Chapter 11 – Case studies Design and selection of materials for a turn buckle

Materials and Process Selection for Engineering Design: Mahmoud Farag

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A turnbuckle is a loop with opposite internal threads in each end for the threaded end of two ringbolts, forming a coupling that can be turned to tighten or loosen the tension in the members attached to the ringbolts.

Materials and Process Selection for Engineering Design: Mahmoud Farag

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Factors affecting performance in service The possible modes of service failure of the turnbuckle are:

1. Yielding of the loop or one of the ringbolts. 2. Shearing, or stripping, of threads on the loop or on one of the ringbolts. 3. Fatigue fracture of the loop or one of the ringbolts. 4. Creep strain in the loop or one of the ringbolts. 5. Fracture of the loop or one of the ring bolts as a result of excessive loading of the system or as a result of impact loading 6. Corrosion as a result of environmental attack and galvanic action between ringbolt and loop if they are made of different materials.

Materials and Process Selection for Engineering Design: Mahmoud Farag

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General specifications • The tensile force to applied by the turnbuckle consists of a static component, Lm = 20 kN and alternating component, La = 5 kN • Inner diameter of the rings at the end of ringbolts = 50 mm • Shortest distance between centers of rings on ringbolts = 300mm • Longest distance between centers of rings on ringbolts = 400mm • Other dimensions of the turnbuckle, which are material - independent, are shown in Fig. 11.1 • Service environment is industrial atmosphere.

Materials and Process Selection for Engineering Design: Mahmoud Farag

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Candidate materials I The design calculations in the book show that the strength of the loop material need not be as high as the ringbolt material. The two materials should not be far apart in the galvanic series to avoid galvanic corrosion. The ringbolt can be manufactured by several methods including: • From bar stock by threading and then forming the ring by bending. • From bar stock by upset forging to form a head, flattening the head and forming the ring by forging, and then threading as above. • Sand casting, shell molding, or die casting and then thread cutting. For the present case study, it is assumed that the available facilities favor the option of manufacturing the ringbolt from a bar stock by thread rolling and then bending round a die at room temperature. An elongation of at least15% will be needed for this. Materials and Process Selection for Engineering Design: Mahmoud Farag

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Candidate materials II The loop can be manufactured by several methods, including: • • • • • •

Sand casting using wooden or metal pattern and then thread cutting. Shell molding using metal pattern and then thread cutting.. Die casting and then thread cutting. Die forging of a bar stock and then thread cutting. Machining from a bar stock and then thread cutting. Welding of the threaded ends to round or square bars.

For the present case study, it is assumed that the available facilities favor sand casting for manufacturing the loop.

Materials and Process Selection for Engineering Design: Mahmoud Farag

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Table 11.2 Candidate materials for the ringbolt and loop materials Material

UTS (MPa)

YS (MPa)

Se’ (MPa)

ki

q

Kf

ρ

C

Relative cost* Mat. Mfr

Ringbolt materials (minimum elongation 15%) Steels AISI 1015 430 329 195 0.7 0.1 1.15 7.8 1 1 AISI 1040 599 380 270 0.6 0.2 1.30 7.8 1 1.1 AISI 1340 849 567 420 0.5 0.7 2.05 7.8 3 2.2 AISI 4820 767 492 385 0.55 0.6 1.90 7.8 3 2.5 Aluminum alloys AA 3003 O 112 42 56 0.7 0.1 1.15 2.73 4 5 AA 5052 O 196 91 90 0.65 0.4 1.60 2.68 4 7 AA6061 O 126 56 55 0.6 0.3 1.45 2.7 3 7 Copper-base alloys Al bronze 420 175 147 0.7 0.4 1.60 8.1 4 12 Si bronze 441 210 175 0.6 0.5 1.75 8.5 4 12 70/30 brass 357 133 145 0.75 0.3 1.45 8.5 4 10 ki is endurance limit modifying factor ρ is specific gravity C is corrosion resistance: 1 = poor, 2 = fair, 3 = good, 4 = very good. * Relative materials and processing costs are based on the cost of steel AISI 1015, which is taken as unity Materials and Process Selection for Engineering Design: Mahmoud Farag

1 4 4 8 1 1 1 6 6 4

7

Table 11.2 Candidate materials for the ringbolt and loop materials Material

UTS (MPa)

YS (MPa)

