Bathtub

• A bathtub is a large container for holding

water in which a person may bathe.

Selecting the Right Bath Tub

• RULE 1. First determine the exact

dimensions of the space where the tub will

be placed and then consider the types of

installations that could fit into that area.

• RULE 2. Investigate the advantages and

disadvantages of commonly used bathtub

materials to determine which will work best

for you.

• RULE 3. Find a bath that is a comfortable

fit for the person who will use it the most.

RULE 4. Consider quality first and price

second.

Requirement

1. corrosion resistance

2. tough material

3. temp. adaptation

4. Wear Resistance

5. high strength

Raw Materials

• Cast Iron

The metal base for bathtubs is made of gray

cast iron (containing carbon, silicon,

manganese, phosphorus, and sulfur),

titanium steel, zero carbon steel, or partially

decarburized steel. These compositions

have been specially designed for enameling.

• Porcelain on steel

The tub is stamped from a thin sheet of

steel, then finished with a layer of porcelain

enamel. These tubs are durable and easy to

clean. The finish is resistant to most

common chemicals, and retains its gloss for

a long time

• Composites

Toughness, low cost, light weight, ease of

installation, and a finish that can be repaired

• Polymer Matrix Composite

FRP composites can be designed with very

high strength-to-weight and modulus-to-

weight ratios

Material Selection

• Selection:

Matrix: Epoxy

Reinforcement: Glass Fiber

Matrix properties

Tensile strength 85 N/mm²

Tensile Modulus 10,500 N/mm²

Elongation at break 0.8%

Flexural strength 112 N/mm²

Flexural Modulus 10,000 N/mm²

Compressive Strength 190 N/mm²

Coefficient of linear thermal expansion 34 10-6

Fiber Properties

Material: E-Glass Fibre

Composition: 54%SiO2-15%Al2O3-12%CaO

Property Minimum

Value (S.I.)

Maximum Value

(S.I.)

Units (S.I.)

Density 2.55 2.6 Mg/m3

Fracture Toughness 0.5 1 MPa.m1/2

Hardness 3000 6000 MPa

Poisson's Ratio 0.21 0.23

Tensile Strength 1950 2050 MPa

Young's Modulus 72 85 GPa

Maximum Service Temperature 620 630 K

Minimum Service Temperature 0 0 K

Resistivity 1e+022 1e+023 10-8 ohm.m

• fracture toughness values (K 1c)

𝑘1𝐶 = 122.43 MPa.𝑚−1

2

Each layer has different orientation

• Generally large in size but low in

production quantity - not economical for

high production

• Two processes called hand lay-up and

spray lay-up are used to make fiberglass

bathtubs.

Hand lay-up is a method in which

successive plies of reinforcing material or

resin-impregnated reinforcement are

positioned in a mold by hand. Cure occurs at

room temperature with no applied pressure

The spray lay-up process is faster than hand

lay-up and involves feeding a stream of

chopped fibers into a spray of liquid plastic

in a mold cavity.

• The direction of the fibers is random and

the process is usually automated. After

lay-up is completed, the plastic must

solidify or cure in a reasonable time at

room temperature, which occurs via

chemical reactions.

𝑙𝑐 =𝜎𝑓∗𝑑

2 𝜏𝑐

• 𝜏𝑐 =150

2= 75 𝑀𝑃𝑎

• 𝜎𝑓∗ = 2000 𝑀𝑃𝑎

• 𝑑 = 20 𝜇𝑚

𝑙𝑐 =2000 × 20

2 × 75= 266.6 𝜇𝑚

• 𝑙 = 50𝑚𝑚 > 15 𝑙𝑐

class 20 gray iron

Tensile Strength Ultimate152 MPa, or 22.0

103 psi

Hardness Brinell 156

Tensile Strength Yield (Proof) 98 MPa, or 14

103 psi

Specific gravity 7.03 - 7.13

𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑠𝑡𝑟𝑒𝑛𝑔𝑡ℎ =152

7.03= 21.33 𝑀𝑃𝑎

𝜎𝑐𝑙∗ = 𝜎′𝑚 1 − 𝑣𝑓 + 𝜎𝑓

∗𝑣𝑓

• 450 = 150 1 − 𝑣𝑓 + 2000 × 𝑣𝑓

• 𝑣𝑓 = 0.162 = 16%

𝛿𝑐 = 𝛿𝑓𝑣𝑓 + 𝛿𝑚𝑣𝑚𝛿𝑢 = 2.58 × 0.16 + 1.25 × 1 − 0.16 = 1.46

𝑐𝑜𝑚𝑝𝑜𝑠𝑖𝑡𝑒 𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑠𝑡𝑟𝑒𝑛𝑔𝑡ℎ =450

1.46= 308.22 𝑀𝑃𝑎

• Thanks