Som-2017ume4008.docx

NETAJI SUBHASH UNIVERSITY OF TECHNOLOGY Home assignment on: 1. Selection criteria of engineering materials. 2. Composite materials.

SUBMITTED BY: - PARSHANT ROLL NO.: - 2017UME4008 PAPER CODE: - MEC09 TITLE: - SCIENCE OF MATERIAL

Division of Manufacturing and Mechanical Engineering

CONTENTS COMPOSITE MATERIAL 1) General introduction 2) What are composites made of? 3) Classification of composite material 4) Geometry and orientation of fibre 5) Role and Selection of Fibers

SELECTION CRETERIA FOR ENGINEERING MATERIALS 1) Mechanical Strength 2) Stability 3) Ductility 4) Availability 5) Fabrication 6) Design 7) Resistance 8) Cost

In Earlier time people do not know about the materials, so when they found difficulties with the materials they made they are in faces the problems in many fields like the strength of the materials. ductility, flexibility, hardness, fatigue etc.

So they mix different materials and found out that the properties of the materials have been changed. so this mixing of materials in different or the same proportions is known as Composite Materials.

Wattle and daub are one of the oldest materials made by the man and it is 6000 years old. Wattle and daub is a composite material used for making walls. it is an important construction material and still, use in present time.

Wattle and daub in Wooden frame the best part of the composite material is that every individual material which is used to make the composite material retain their own properties.

our bone is a live example of natural composite material which is strong and rigid and even flexible to resist normal breaking load and stress.

1) What are composites made of? Composite Materials are also known as Fiber Reinforcement Polymer composites are made from a polymer matrix that is reinforced with an engineered, man-made or natural fiber reinforcing material. The matrix is always protect the fibers from environmental and external damage and transfers the load between the fibers. The fibers is also provide strength and stiffness to reinforce the matrix—and help it resist cracks and fractures.

Provides strength and stiffness load between fibers

Protects and transfers

Create a matter with attribute superior to either component alone If this is classifying by matrix then there are thermoplastic composites, short fiber thermoplastics, long fiber thermoplastics or long fiber-reinforced thermoplastics. There are many thermoset composite, including paper composite panels. Many advanced thermoset polymer matrix systems usually incorporate aramid fiber and carbon fiber in an epoxy resin matrix.

Plywood is used widely in constructions

High strained composite are also another type of very great performance composites made using fibre and shape memory polymers resigns as the matrix. since a shape memory, a polymer is used as the matrix these composites have the ability to be easily manipulated into various configurations and when they are heated above their critical temperature and show high strength and stiffness at a lower temperature

High Strain Composite Structures (HSC Structures) are a class of composite material structures designed to perform in a high deformation setting. A very high level of strained composite structures transition from one shape to another upon the application of external forces. A mono HSC Structured component is so designed as to transition between at least two, but often more, dramatically different shapes.one of the shape is design to function as a structure which can support external loads. A sandwich structured composites a special class of composite that is fabricated by attaching two thin but stiff skins to a lightweight but thick core. core material having a low strength but due to its higher thickness it provides the sandwich composite high bending stiffness with the low density of the material.

Composite sandwich structure used at Nasa for testing

2)

CLASSIFIACTION OF COMPOSITE MATERIALS

Composite material basically classified in two categories: (2.1) The first level of classification is usually made with respect to the matrix constituent. The majored composited class include Organic Matrix Composites (OMCs), Metal Matrix Composites (MMCs) and Ceramic Matrix Composites (CMCs). The name termed organic matrix composite is generally assumed to include two classes of composites, namely Polymer Matrix Composites (PMCs) and carbon matrix composites commonly referred to as carbon composites. (2.1.1) Organic Matrix Composites-------a) Polymer Metrix Composites b) Metal Matrix Composites c) Ceramic Matrix Materials a) PMC Polymer material can have processed easily because of having low weight and desirable mechanical properties Two kind of polymers are there: -Thermosets and thermoplastics -Thermoset having the quality like as a well-bonded three-dimensional molecular structure after curing. They decompose instead of melting on hardening. They change very less the basic composition of the resin is enough to alter the conditions suitably for curing and determine its other characteristics. They also can be retaining in a partial cured condition too over prolonged periods of time, rendering Thermosets very flexible. So, they are most suit as matrix bases for advance conditions fiber reinforced composites. Thermosets founded a wide range of applications in the chopped fiber composites form particularly when a premixed or molding compound with fibers of specific quality and aspect ratio happens to be the starting material as in polymer and phenolic polyamide resins.