Se’ (MPa)

ki

q

Kf

ρ

C

Relative cost* Mat. Mfr

Loop materials (cast alloys) Gray cast irons ASTM A48-74 grade 20 140 140 70 0.5 0.2 1.30 7.5 4 grade 40 280 280 130 0.45 0.2 1.30 7.5 4 grade 60 420 420 168 0.4 0.2 1.30 7.5 4 Nodular cast irons ASTM A536 60040-18 420 280 210 0.6 0.2 1.30 7.5 4 80-55-06 560 385 280 0.55 0.2 1.30 7.5 4 120-90-02 840 630 420 0.5 0.2 1.30 7.5 4 Aluminum alloys AA 208.0 147 98 44 0.6 0.4 1.60 2.8 3 AA356.0 T6 231 168 79 0.5 0.5 1.75 2.68 4 AA B443.0 133 56 40 0.6 0.7 2.05 2.7 4 Copper-base alloys Al bronze 590 120 200 0.55 0.4 1.60 8.1 4 Si bronze 420 125 120 0.6 0.4 1.60 8.3 4 Mn bronze 640 340 300 0.5 0.5 1.75 8.3 4 ki is endurance limit modifying factor ρ is specific gravity C is corrosion resistance: 1 = poor, 2 = fair, 3 = good, 4 = very good. * Relative materials and processing costs are based on the cost of steel AISI 1015, taken as unity Materials and Process Selection for Engineering Design: Mahmoud Farag

1.2 1.25 1.3

1 1 1

1.9 2 2.1

4 4 4

5 5 4

1 1 1

12 12 11

6 6 6

which is 8

Selecting the optimum pair of materials The weighted properties method is used for this case study. The weighting factors are taken as 0.5, 0.3, and 0.2 for the cost, corrosion resistance, and weight respectively. The performance index (γ) of a turnbuckle made of a pair of materials is: γ = 0.5 (scaled relative cost) + 0.3 (scaled corrosion resistance) + 0.2 (scaled total weight) With this method of scaling, turnbuckles with lower numerical value of the performance index (γ) are preferable.

Table 11.3 shows that ferrous alloys are preferable. The main reasons for this are their lower cost and higher strengths. If the corrosion resistance is given a higher weight nonferrous alloys would be preferable. Materials and Process Selection for Engineering Design: Mahmoud Farag

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Table 11.3 Comparison of turnbuckle materials

Ringbolt AISI 1340 AISI 1340 AISI 1015 AISI 1340 AISI 1340 AISI 1015 AISI 1015 AISI 1340 AISI 1015 AISI 1015

Material pair Loop Nod. CI 120-90-02 Gray CI Grade 60 Gray CI Grade 60 Gray CI Grade 40 Nod. CI 80-55-06 Nod. CI 120-90-02 Gray CI Grade 40 Nod. CI 60-40-18 Nod. CI 80-55-06 Nod. CI 60-40-18

Relative total weight 1.082 1.221 1.220 1.313 1.117 1.091 1.314 1.152 1.126 1.161

Materials and Process Selection for Engineering Design: Mahmoud Farag

Relative cost 2.264 2.504 1.000 2.580 2.717 1.157 1.076 2.790 1.232 1.305

Merit value 1.748 1.896 1.944 1.952 1.982 1.997 2.001 2.025 2.041 2.085 10

Chapter 11 – Case studies Design and selection of materials for surgical implants

Materials and Process Selection for Engineering Design: Mahmoud Farag

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Hip joint prosthesis This case study discusses the design and selection of materials for a hip joint prosthesis. In this case, the femoral head is replaced by a rigid pin which is installed in the shaft of the femur while the pelvic socket (acetabulum) is replaced by a rigid or soft cup which is fixed to the ilium. Both the pin and cup can be fixed to the surrounding bone with an adhesive. Materials and Process Selection for Engineering Design: Mahmoud Farag

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Main dimensions and properties The compressive strength of compact bone is about 140 MPa, and the elastic modulus is about 14 GPa in the longitudinal direction and about 1/3 of that in the radial direction. These values are modest compared to most engineering materials. However, live healthy bone is self-healing and has a great resistance to fatigue loading. Materials and Process Selection for Engineering Design: Mahmoud Farag

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Loading conditions I The hip joint carries the repeated loading due to walking at a frequency about1 to 2.5 million cycles per year. The fatigue load is usually about 2.5-3 times the body weight. The joint is also subjected to a static loading as a result of muscle action which keeps the parts of the joint together. This is normally much smaller than the repeated loading. Assuming that the weight of the person is 75 kg and taking the alternating load as 3 times the weight, it can be shown that the hip prosthesis will be subjected to an alternating load of 2205 N. The maximum stress occurs in the prosthesis neck, which is about 30 mm diameter. From these values the alternating stress is estimated as 3.1 MPa. Assuming that the static load due to muscle contraction is about 300 N, the static stress at the neck of the prosthesis is about 0.42 MPa. Materials and Process Selection for Engineering Design: Mahmoud Farag

