Materials Selection in Engineering Applications M.G. More R & E (ACD) 1/17/2019 Kirloskar Pneumatic Co. Ltd.

Materials Selection Methodology & Factors of selection •Translate the design requirements into materials specifications. It should take into consideration the design objectives, constraints and free variables. •Screening out of materials that fail the design constraints. •Ranking the materials by their ability to meet the objectives. 1/17/2019 Kirloskar Pneumatic Co. Ltd.

Engineering Materials Plastics Metals Steel Stainless steel Die & tool steel Cast iron Ferrous Non-ferrous Aluminum Copper Zinc Titanium Tungsten Thermoplastics Acrylic Nylon ABS Polyethylene Polycarbonate PVC Thermosets Phenolic Polymide Epoxies Polyester Elastomers Rubber Polyurethane Silicone 1/17/2019 Kirloskar Pneumatic Co. Ltd.

Engineering Materials Ceramics Glass Carbides Nitrides Graphite Diamond Glasses Glass ceramics Composites Reinforced plastics Metal-Matrix Ceramic-Matrix Laminates Metals Plastics 1/17/2019 Kirloskar Pneumatic Co. Ltd.

Properties of Most Commonly Used Materials Ultimate Strength in tension 1/17/2019 Kirloskar Pneumatic Co. Ltd.

Cost of Most Commonly used Materials 1/17/2019 Kirloskar Pneumatic Co. Ltd.

Case Study-1 Heat Exchangers Constraints – 1. Support pressure difference ∆P 2. Resistance to fluid action (corrosion) 3. Operating temperature up to 150 to 200 °C 4. Modest cost Objective- Maximize heat flow per unit area (min. vol./wt. exchanger) Free variables- 1. Tube-wall thickness, (t) 2. Choice of material 1/17/2019 Kirloskar Pneumatic Co. Ltd.

q = h1∆T1 q = λ∆T/t background of heat flow, Heat transfer from one fluid, through a membrane to a second fluid, involves- convective transfer from fluid 1 into the tube wall, conduction through the tube wall, convection again to transfer it into fluid 2. The heat flux into the tube wall by convection is described by equation: (h1-heat transfer coefficient, ∆T1- temp drop across surface from fluid 1 into the wall) Conduction is described by the Fourier equation: (ג-thermal conductivity of wall THK (t), ∆T-temperature difference) q = h1∆T1 q = λ∆T/t 1/17/2019 Kirloskar Pneumatic Co. Ltd.

Then continuity of heat flux requires that the total resistance 1/U is, (1/h1 or 1/h2=thermal heat resistance at surface, t/ λ = thermal resistance at wall) Now, Total heat transfer from fluid 1 to fluid 2 is given by, q=U(T1-T2) (U=total heat transfer coefficient, T1-T2=temp. diff. bet 2 working fluids) In this case convective heat transfer is rapid and conduction through the wall dominates the thermal resistance (t/ λ) 1/17/2019 Kirloskar Pneumatic Co. Ltd.

M1= λσy-------------------(1) Our aim is to select a material to maximize the total heat transfer(Q), Where A is the area of tubes. Now, Now we know, The heat flow per unit area of tube wall, Q/A, is maximized by maximizing, M1= λσy-------------------(1) Further constraints- Fluid action, Cost , temp & MFG. After analysis, A preliminary search index M1 (material with good thermal conductivity & strength charc.) suggests copper alloys as one possibility. 1/17/2019 Kirloskar Pneumatic Co. Ltd.

Selection chart 1/17/2019 Kirloskar Pneumatic Co. Ltd.

Again exploring further, with following constraints, 150-200 °C on maximum service temperature, material cost of less than $4/kg Good resistance to corrosion. Now, Study/Survey stats- 1/17/2019 Kirloskar Pneumatic Co. Ltd.

-------------------(2) The study reveals that, copper-nickel alloys is handy, also problem of chemical reaction can be tackled. But, further constraints- Max. times its important to minimize the weight of heat exchangers. So repeating calc. to seek max value of Q/m (where m is the mass of the tubes) So instead of search index M1, -------------------(2) (ρ-density of tube material & strength σy is now raised to power 2 becoz the wt. depends on wall thickness as well as density, and wall thickness varies as 1/σy.) 1/17/2019 Kirloskar Pneumatic Co. Ltd.

-------------------(3) Finally looking for cheaper material, if the performance parameters are satisfied, -------------------(3) (where Cm is the cost per kg of the material) After analysing all parameters Aluminium Alloys are more preferable solution because they are light, cheap & equally strong as compared to other materials for H.E. Cost reduction in SAT-650 (material context)- SS piping instead of AL MFG difficulty & cost incurred in it. 1/17/2019 Kirloskar Pneumatic Co. Ltd.

Case Study-2 Materials for high-flow fans Commonly, the fan is driven by belt from drive-shaft of the engine/motor. The blades of fan are subjected both to centrifugal forces and bending moments caused by sudden acceleration of the motor/engine. 1/17/2019 Kirloskar Pneumatic Co. Ltd.

σ= F/A= ρω²R²---------------------- (σ=σf/factor of safety) The centrifugal force at the blade root is, F = ρ(RA)ω²R (where RA-volume of blade section & ω²R-Ang. Accl.) The force is carried by the section A, so the stress at the root of the blade is, σ= F/A= ρω²R²---------------------- (σ=σf/factor of safety) This stress must not exceed the failure stress σf, which does not affect the analysis and can be ignored. Thus for safety, ω < [(1/√R) x (σf/ρ)1/2] The length R is fixed, The safe angular velocity ω is maximized by selecting materials with large values of, M= σf/ρ 1/17/2019 Kirloskar Pneumatic Co. Ltd.

Selection chart 1/17/2019 Kirloskar Pneumatic Co. Ltd.

Selection must be balanced against the cost. Study/Survey stats- In chart σf vs ρ the Guidelines show that, materials above it have high values of M. Selection must be balanced against the cost. Study/Survey stats- Low cost fans can be made by die-casting a metal, or by injection-moulding a polymer. Polymers - Nylons and polypropylenes can be handy. Die-cast aluminium and magnesium alloys is one option. Composites are better, but more difficult to fabricate. Additional Info- If fan engine driven:-The problem is not really the fan, it is the undisciplined speed-changes of the engine which drives it. High speeds 1/17/2019 Kirloskar Pneumatic Co. Ltd.

More rugged fan design required. No flexibility, rigidity is dangerous which calls higher F.S. If fan motor driven:- Since fans are belt driven which limits its speeds (moderate) which are safe. More flexibility. Gives additional benefits in allowing independent control and more freedom in material selection. Final review:- 1/17/2019 Kirloskar Pneumatic Co. Ltd.

Material selection in Mechanical Engg. by Michael F. Ashby. References Material selection in Mechanical Engg. by Michael F. Ashby. Holman, J.P. (1981) Heat Transfer, 5th edition, McGraw-Hill, New York, USA. Barron RF. Cryogenics systems, 2nd ed. Oxford University Press; 1985. Paper published-Performance evaluation of counter flow heat exchangers by Prabhat Gupta , M.D. Atrey Cryogenics and Superconductivity Section, Centre for Advanced Technology (CAT), Indore 452 013, India Received 4 September 2000; accepted 13 November 2000 1/17/2019 Kirloskar Pneumatic Co. Ltd.

Thank you 1/17/2019 Kirloskar Pneumatic Co. Ltd.