The free electrons explain why metals are such good of electricity. Structure of Engineering Materials Crystalline: most solids, regular, repeating and densely packed Non- most liquids and gas, random and loosely packed%;. Crystal The atoms of the material are rangefinders in a regular and repeating way in which atoms or molecules are packed together in a material is called the structure of that material. 3 crystal structures 1 . Body-centered A typical such as the one at the centre has eight near neighbors. 2 elements that crystallize%h in this pattern are iron and sodium.
Metals with BCC structures are strong such as iron (Fee). 2. Face-centered cubicles;if A typical atom in this type of crystals;* has 12 near neighbors. 2 elements that crystallize# in this pattern are copper” and aluminum. Metals with this structures are normally soft and ductile& because they are easy to 3. Hexagonal closed-packed*gits A typical in this type of crystal;;* also have 12 near neighbors. Elements that crystallize#;h in this pattern are zinc* and magnesium. Metals with this structures tend to be relatively brittle*.
Elasticity and Plasticity t is the property of a material that enables it to return to its original shape and size, after deformation as a result of the application of a stress. Plasticity¶ltВ±: it is the property&E of a material that allows it to be deformed without the ability to return to its original shape and size. Young 1 . Stress/Pressures/*j-J: it is defined as applied force (P) per unit cross sectional area. if;fife; (A) of the sample and normally measured as an/mm *Stress;if = Applied Load/Cross-sectional or N/mm. . Strength%J: it is defined as the ability to resist or excessive plastic under stress. 3. Strain*: It is defined as the ratio of change in to the original length of the member$-. 4. Young (E): E-value is a constant?M for a given material and is a measure of how a material is. It is defined as the ratio of (or stress&l) to (or compressive* *E-value = The greater the value of E, the more difficult it is to cause shortening or lengthening Of the material, I. E. Strong material. It does not deform easily. 5.
The formula (Hooked’ s law) *oh = E Where E = modulus of elasticity or Young modulus Typical Stress-strain Graph Factor of safety Factor of it is defined as the ratio between the yield stress*?; ND the allowable or working stressfez]. *Safety Factor = Yield Stress??EњJ/Allowable Stress;*њJ The allowable stress shall be less than yield stress The safety factor is usually between 1 and 2. Ductility Ductility-: it is the ability of a material to undergoВ± considerable amounted?3 of plastic before fractured. Fatigue it is long-term failure due to repetitive loading.
Failures may occur even when the maximum stress is less than the ultimate tensile Of the material. Trillium silicate’s?REF (CSS) Rapid strength gain and responsible for early strength. Trillium illuminate$;BE (CA) Quick setting (controlled by gypsum=) but susceptible% to caliphates; attack. Rapid-Hardening Portland Cement Obtained by increasing the CSS content Early strength development is considerably higher*E6 than that of OPAC, while long-term strength is similar. Application: 1. Permit-a* increased speed of construction 2.
Less risk of concrete in frostyR weather Accelerators Increases the rate of strength gain at an early age. Most common is calcium chloride(NCAA) but may corrode steel. Does not increase final strength. Facilitate early striping of also for repair ark where early setting is desirable¶J Air entraining admixtures Generates evenly air bubbles in the mix. Improves against*JAY from frost*’A and marine m. Also improves the workability and cohesiveness;;kit of the concrete. Retarding agents Reduces the rate of evolution?В± of heat. Necessary for very large concrete pour* A.
Necessary for concrete pour* A in hot weather to reduce any [email protected] existentialist of the concrete. Water reducing admixtures (Plasticizer)?XX?J Reduces the amount of water required for a given workability. Most common is calcium sultanate$B. Reduces the risk of evaporation Curing Curing?Ft is the prevention;if of loss of moisture’s from new concrete. Preventing moisture is particularly important if the water/ cement ratio is low, if the cement is rapid hardening, and if the concrete contains Pa or The curing should also maintain a satisfactory temperature and avoid the development of high temperature within the concrete.
Curing and protection should start immediately after the compaction’s of the concrete to protect it from: 1 . Premature drying out, particularly by solar radiation and wind; 2. Rain and flowing water; 3. Rapid cooling during the first few days after placing; 4. High internal thermal gradients; and 5. Vibration and which may disrupted the concrete and interfere*” with its bond to the reinforcement. Curing methods Common methods of curing are: 1 . Keep framework in 2. Cover the surface with an impermeable sheet¶¶J-E-I% of material such as polyethylene’s, which should be well sealed and fastened%SE; 3. He surface with an efficient curing membrane?f,; 4. Cover the surface with Hessian*Fife, sacking or similar absorbent and 5. Continuous or applications of water to the surface, avoiding alternate wetting and and the application of cold water to warm};n concrete surfaces. Workability Workability means how easy it is to place, handle, compact and finish a concrete Concrete that is dry may be difficult to handle, place, compact and finish, and, if not constructed will not be strong or durable when finally Workability is affected by: 1 .
Amount of cement (cement paste is liquid part of the concrete mix, I. E. The more paste mixed with the coarse*; and fine:gal. aggregates, the more workable a mix) 2. Water content (higher water content leads to higher workability) 3. Grading (uniform grading leads to better workability) 4. Admixture’s;LLC entraining agents) 5. Fineness of commencements (finer cement?eke, faster loss of workability) 6. Time (cement hydration*Ft) 7. Temperature (higher temperature leads to loss of workability) Workability methods To make a more workable mix Elfin*;?: 1 .