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Loading conditions II Using the modified Goodman relationship: (nm Kt Sm /UTS) + (na Kf Sa /Se) = 1 nm = factor of safety for static load, taken as 2 in this case. na = factor of safety for alternating loading, taken as 3. Kt = stress-concentration factor for static load, taken as 2.2. Kf = stress-concentration factor for alternating stress, taken as 3.5 Sm = static stress = 0.42 MPa, as calculated above. Sa = alternating stress = 3.1 MPa, as calculated above. UTS = ultimate tensile strength of the prosthesis material Se = endurance limit of the prosthesis material.

where

Take the endurance ration as 0.35, Se = 0.35 UTS The minimum strengths for implant materials are UTS = 95 MPa and Se = 33.25 MPa. Materials and Process Selection for Engineering Design: Mahmoud Farag

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Loading conditions III Wear considerations: Wear of the prosthesis parts (cup and pin) should also be considered when designing a hip joint prosthesis. Wear debris could cause adverse effects due to sensitivity of the patient to the material. Wear can cause enlargement of the cup resulting in poor articulation of the joint. The pressure between the mating surfaces can be estimated by dividing the force by the projected area of the cup. The force = 2205 + 300 = 2505 N The projected area of the cup is 1385 mm2. Average pressure = 1.8 MPa. The cup is usually made of a low - friction plastic, such as high density polyethylene and PTFE. Materials and Process Selection for Engineering Design: Mahmoud Farag

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Implant material requirements The pin and cup are fixed to the surrounding bone structure by an adhesive cement and perform different functions. In this case study the material for pin will be discussed. Similar procedure can be applied to the cup and cement.

Pin material requirements: • Tissue tolerance • Corrosion resistance • Mechanical behavior • Elastic compatibility • Weight • Cost Materials and Process Selection for Engineering Design: Mahmoud Farag

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The digital logic method is used to decide on the relative importance of the pin material requirements. Table 11.4 Main requirements and weighting factors for the pin of the hip joint prosthesis.

Property 1. Tissue tolerance (lower limit property) 2. Corrosion resistance (lower limit property) 3. Tensile strength (lower limit property) 4. Fatigue strength (lower limit property) 5. Toughness (lower limit property) 6. Wear resistance (lower limit property) 7. Elastic modulus (target value property) 8. Specific gravity (target value property) 9. Cost (upper limit property) Materials and Process Selection for Engineering Design: Mahmoud Farag

Weighting factor 0.2 0.2 0.08 0.12 0.08 0.08 0.08 0.08 0.08 18

Table 11.5 Properties of selected surgical implant materials Material

Tissue Corrosion Tensile Fatigue Elastic Relative Relative ρ tolerance resistance strength strength modulus Tough- wear (MPa) (MPa) (GPa) ness resistance

Stainless steels 316 10 317 9 321 9 347 9 Co-Cr alloys Cast alloy (1) 10 Wrought alloy (2) 10 Titanium alloys Unalloyed 8 Titanium Ti-6Al-4V 8 Composites (fabric reinforced) Epoxy-70% glass 7 Epoxy-63%carbon 7 Epoxy-62%aramid 7

C

7 7 7 7

517 630 610 650

350 415 410 430

200 200 200 200

8 10 10 10

8 8.5 8 8.4

8.0 8.0 7.9 8.0

9 9

655 896

425 600

238 242

2 10

10 10

8.3 3.7 9.1 4.0

10

550

315

110

7

8

4.5 1.7

10

985

490

124

7

8.3

4.4 1.9

7 7 7

680 560 430

200 170 130

22 56 29

3 3 3

7 7.5 7.5

2.1 3 1.6 10 1.4 5

Materials and Process Selection for Engineering Design: Mahmoud Farag

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1.0 1.1 1.1 1.2

Evaluation of candidate materials The limits on properties method is used to evaluate the candidate materials.  n Y  n X  n X m =   i     j     k k  1    i 1 X i  l  j 1 Yi  u  k 1 Yk t l

u

i

t

i

Using the notations of Eq. (9.8), the lower limits, Yi, upper limits, Yj, and target values, Yk, used in the calculations are: 1. Tissue tolerance, lower limit, Yi = 7. 2. Corrosion resistance, lower limit, Yi = 7. 3. Tensile strength, lower limit, Yi = 95 MPa. 4. Fatigue strength, lower limit, Yi = 33.25 MPa. 5. Toughness, lower limit, Yi = 2. 6. Wear resistance, lower limit, Yi = 7. 7. Elastic modulus, target value, Yk = 14 GPa. 8. Specific gravity, target value, Yk = 2.1. 9. Relative total cost, upper limit, Yj = 10. Materials and Process Selection for Engineering Design: Mahmoud Farag

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(9.8)

Ranking of pin materials Table 11.6 Merit parameter (m) and ranking of candidate materials for the pin of a hip joint prosthesis. Material

Merit parameter (m)

Rank

Ti-6 Al-4 V Co-Cr wrought alloy Unalloyed titanium 316 stainless steel 347 stainless steel 317 stainless steel 321 stainless steel Epoxy-70% glass fabric Co-Cr cast alloy Epoxy-62% Aramid fabric Epoxy-63% Carbon fabric