-Thermoplastics have 1 or 2-dimensional molecular structure and they also tend to at an elevated temperature and show exaggerated melting point. Another advantage is that the process of softening at elevated temperatures can reversed to regain its properties during cooling, facilitating applications of conventional compress techniques to mound the compounds.

b) MMC MMC at present generating a wide interest in research part. fracture toughness, High strength, and stiffness are offered by metal matrices than those offered by their polymer counterparts. They can also withstand very high temperature in corrosive environment than polymer composites. Most of the metals and alloy could be used as matrices and they require reinforcement materials which need to be stable over a range of temperature and non-reactive too. But the guided aspect for the choice depend very importantly essentially on the matrix material. Most metals and alloys make good matrices. Al, Titanium and (mg) are the popular matrix metals currently in vogue, which are particularly useful for aircraft applications. If metaled matrix material have to offer very high strength, they require high modulus reinforcements. The strength to weight ratio of resulted composites can be higher than most alloys.

c) CMM Ceramics can be described as solid materials having very strong ionic bonding in general and in few cases covalent bonding. High melt points, excellent corrosion resistance, stability at elevated temperatures and high compressive strength, render ceramic base matrix material a good for application required a structural material that doesn’t give way at temperatures above 1500ºC. Nceramic matrices are the obvious choiced for highest temperature applications. When ceramics have a very high thermal expansion coeff. than reinforcement material, the resultant composite is very unlikely to be have a greater level of strength or power. In this cases, the composite will automatically have developed strength or quality with in the whole ceramic at the time when the material cooling and resulting in micro crack extend from fiber to fiber with in the matrix structure. Micro cracking can also have resulted in a composite with tensile strength very lower than that of the matrix structure.

(2.2) The second position of classification refer to the reinforcement form fiber reinforced composite, laminar composites and particulate composite. Fiber Reinforced composites can be also further divide into those that contain discontinuous and continuous fiber.

2.2.1) Classification Based on Reinforcements: - a) Fiber Reinforced Composites b) Laminar Composites c) Particulate Reinforced Composites a) FRC Fibers are the important class of reinforcements, as they satisfy the desired conditions and transfer strength to the matrix constituent influencing and enhancing their properties as desired. Fibers fall short of ideal performance due to several factors. The performance of a fiber composite is judged by its length, shape, orientation, and composition of the fibers and the mechanical properties of the matrix. Glass fibers are the earliest known fibers used to reinforce materials. Ceramic and metal fibers were subsequently found out and put to extensive use, to render composites stiffer more resistant to heat. The orientation of the fiber in the matrix is an indication of the strength of the composite and the strength is greatest along the longitudinal directional of fiber. This doesn’t mean the longitudinal fibers can take the same quantum of load irrespective of the direction in which it is applied. Optimum performance from longitudinal fibers can be obtained if the load is applied along its direction. The slightest shift in the angle of loading may drastically reduce the strength of the composite. Unidirectional loading is found in few structures and hence it is prudent to give a mix of orientations for fibers in composites particularly where the load is expected to be the heaviest.

FRC

Stress Curve

Short-length fibres incorporated by the open- or close-mould process are found to be less efficient, although the input costs are considerably lower than filament winding. Most fibres in use currently are solids which are easy to produce and handle, having a circular cross-section, although a few non-conventional shaped and hollow fibres show signs of capabilities that can improve the mechanical qualities of the composites. Given the fact that the vast difference in length and effective diameter of the fibre are assets to a fibre composite, it follows that greater strength in the fibre can be achieved by smaller diameters due to minimization or total elimination of surface of surface defects. After flat-thin filaments came into vogue, fibres rectangular cross sections have provided new options for applications in high strength structures. Owing to their shapes, these fibres provide perfect packing, while hollow fibres show better structural efficiency in composites that are desired for their stiffness and compressive strengths. In hollow fibres, the transverse compressive strength is lower than that of a solid fibre composite whenever the hollow portion is more than half the total fibre diameter. However, they are not easy to handle and fabricate. b) Laminar Composites Laminar composites are found in as many combinations as the materials. They can be described as the many layers bounded together. These may be several layer of two or more metal materials occurring alternately in a determined order more than once and their can be many layer as required for specific purpose. Powder metallurgical processes like roll bonding, hot pressing, diffusion bonding, brazing and so on can be employed for the fabrication of different alloys of sheet, foil, powder or sprayed materials. It is not possible to achieve high strength materials unlike the fibre version. But sheets and foils can be made isotropic in two dimensions more easily than fibres. Foils and sheets are also made to exhibit high percentages of which they are put. For instance, a strong sheet may use over 92% in laminar structure, while it is difficult to make fibres of such compositions. fibre laminates cannot over 75% strong fibres.

