aid of stress optical methods: In amorphous polymers birefringence was foundto be directly proportional to the frozen-in internal entropic stressirrespective of the latter’s relationship with recoverable strain. In a firstapproximation, molecular orientation can be understood in terms of deformationof a rubberlike network with temporary junction points. The total internalstress in an oriented glassy polymer may be significantly larger than theentropic stress. Experimental methods based on retractive force measurements,able to distinguish between internal stresses of different nature, aredescribed. In uni- and biaxially drawn films of polyethylene terephtalatepreferred planar orientation of (100) planes has been studied by means of X-raydiffraction and measurement of the three principal refractive indices. Theintrinsic birefringence of completely oriented PET films has been estimatedfrom these measurements with the aid of the Lorentz-Lorenz theory. The effectof draw ratio and temperature on the rate of crystallization and itsconsequences (increase of stretching stress and density, decrease of shrinkage)has also been studied.
Finally, the effect of molecular orientation on variousmechanical properties: modulus, tensile strength, impact resistance, creepcompliance, is discussed for both amorphous and semicrystalline polymers, withspecial emphasis on the predominant influence of amorphous phase orientation.iv) Generally, clay has a water content between 19.5 and 22.5%. The slightestdifference in water content (around 1%) can have a dramatic effect on the claysproperties: the clay can become either more malleable or stiffer as a result ofa loss/ increase in water content. Depending on what the clay is to be intendedto be used for, the water content should be decided prior to its use in anyform of manufacturing process.
Some clay may be used in structures, such asflood barriers. This would of course require it to be a sturdy, non-malleableform of clay i.e. a lower percentage of water content present in the material. v) Concrete is used on a regular basis in various structures, such asmotorways, so they have to be able to support large volumes of weight andtension across long periods of time. This means making the concrete strongerduring its processing. This can be achieved by the addition of more solid materialsinto the mixture, making it more sturdy once constructed.
These materials mayinclude large stones. Another way to make concrete stronger is usingreinforcement techniques. This can include positioning steel beams in thematerial, making it ideal for structures such as motorway bridges or factorybuildings.
vi) Smart materials are designed materials that have one or more properties that can besignificantly changed in a controlled fashion by external stimuli, such asstress, temperature, moisture, pH, electric or magnetic fields. This means that these materials can be usedfor a number of applications. One example of this could be water proof paint oncars: a primer base coat and clear coat provide protection for a carsprofessional finish from weather. If the correct properties that are requiredwere not present in the various layers of paint, the car would not be resistantto weather. Another example could be when heat is applied to fire sprinklers; alatch is released causing the sprinklers to activate. Moreover, piezoelectricmaterials can be used in children’s shoes: the impact in the sole causes asmall electric current to be produced, resulting in a sudden flash of light.Task 2 (M1)Steel alloy has many usesand contains other materials, such as iron.
Low carbon steels generally contain less than0.25% carbon and cannot be strengthened by heat-treating (strengthening canonly be accomplished through cold working). The low carbon material isrelatively soft and weak, but has extremely good ductility and toughness. Inaddition, it is machineable, weld-able, and is relatively inexpensive to produce.Moreover, Medium carbon steelshave carbon concentrations between 0.25% and 0.60%.
These steels may beheat-treated by quenching, and then tempering to improve their mechanicalproperties. On a strength-to-cost basis, the heat-treated medium carbon steelsprovide tremendous load carrying ability.In addition, aluminum alloys contain magnesium, which has a light weight and dense structure. Thismakes is a good material to use when constructing in the BIW stages ofmanufacturing. This is one of the most effective and widely used alloyingelements for aluminum.
Alloys in this series possess moderate to highstrength characteristics, as well as good weldablility and resistance tocorrosion in the marine environment. This differs from steel, as its alloycontains iron; this means that under the wrong weather conditions, steel has atendency to rust. Overall I would say that aluminium alloy is the bettermaterial to use for constructing a car’s body work and/ or chassis.