0.554 0.555 0.563 0.593 0.597 0.607 0.608 0.615 0.622 0.649 0.720

1 2 3 4 5 6 7 8 9 10 11

Materials and Process Selection for Engineering Design: Mahmoud Farag

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Chapter 11 – Case studies Design and selection of materials for lubricated journal bearing (The bearing is one of two that support the rotor of a centrifugal pump in its casting. The load on each bearing is 7500 N. The diameter of the rotor shaft is 80 mm and speed of rotation is 1,000 rpm)

Materials and Process Selection for Engineering Design: Mahmoud Farag

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Clearance (c) and shaft diameter (d) are usually in the range c/d = 0.001 – 0.0025 Length of bearing L is usually related to d, L/d = 0.8 – 2.0 Materials and Process Selection for Engineering Design: Mahmoud Farag

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Bearing material performance requirements I • The compressive strength of the bearing material at the operating temperature (120oC in the present case) must be sufficient to support the load acting on the bearing. • Fatigue strength is also important under conditions of fluctuating load. Both compressive and fatigue strengths increase as the thickness of the bearing material decreases. This is achieved by bonding a thin layer of the bearing material (0.05-0.15 mm) to a strong backing material to form a bimetal structure, e.g. lead and tin alloys on steel or bronze backs. An intermediate layer of copper or aluminum alloys may also be introduced to make a trimetal structure. In such cases, the bearing material can be made as thin as 0.013 mm (0.0005 in.). Materials and Process Selection for Engineering Design: Mahmoud Farag

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Bearing material performance requirements II • Conformability of the bearing material allows it to change its shape to compensate for slight deflections and misalignments. Lower Young's modulus is desirable. • Embeddability is the ability to embed grit or similar foreign particles to prevent them from scoring the journal. Lower hardness is desirable. • Wear resistance. • Thermal conductivity. • Corrosion resistance.

Materials and Process Selection for Engineering Design: Mahmoud Farag

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Minimum requirements for bearing material 1. Compressive strength is a lower-limit property. From the design calculations in the book, the minimum allowable roomtemperature compressive strength 20 MPa. 2. Fatigue strength the minimum allowable 20 MPa. 3. Hardness is an upper-limit property with a maximum 100 BHN. 4. Young's modulus, upper-limit property with a maximum 100 GPa, 5. Wear resistance is a lower-limit property, usually given as excellent (5), very good (4), good (3), fair (2) and poor (1). 6. Corrosion resistance is a lower-limit property, given as excellent (5), very good (4), good (3), fair (2) and poor (1) 7. Thermal conductivity is a lower limit property, minimum conductivity of 20 W/m K 8. Cost of the bearing material, backing material and fabrication. Materials and Process Selection for Engineering Design: Mahmoud Farag

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Classification of bearing materials Many alloy systems have been specially developed to accommodate the conflicting requirements that have to be satisfied by bearing materials. They can be classified into: • Whitemetals (babbitt alloys). These are either tin-base or lead-base • Copper-base bearing alloys of a wide range of strengths and hardness. • Aluminum-base bearing alloys for high-duty because of their good thermal conductivity. • Nonmetallic bearing alloys are mostly based on polymers or polymer-matrix composites. They are widely used under conditions of light loading because their low thermal conductivities. Materials and Process Selection for Engineering Design: Mahmoud Farag

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Table 11.7 Composition of some bearing alloys (%) Alloy Sn Sb Pb Cu grade White metals ASTM B 23 (tin base) 1 91 4.5 0.35 4.5 2 89 7.5 0.35 3.5 3 84 8 0.35 8 4 75 12 10 3 5 65 15 18 2 White metals ASTM 23 (lead base) 6 20 15 63.5 1.5 7 10 15 75 0.5 8 5 15 80 0.5 10 2 15 83 0.5 11 15 Rem. 0.5 15 1 15 Rem. 0.5 Copper base alloys SAE (copper-lead) 48 0.25 28 Rem. 49 0.5 24 Rem. 480 0.5 35 Rem. Copper base alloys ASTM B22 (bronze) A 19 0.25 Rem. B 16 0.25 Rem. C 10 10 Rem. Aluminum base alloys 770 6 1 780 6 1 MB7 7 1

Fe

Zn

Al

Other

0.08 0.08 0.08 0.08 0.08

0.005 0.005 0.005 0.005 0.005

0.005 0.005 0.005 0.005 0.005

0.08 0.08 0.08 0.15 0.15

0.08 0.1 -

-

-

0.15 As 0.6 As 0.2 As 0.2 As 0.25 As 1.4 As

0.35 0.35 0.35

0.1 -

-

1.5 Ag, 0.025 P

0.25 0.25 0.15

0.25 0.25 0.75

-

1P 1p 0.1 P. 1 Ni

0.7 0.7 0.6

-

Rem. Rem. Rem.