c) Particulate Reinforced Composites Micro structure of metal and ceramic composites material, which shows particles of only one phase going into other, are known as particle reinforced composite. Triangular, Square and rounded like shapes of reinforcement are known, but the dimension of all of their sides are observed to be more or very less equal. The volume and size concentration of the dispersion distinguish it from dispersion hard material. The dispersed size in particulate composite is of the order of a very few micron and volume concentration is greater than 30%. The difference btw particulate composite and dispersion strength ones is, thus oblivious. The processes used to strengthen each of them is also diff. The dispersed in the dispersion strengthen material reinforces the matrix alloy by arrest motion of dislocation and require large force to fracture the restriction created by dispersion. In particulate composite, the particle strengthens the system by the hydrostatic coercion pressure of fillers in matrices and by their hardness related to the matrix. 3-dimensional reinforcement in composites offers isotropic properties, because of the three systematic perpendicular planes. Since it isnot homogeneous, the material properties acquired sensitivity to the constituent property, as well as property and the geo. Metric shape of the array.

(3) Common Categories of Composite Materials based on fibre length: Based on the form of reinforcement, common composite materials can be classified as follows: 3.1) Fibres as the reinforcement (Fibrous Composites): a) Random fibre reinforcement composites

Short fibre reinforcement composite b) Continuous fibre (long fibre)

3.2) particles as the reinforcement (particulate composite)

3.3) Fillers as the reinforcement (Filler composites):

3.4) Flat flakes as the reinforcement (Flake composites):

(4) Geometry and orientation of fibre: 

Aligned The properties of aligned fiber-reinforced composite materials are highly anisotropic. The lengthwise tensile strength will be high whereas the transverse tensile strength can be much less than even the matrix tensile strength. It also depend on the properties of the fibers and the matrix, the interference bond between them, and the presence of voids.

There are 2 different geometries for aligned fibers: 1. Continuous & Aligned The fibers are very large than a critical length which is the minimum length necessary such that the entire load is transmitted from the matrix to the fibers. If some how they are shorter than this critical length, only some of the load is transmitted. Fiber length very larger than 15 times the critical length are considered optimal. They are align and continuously type of fibers give the most effective strengthening for fiber composites. 2. Discontinuous & Aligned The fibers are shorter than the critical length. So the result is discontinuous fibers are very less effective in strengthening the material,by the on other side their composite modulus and tensile strengths can approach 50-90% of their continuous and aligned counterparts. And they also very cheaper, faster and easier to fabricate into complicated shapes. 

Random This is also called discrete, (or chopped) fibers. The strength is not so higher than aligned fibers, however, the advantaged is that the material will be istropic and cheaper.



Woven The fibers are very woven into a fabricated way which is layered with the matrix material and to make a laminated structure.

So the orientation and the geometry of the fiber is very important factor regarded composite material because the shape and geometry of the should be perfect of the section of the material also.