Add more cement paste 2. Use well graded;d aggregates 3. Use an admixture 4. Never try to make a more workable by just adding more water because this lowers the strength and of concrete. Compaction Compaction’s IS done by vibrating*j, the concrete which liquefies*?fee it, allowing the trapped?elf air to rise out. Concrete settles, all the space in the forms. Compaction must be done as concrete is placed, while it is still plastic. Compacted concrete is more strong and durable,?Suffix.
Honeycombing Honeycombing*8 occurs when voids are left in concrete due to failure? of the mortar-INN to effectively fill the spaces among the coarse aggregate Occurs due to poor compaction or lesser quantity of fine sand leading to a concrete mix. Carbon Content of Steels All steels contain carbon but the description}ii plain carbon steels;I?FWIW is used to distinguish%¶ those steels which do not contain substantial proportions*TTFN of alloying These are subdivided . Low carbon steel (up to 0. 15% carbon) is soft and suitable for iron wire and thin sheet for tin 2.
Mile steel (O. 15 to 0. 25% carbon) is strong, and suitable for rolling”; into sections, strip and sheet but not usually for They are easily worked and welded. The group includes normal and high strength low wieldable structural 3. Medium carbon steel (0. 2 to 0. 5% carbon) is suitable for forgings and for general engineering purposes. 4. High carbon steel (0. 5 to 1 % carbon): Tensile strength increases to about INN/ mm as the carbon content increase to about 1 % and this strength can be increased by heat treatment. Hardness increases up to about 1. % carbon content, but ductility’& decrease and high carbon steel is too brittle*h; for structural work. They are also difficult to It can be used as files and cutting tools. It is also suitable for casting%, e. G. Heavy machine Protection 1. Keep metal dry 2. Where cannot be avoided, impermeable I. E. Painting, will greatly reduce the likelihood of corrosion 3. Gallivanting?* of steel, in which a thin zinc coating is applied 4. Is often applied to articles such as nuts and 5. Catholic protection 6. Bituminous 7. Epoxy Fire proofing 1 . Encasement in . Enclosure in metal lath and 3.
Enclosure in multiple layers of gypsum boardingtiff$E. 4. Spray on fireproofing coating or Heat Treatment 1 . Annealing: heated metal to about ICC and then cooled it back to room temperature very slowly in the furnaces*. The result is a soft malleable steel of fairly yield pointњ*. 2. Normalizing: instead of cooling in furnace as described above;Q-Iiњ;if, the steel is taken out from the furnace and cooled in still The result is increased strength and impact 3. Quenching: heated metal to about ICC and then cooling it rapidly by palatinates hot metal into cold water.
The result is increased hardness and strength but also increased brittleness&i; Din. 4. Tempering: temperature used for tempering is 200-ICC and then permitted to cool in still air. The result is to restore'”* toughnessВ± to the steel without losing all the hardness&. Float Glass/Annealed The float process consists of taking the raw W, Soda Ash Lime pip%E?and other Oxides?Feb.) and heat to 1 5000. This molten;kill material then flow on to a shallow* of Ting, float and spread out” to form an even layer*if. The thickness* of the glass is controlled by the speed of the flow.
As the glass low along the tin bathing, the temperature drop to 5000 where the glass then passes thorough% the annealing chamber or to around 2500 and produces the polished parallel%-zip sheets of glass. It is relatively cheap and easily cut and form. This type of glass is without heat treatment. It is fragile;%if and breaks to sharp like edges” which can cause serious injuries%. Tempered In order to provide a larger strength? and to achieve the objective that breakage}A will not generate sharp piecewise*h for hurting human, an annealed glassiness’s% can be under a heat-treating*Fib process.
The moon process is to first cut the glass to the desired and then put inside a and heated uniformities! To 7000. Upon leaving the The glass is cooled rapidly with cold air blown?A on to both surface. This rapid set the two outer surfaces while]a; the internal core rearmament relatively*eq hot. The core then cooled naturallym;eD in consequence-RIG*R shrinking-NC? generating the compressive force”if inside with the ;o outer tensile surfaces%if. The forces generated in this process physically;E* pull the structure to create a glass sheet of 5 times the strengths;EGG of float glass.
The process is relatively lovef& and hence cheap to manufactured. On breaking, the stresses cause the glass to and fragment into?R disc of between 5-1 Mom depending on the of the glass. Cannot be worked on once formed either edge or will result in the glass Spontaneous Breakage%WHO 1 . One disadvantage for using tempered glass is the problem of spontaneous due to Nickel (Ins). The impurities exist in all glasses whether annealed;>k, [email protected]’R or heat strengthened*?fee. The quantity of impurities depends on the batch* of raw materials in which the glass is made.
This impurity Ins exists in two hysterical Alpha (unstable) and Beta (stable) in which Alpha given time will revert back to Beta with a slight increase*Fulfill in volume. Since rapid cooling and setting of outer layer create tensionsif as the center cool slower, this preshrinking;j] gives tempered glass its unique quality of up to 5 times that of float glass. But Alpha Ins particles are dimensionally unstable a fraction of a omicron* as it to Beta. For other glasses, the small amount of induced stresses?TX does not cause any problem.
In tempered glass, even minute expansion will imbalance the structure and the result spontaneous breakage$I?N. Ins forms a break pattern commonly known as the ‘butterfly wings’.