1 Ni, 0.7 Si 0.5 Ni, 1.5 Si 1.7 Ni, 0.6 Si 28

Materials and Process Selection for Engineering Design: Mahmoud Farag

Bi, 0.1 As Bi, 0.1 As Bi, 0.1 As As As

15 Ag

Table 11.8 Properties of some bearing materials Allo y grad e

Yield strengt h (MPa)

Fatigu Hardne Corrosio e ss n strengt (BHN) resistanc h e (MPa) White metals ASTM B 23 (tin base) 1 30 27 17 5 2 42.7 34 25 5 3 462 37 37 5 4 38.9 31 25 5 5 35.4 28 23 5 White metals ASTM 23 (lead base) 6 26.6 22 21 4 7 24.9 28 23 4 8 23.8 27 20 4 10 23.8 27 18 4 11 21.4 22 15 4 15 28.0 30 21 4 Copper base alloys SAE (copper-lead) 48 40 45 28 3 49 45 50 35 3 480 38 42 26 3 Copper base alloys ASTM B22 (bronze) A 168 120 100 2 B 126 100 100 2 C 119 91 65 2 Aluminum base alloys 770 173 150 70 3 780 158 135 68 3 MB 193 170 73 3 7

Wear resistan ce

Thermal conducti on (W/m K)

Young ’s modul us (GPa)

Relativ e cost

2 2 2 2 2

50.2 50.2 50.2 50.2 50.2

51 53 53 53 53

7.3 7.3 7.3 7.3 7.5

3 3 3 3 3 3

23.8 23.8 23.9 23.9 23.9 23.9

29.4 29.4 29.4 29.4 29.4 29.4

1.3 1.2 1.1 1 1 1

5 5 5

41.8 41.8 41.8

75 75 75

1.5 1.5 1.5

5 5 3

41.8 41.8 42

95 95 77

1.8 1.8 1.6

2 2 2

167 167 167

73 73 74

1.5 1.5 1.5

Materials and Process Selection for Engineering Design: Mahmoud Farag

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The digital logic method is used to decide on the relative importance of the bearing material requirements.

Table 11.9 Weighting factors of the selection criteria for the bearing material of centrifugal pump. Property Yield strength Fatigue strength Hardness Corrosion resistance Wear resistance Thermal conductivity Young's modulus Cost Total

Weighting factor 0.20 0.14 0.08 0.11 0.11 0.20 0.08 0.08 1.00

Materials and Process Selection for Engineering Design: Mahmoud Farag

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Selecting the optimum bearing material The limits on properties method was used according to the values: • Lower limit of yield strength = 20 MPa • Lower limit of fatigue strength = 20 MPa • Lower limit on thermal conductivity = 20 W/(m.K) • Lower limit on corrosion resistance =2 • Lower limit on wear resistance =2 • Upper limit on hardness = 100 BHN • Upper limit on Young's modulus = 100 GPa • Upper limit on relative cost = 7.5 The above lower and upper limits were used to calculate the merit parameters (m) of the different materials using Eq. (9.8). The results of evaluation are given in Table 11.10. Materials and Process Selection for Engineering Design: Mahmoud Farag

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Table 11.10 Merit parameter and suitability of bearing materials Material Merit parameter (m) White metals ASTM b23 (tin base) 1 0.59 2 0.54 3 0.54 4 0.56 5 0.56 White metals ASTM 23 (lead base) 6 0.63 7 0.61 8 0.62 10 0.61 11 0.66 15 0.58 Copper base alloys SAE (copper-lead) 48 0.47 49 0.47 480 0.49 Copper base alloys ASTM B22 (bronze) B 0.49 C 0.49 Aluminum base alloys 770 0.37 780 0.38 MB7 0.37 Materials and Process Selection for Engineering Design: Mahmoud Farag

Suitability 8 5 5 6 7 11 9 10 9 12 6 3 3 4 4 4 1 2 1 32

Chapter 11 – Case studies Analysis of the requirements and substitution of materials for tennis rackets (sports industries use sophisticated materials and high-tech to manufacture their products. Biomechanics is also being used to enhance player comfort and to optimize equipment performance. As a result, the shape and the materials used in making many sports equipment have undergone considerable change). Materials and Process Selection for Engineering Design: Mahmoud Farag

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All these rackets comply with the ITF limit on length (32 in) and head (15.5 in length and 11.5 in width). Although there are no limitations on the racket weight, it usually ranges between 13 and 15 ounces.