(5) Role and Selection of Fibers: During the selection process we must focused on the properties of the materials which includes compatibilities with matrix materials, thermal stability, density, melting, temperature etc. The efficiency of discontinuously reinforced composites is dependent on tensile strength and density of reinforcing phases. The compatibility, density, chemical and thermal stability of the reinforcement with matrix material is important for material fabrication as well as end

application. The thermal discord strain between the matrix and reinforcement is an important parameter for composites used in thermal cycling application. It is a function of difference between the coefficients of thermal expansion of the matrix and reinforcement. The manufacturing process selected and the reinforcement affects the crystal structure. Also the properties of the reinforcement depend upon the types of structural composites. The role of the reinforcement is to strengthen and stiffen the composite through prevention of matrix deformation by mechanical restraint. This restraint is generally a function of the ratio of interparticles spacing to particle diameter. In continuous fibre reinforced Composites, the reinforcement is the principal load-bearing constituent. The metallic matrix serves to hold the reinforcing fibers together and transfer as well as distribute the load. Discontinuous fiber reinforced Composites display characteristics between those of continuous fiber and particulate reinforced composites. Typically, the addition of reinforcement increases the strength, stiffness and temperature capability while reducing the thermal expansion coefficient of the resulting MMC. When combined with a metallic matrix of higher density, the reinforcement also serves to reduce the density of the composite, thus enhancing properties such as specific strength.

Some examples: Cements A cement is a composite material composed of ceramic (hard, brittle) and metal (soft, ductile) materials. A cermet is ideally designed to have the optimal properties of both a ceramic, such as high temperature resistance and hardness, and those of a metal, such as the ability to undergo plastic deformation.

Vulcanised rubber Vulcanised rubber is processed by a process known as vulcanisation process involves mixing of natural rubber with additives such as sulfer and other additives.

SELECTION CRETERIA FOR ENGINEERING MATERIALS The quality, execution, life et cetera of a building material, all are influenced by the engineering material being used for gathering that thing. Subsequently it ends up essential to pick a sensible Engineering materials for a productive planning thing. For decision of proper materials for any engineering application/thing, following segments should be considered: 9) Mechanical Strength 10) Stability 11) Ductility 12) Availability 13) Fabrication 14) Design 15) Resistance 16) Cost

1) Mechanical Strength: Mechanical strength is the essential criteria for the determination of appropriate materials for any Engineering application/item. Mechanical strength is the capacity of materials to withstand with load or powers. Materials chose for any designing application, ought to have a suitable mechanical strength to be skilled to withstand with burdens or powers created in the structure of building item amid task. The Study of the strength of materials frequently alludes to different strategies for figuring the anxieties and strains in basic individuals, for example, pillars, segments, and shafts. The techniques utilized to anticipate the reaction of a structure under stacking and its vulnerability to different disappointment modes considers the properties of the materials, for example, its yield quality, extreme quality, Young's modulus, and Poisson's proportion; furthermore, the mechanical component's naturally visible properties (geometric properties, for example, its length, width, thickness, limit limitations and sudden changes in geometry, for example, openings are considered. Different type of Strength ----Yield strength is the most reduced pressure that delivers a permanent deformation in a material. In a few materials, similar to aluminum composites, the purpose of yielding is hard to recognize, along these lines it is normally characterized as the pressure required to cause 0.2% plastic strain. This is known as a 0.2% proof pressure.

----Compressive strength is the farthest point condition of compressive pressure that prompts disappointment in a material in the way of pliable disappointment (vast hypothetical yield) or fragile disappointment (break as the consequence of split spread or sliding along a powerless plane. ---- Tensile strength is a cutoff condition of tensile stress that prompts tractable tensile stress in the way of bendable tensile stress (yield as the primary phase of that tensile stress, some solidifying in the second stage and breakage after a conceivable "neck" development) or weak disappointment (sudden breaking in at least two pieces at a low pressure state). Rigidity can be cited as either evident pressure or building pressure, yet designing pressure is the most usually utilized. --- Fatigue strength is a proportion of the quality of a material or a segment under cyclic loading, and is normally more hard to evaluate than the static quality measures. Weakness quality is cited as pressure abundancy or stress extend. ---Impact strength is the limit of the material to withstand a suddenly applied load and is expressed in terms of energy.

2) Stability: Engineering materials with some physical and technical ability requires understanding and predictive capability of materials behaviour under varying external parameters, such as temperature and pressure. This immediately brings one face to face with the basic difficulty of making a connection between materials behaviour at a microscopic level, where understanding is to be sought, and macroscopic behaviour which needs to be predicted. Bridge the corresponding gap in length scales that separates the ends of this spectrum has been a goal intensely pursued by theoretical physicists, experimentalists, and metallurgists alike. Tradition vies, the search for methods to bridge the length scale gap and to gain the needed predictive capability of materials properties has been conducted largely on a trial and basic, guided by the skill of the metallurgist, large volumes of experimental data, and often ad hoc semi phenomenological models. This problem has persisted almost to this day, and it is only recently that significant changes have begun to take place. These difference have been brought about by a number of developments, some of long standing, others of more recent vintage.

Basic static response of a specimen under tension

----Elasticity is a property of a material to return to its previous shape after stress is released. In some materials, the relation between applied stress is directly proportional to the resulting strain (up to a certain limit), and a graph representing those two quantities is a straight line. The tangent(x) or slope of this line is known as Young's modulus, or the "modulus of elasticity." The modulus of elasticity can be used to determine the stress–strain relationship in the linearelastic portion of the stress–strain curve. The linear elastic area is either below the yield point, or if a yield point is not easily identified on the stress–strain plot it is defined to be between 0 and 0.2% strain, and is defined as the region of strain in which no yielding (permanent deformation) occur ----plastic deformation is the opp. of elastic deformatial and is repersent as unrecoverable strain. Plastic deformation can be gain after the release of the applied stress. Many materials in the linear-elastic category are usually capable of plastic deformation. Brittle materials, like ceramics, do not experience any plastic deformation and will fracture under relatively low strain, while ductile materials such as metallic, lead, or polymers will plastically deform much more before a fracture initiation.

3) Ductility: Ductility is the measure of a material's ability to undergo significant plastic deformation before rupture, which may be expressed as percent elongation or percent area reduction from a tensile test. Ductility is mainly important in metal working, as materials that break or shatter under stress cannot be manipulated using metal-forming processes such as hammering, rolling, drawing or extruding. Malleable materials can be made cold using stamping or pressing, whereas brittle materials may be thermoformed

Ductile-brittle transition temperature: The ductile and brittle transition temperature (DBTT), nil ductility temperature (NDT), or nil ductility transition temperature of a metal is the temperature at which the fracture energy passes below a predetermined value. Ductile and brittle transition temperature is important since, once a material is cooled below the DBTT, it has a much greater tendency to shatter on impact instead of bending or deforming. Let take an example of zamak 3 exhibits good ductility at room temperature but shatters when impacted at sub-zero temperatures. (DBTT) is a important to be consider in selecting materials that are subjected to mechanical stresses. A similar phenomenon, the glass transition temperature, occurs with glasses and polymers, although the mechanism is different in these amorphous materials. In some of the materials, the transition is sharper than others and typically requires a temperature-sensitive deformation mechanism. For example, in materials with a body-cantered cubic (bcc) lattice the DBTT is readily apparent, as the motion of screw dislocations is very temperature sensitive because the rearrangement of the movement of core prior to slip requires thermal activation. This can be problem for steels with a high ferrite content. This famously resulted in serious hull cracking in Liberty ships in colder waters during World War II, causing many sinking’s. D BTT can also be influenced by external factors such as neutron radiation, which leads to an increase in internal lattice defects and a corresponding decrease in ductility and increase in DBTT. The most precise method of measuring the DBTT of a material is by fracture testing. Basically four point bend testing at a range of temperatures is performed on pre-cracked bars of polished material. For experiment processed at higher temperatures, dislocation activity increases. At some temperature, dislocations shield the crack tip to such an extent that the applied deformation rate is not sufficient for the stress intensity at the crack-tip to reach the critical value for fracture. The temp. at whole thing this occurs is the ductile–brittle transition temperature. If experiment is performed at a higher strain rate, more dislocation shielding is required to prevent brittle fracture, and the transition temperature is raised.