Materials and Process Selection for Engineering Design: Mahmoud Farag

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Functional requirements of the tennis racket • Tennis racket can be considered as an implement for transmitting power from the arm of the player to the ball. This should be done as efficiently as possible in order to allow the player to deliver the fastest balls with the least effort (power). • Playability is a subjective evaluation of the overall performance of the racket and may be considered as a function of control and vibrations. • Control is the ability to give the ball the desired speed and spin and to place it in the desired area of the court. Vibrations take place in the strings as a result of hitting the ball, and are then transmitted to the player's arm through the racket frame, which if not dampened would cause the player to tennis elbow. • The performance is also influenced by strings material and tension. • The present case study will only consider Materials and Process Selection for Engineering Design: Mahmoud Farag

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Frame materials and performance indices • Tennis rackets can be made of several materials (various types of wood, Al alloys, steels, and fiber-reinforced composites). • With their much better performance at reasonable price, CFRP currently represent the favorable material for tennis rackets. • To improve the performance of their rackets, manufacturers are examining plastics reinforced with carbon nanotubes (CNTRP) as possible substitutes for CFRP. CNTRP provide better properties but are more expensive. • This case study uses the cost-benefit analysis to evaluate CNTRP as possible substitute for CFRP in tennis rackets. The cost is that of the material per unit mass while the benefit is considered to consist of two elements, power and damping. Materials with higher E/ρ give higher power and those with lower E give better damping. Materials and Process Selection for Engineering Design: Mahmoud Farag

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Table (11.11) Properties of candidates for making a tennis racket (Based on paper by Esawi and Farag) Ec (GPa) Epoxy+5%CNT 130.4 Epoxy+20%CNT 425.6 Epoxy+30%CNT 622.4 Epoxy+50%CF 136 Epoxy+55%CF 146.4 Epoxy+60%CF 156.8 Epoxy+65%CF 167.2 Epoxy+1%CNT+64%CF 184.8 Epoxy+3%CNT+62%CF 220 Epoxy+5%CNT+60%CF 255.2 Epoxy+10%CNT+55%CF 343.2 Epoxy+15%CNT+50%CF 431.2

Density ρc (g/cc) 1.843 1.852 1.858 1.87 1.873 1.876 1.879 1.879 1.879 1.879 1.879 1.879

Specific Modulus (E/ρc) (GPa)/(g/cc) 70.75421 229.8056 334.9839 72.72727 78.16337 83.58209 88.9835 98.35019 117.0836 135.8169 182.6503 229.4838

Materials and Process Selection for Engineering Design: Mahmoud Farag

Cost Cc* ($/kg) 2152.357 8579.429 12864.14 92.5 100.75 109 117.25 544.0714 1397.714 2251.357 4385.464 6519.571 37

Ranking of alternative substitutes I The AHP is used to assess the cost-benefit analysis of the materials in Table 11.11. The AHP decision tree is shown in Figure 11.7. The cost is taken as the price of the material in $/kg. The benefits consist of improved power (increases with E/ρ) and improved damping (high, medium and low for E less than 200 GPa, 200 to 300 GPa, and above 300 GPa respectively). Various scenarios for material substitution are developed by allocating different weights to the cost, power and damping. The resulting rankings are shown in Table 11.12.

Materials and Process Selection for Engineering Design: Mahmoud Farag

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Fig. 11.7 Decision tree for AHP analysis – tennis racket frame materials

Materials and Process Selection for Engineering Design: Mahmoud Farag

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Table 11.12 Ranking of Materials According to AHP (Based on paper by Esawi and Farag) Altern ative

1

Weights Cost/ Power/ Benefit damping 50%/50% 50%/50%

2

30%/70%

Highest

Second

 Epoxy +65%CF

 Epoxy +60%CF

8

15%/85%

70%/30%

 Epoxy+1%CNT+ 64%CF  Epoxy+1%CNT+ 64%CF  Epoxy+1%CNT+ 64%CF  Epoxy+1%CNT+ 64%CF  Epoxy+1%CNT+ 64%CF  Epoxy+1%CNT+ 64%CF  Epoxy+30%CNT

9

10%/90%

70%/30%

 Epoxy+30%CNT

3 4

70%/30% 25%/75%

5 6

60%/40%

60%/40% 70%/30%

20%/80%

7

60%/40% 70%/30%

Top ranking materials Third

Fourth  Epoxy+50%CF

 Epoxy+ 65%CF

 Epoxy+1%CNT+ 64%CF  Epoxy +55%CF  Epoxy+60%CF

 Epoxy+ 65%CF

 Epoxy+60%CF

 Epoxy+55%CF

 Epoxy+65%CF

 Epoxy+60%CF

 Epoxy+55%CF

 Epoxy+65%CF

 Epoxy +60%CF

 Epoxy+55%CF

 Epoxy+65%CF

 Epoxy +60%CF

 Epoxy+55%CF

 Epoxy +65%CF

 Epoxy +60%CF

 Epoxy+1%CNT+ 64%CF  Epoxy+1%CNT+ 64%CF

 Epoxy +65%CF

 Epoxy+55%CF  Epoxy+30%CNT  Epoxy +60%CF

 Epoxy +65%CF

 Epoxy +60%CF

Materials and Process Selection for Engineering Design: Mahmoud Farag

 Epoxy+55%CF

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Ranking of alternative substitutes II Conclusion:

The material ranking is sensitive to the weight allocated to cost, power, and damping. Higher weight for the cost favors the traditional Epoxy-CF composites. Epoxy-CF-CNT hybrid composites become more viable as the weight allocated to cost is reduced and the emphasis on power is increased. The epoxy-CNT composites become viable alternatives only at the two lowest weights for cost, and the consequent highest emphasis on benefits, with higher emphasis on power. Materials and Process Selection for Engineering Design: Mahmoud Farag

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Chapter 11 – Case studies Material substitution in automotive industry The major driving forces behind material substitution in the automotive industry are cost reduction, better fuel economy, improved aesthetics and comfort, and compliance to new legislation. Such substitution must be made cost-effectively while conforming to the increasingly severe safety and quality standards, and without unduly restricting the freedom of the stylist. Materials and Process Selection for Engineering Design: Mahmoud Farag

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Materials Substitution for automotive interior panels: performance indices The material performance index (m) for a stiff light panel is: m = E1/3/ρ (11.19) Where E is elastic modulus and ρ is density. The thickness of another panel of equal stiffness and resistance to buckling is givens as: tn = to (Eo/En)1/3 (11.20) where tn and to = thicknesses of new and currently used panels En and Eo = elastic constants of new and current materials The mass (M) of the panel is: M = ρ t b l (11.21) where l, b and t are length, width, and thickness of the panel. Thermal distortion index M2 is a function of thermal conductivity divided by thermal expansion coefficient. Higher M2 is preferred. Materials and Process Selection for Engineering Design: Mahmoud Farag

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Materials Substitution for automotive interior panels: Cost, aesthetic and environmental considerations The total cost of a panel is considered to consist of 4 elements: Ct = C1 + C2 + C3 + C4 (11.5) Where C1 is cost of material, C2 is cost of manufacturing and finishing, C3 is cost over the entire life of the component, C4 is cost of disposal and recycling. For simplicity, C4 will not be considered The cost items for candidate materials are in Table 11.13. Wood has optimum aesthetic value (100 units), other materials are ranked according to their distance from it on a tactile warmthtactile softness chart by Ashby and Johnson, see Table 11.14. According to the discussion in the book, the environmental impact of a given panel will be taken as proportional to its weight. Materials and Process Selection for Engineering Design: Mahmoud Farag

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Table (11.13) Technical, cost and environmental considerations (values based on Ashby and Johnson, Ermolaeva et al, and Matos and Simplicio) Material

PVC PP + glass fibers (40%) Epoxy + carbon fibers (60%) Cork Wood (Ash/Willow) PP + flax fibers (40%) PP + hemp fibers (40%) PP + jute fibers (40%)

E Density Weight (GPa) (g/cc) of Panel (kg) 2 1.30 2.4 7.75 1.67 3.3

Material Cost (USD) 3.3 6.0

Manufacturing Cost (USD)

M2 (W m-1)

2.0 2.0

Running Cost (USD) 12.2 21.8

69

1.6

1.46

27.2

5.0

9.6

700,000

0.02 10

0.2 0.85

1.74 0.927

14.0 1.18

17.0 17.0

11.5 6.12

400 60,000

4.65

1.19

1.67

1.9

2.0

11.0

50,000

6.0

1.236

1.6

1.8

2.0

10.6

50,000

3.96

1.174

1.76

1.9

2.0

11.6

50,000

Materials and Process Selection for Engineering Design: Mahmoud Farag

250,000 60,000

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Table (11.14) Aesthetic and comfort characteristics of candidate materials (values based on Ashby and Johnson, Ermolaeva et al, and Matos and Simplicio) Indices

PVC PP + glass fibers(40%) Epoxy + carbon fibers (60%) Cork Wood (Ash/Willow) PP + flax fibers (40%) PP + hemp fibers (40%) PP + jute fibers (40%)

Aesthetics M1 (W s1/2/m2 K) (Normalized) 80 780 (19.2) 75 1460 (10.3) 70 1460 (10.3) 85 150 (100) 100 730 (20.5) 80 1460 (10.3) 80 1460 (10.3) 80 1460 (10.3)

Materials and Process Selection for Engineering Design: Mahmoud Farag

Sound damping/ Loss Coefficient (Normalised) 0.08 (40) 0.03 (15) 0.03 (15) 0.20 (100) 0.05 (25) 0.08 (40) 0.08 (40) 0.08 (40) 46

Table (11.15) Weight and cost of panels and M2 of materials Material Weight of Total Cost of M2 (W m-1) Panel (kg) Panel (USD) (Normalized) (Normalized) (Normalized) PVC 2.4 (38.6) 17.5 (82.3) 250,000(35.7) PP+ glass fibers (40%) 3.3 (28.2) 29.8 (48.3) 60,000 (8.6) Epoxy + carbon fibers (60%) 1.46 (63.5) 41.8 (34.4) 700,000 (100) Cork 1.74 (53.3) 42.5 (33.9) 400 (0.057) Wood (Ash/Willow) 0.927 (100) 24.3 (59.3) 60,000 (8.6) PP + flax fibers (40%) 1.67 (55.5) 14.9 (96.6)) 50,000 (7.1) PP + hemp fibers (40%) 1.6 (57.9) 14.4 (100) 50,000 (7.1) PP + jute fibers (40%) 1.76 (52.7) 15.5 (92.9) 50,000 (7.1) Materials and Process Selection for Engineering Design: Mahmoud Farag

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Comparison of candidate materials-Performance/cost method The performance of a material is the weighted sum of the normalized values of its aesthetics, M1, and M2, as shown in Table 11.16. Compared with PVC, PP + glass fibers (40%) gives lower performance at a higher cost and is, therefore, rejected. PP + flax fibers (40%), PP + hemp fibers (40%), and PP + jute fibers (40%) give similar performance to PVC but at a lower cost. They are preferable if cost reduction is the objective. PP + hemp fibers (40%) is the top ranking as it has the highest performance/cost. Epoxy + carbon fibers(60%), cork, and wood give higher performance at a higher cost than PVC. They are preferable if raising performance is the objective. Wood has the highest performance/cost. Materials and Process Selection for Engineering Design: Mahmoud Farag

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Table (16) Results of the Performance/Cost Method of substitution Index Aesthetics M1 Sound Weight M2 Performance Cost Perform/cost Evaluation and damping of (USD) rank panel Weighting factor 0.2 0.2 0.1 0.4 0.1 PVC PP + glass fibers (40%)

16 15

3.8 4 2.1 1.5

15.5 11.3

3.6 42.9 0.9 30.8

17.5 29.8

2.5 1.03

Epoxy + carbon fibers (60%) 14

2.1 1.5

25.4

10 53

41.8

1.3

Cork

17

20 10

21.3

0.01 68.3

42.5

1.6

Wood (Ash/Willow)

20

4.1 2.5

40

0.9 67.5

24.3

2.8

PP + flax fibers (40%) PP + hemp fibers (40%) PP + jute fibers (40%)

16 16 16

2.1 4 2.1 4 2.1 4

22.2 23.2 21.1

0.7 45 0.7 46 0.7 43.9

14.9 14.4 15.5

3 3.2 2.8

Materials and Process Selection for Engineering Design: Mahmoud Farag

Current material Lower performance and higher cost-reject Better performance rank 3 Better performance rank 2 Better performance rank 1 Lower cost rank 2 Lower cost rank 1 Lower cost rank 3 49

Comparison of candidate materials-compound objective function method Two substitution scenarios were created by changing the weighting factors as follows: • More emphasis on cost than aesthetics and comfort, economy model. 75% technical and economic, 25% aesthetic and comfort. • Less emphasis on cost than aesthetics and comfort, luxury model. 50% technical and economic, 50% aesthetic and comfort. The results are given in Table 11.17. • For the economy model, PP + hemp fibers (40%) and PP + flax fibers (40%) receive first and second ranks respectively, • For the luxury model, cork and wood have close COF values and, therefore, share the top rank. Materials and Process Selection for Engineering Design: Mahmoud Farag

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Table (17) Results of the Compound Objective Function Method of substitution Material

PVC PP + glass fibers (40%) Epoxy + carbon fibers (60%) Cork Wood (Ash/Willow) PP + flax fibers (40%) PP + hemp fibers (40%) PP + jute fibers (40%)

Scenario I (Economy Model) COF Rank 58.5 5 36.6 8 48.6 7 50.3 63.0 64.8 66.8 62.7

6 3 2 1 4

Materials and Process Selection for Engineering Design: Mahmoud Farag

Scenario II (Luxury Model) COF Rank 54.7 6 38.1 8 50.5 7 63.8 63.4 56.7 57.9 55.4

1 1 4 3 5 51

Conclusion • Two methods are used to examine the case of material substitution for interior motorcar panels and they yielded consistent results. • PP + hemp fibers (40%) and PP + flax fibers (40%) rank highest for the economy models, where cost is important • Wood and cork rank highest for the luxury models, where aesthetics and comfort are important. • These results are consistent with the current trends in industry. Based on these results, it is expected that natural fiber reinforced plastics would be increasingly used as automotive materials.

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