4) Availability: Materials architects and acquiring specialists wind up baffled in attempting to get materials that have a set number of makers or a restricted creation volume. Such dissatisfaction can be especially high when a little measure of material is expected to complete work or supplant a fizzled piece. An advanced and extensive report regarding the matter is the second version of the exemplary CORROSION BASICS course book. A few passages of that report are utilized here. ---Industry Dynamics: Metals organizations are experiencing what must be portrayed as twisting change. The aggressive scene is drastically changing on account of the accompanying drivers -Industry combination -Globalization -Over limit -Value disintegration ---Best Practices: The industry pioneers are transforming difficulties into upper hand and looking for zones where innovation can convey required enhancements. ---Overseeing more mind boggling supply chains: More unpredictable supply chains are rising as a result of the business combination. Chances to profit include: bring down costs, quicker reaction to clients, adaptable item sourcing and more proficient appropriation techniques. ---Uniting unique frameworks: Metals organizations have manufactured refined data frameworks to help their tasks. The evident qualities of the current framework can be utilized while getting control over expenses and multifaceted nature. New plans of action that settle on choices about clients and providers basic and as compelling are currently conceivable. --- Expediting order processing: Understanding client needs while overseeing metallurgical and process abilities decreases generally speaking preparing time, a key component toward picking up piece of the overall industry.

---Creative business forms: Redefining production network systems to expand effectiveness and embracing new business procedures, for example, work to-stock/complete to-arrange permits metals organizations to accomplish to a great degree focused lead times.

---Consolidating MRO spending: As an advantage escalated industry, keeping costly offices running is basic. Tending to the test of augmenting gear uptime while lessening parts stock reveal real advantages.

---Extended value chain: again and again, productivity stops at the edges of the organization. Streamlining cross-venture forms is the following extraordinary outskirts for decreasing costs, speeding tasks and conveyances to make an incentive for clients and investors.

5) Fabrication: Metal fabrication is the making of metal parts by cut them, bending them, and by assembling processes. It is an some value added process that includes the production of machines, parts, and structures from different crude materials. A manufacture shop will offer on an occupation, normally dependent on the designing illustrations, and whenever granted the agreement will construct the item. Substantial fab shops utilize a large number of significant worth included procedures in a single plant or office including welding, cutting, framing and machining. These substantial fab shops offer extra an incentive to their clients by restricting the requirement for obtaining faculty to find various merchants for various administrations. Metal creation employments as a rule begin with shop illustrations including exact estimations, at that point

move to the manufacture stage lastly to the establishment of the last undertaking. Manufacture shops are utilized by contractual workers, OEMs and VARs. Average activities incorporate free parts, auxiliary edges for structures and substantial gear, and stairs and hand railings for structures.

Fabrication contains or covers with different metalworking specialties:

---Fabrication shops and machine shops have covering abilities, however manufacture shops for the most part focus on metal readiness and get together as depicted previously. By correlation, machine shops likewise cut metal, yet they are more worried about the machining of parts on machine devices. Firms that include both fab work and machining are likewise normal.

---Blacksmithing has constantly included manufacture, despite the fact that it was not generally called by that name.

---The items created by welders, which are frequently alluded to as weldments, are a case of manufacture.

---Boilermakers initially had practical experience in boilers, prompting their exchange's name, however the term as utilized today has a more extensive importance.

---Thus, millwrights initially had some expertise in setting up grain factories and saw plants, however today they might be called upon for a wide scope of creation work.

---Ironworkers, otherwise called steel erectors, additionally take part in creation. Regularly the manufactures for auxiliary work start as pre-assembled sections in a fab shop, at that point are moved to the site by truck, rail, or freight ship, lastly are introduced by erectors.

6) Design: Techniques and methodologies contrast depending upon what you are growing however whether that includes forms in the medicinal sector area or item advancement at an organization we can state with a sureness that structure will assist you with finding new arrangements.

7) Resistance: Resistance– corrosion is a perplexing wonder which includes the connection between the mechanical procedures of strong molecule disintegration and the electrochemical procedures of consumption. An entire scope of issues is looked by an architect when endeavoring to acquire significant data on erosion consumption execution of a material. Among the requirements are the scattered test conditions and test rigs accessible in the writing making examinations and evaluating erosion consumption wear rates of various materials extremely troublesome. The point of this work is to assess the repeatability of erosion consumption tests and to examine the job of various parameters impacting erosion erosion.

8) Cost: Everything in this world depend upon the cost of the whatever material we going to use so basically have to give more importance on the cost and we should always take it in mind. Actually the cost of the material depends upon the design first because what we going make we made is should be perfect because if it is not then the whole money we going to invest is wasted. Also we should have to choose a good quality of the material because we cannot compromise here. So basically cost is a major factor is material selection.