Page 262 - Mechanical Engineer's Data Handbook

250 MECHANICAL ENGINEER'S DATA HANDBOOK
Silicone rubbers (SI) Shore hardness: 30-90. Temperature range:
- 116 "C to 315 "C (380 "C for intermittent use).
These have exceptionally high service temperature
ranges, but the mechanical properties and chemical Fluorosilicone rubbers
resistance are poor. They cannot be used for fuels, light
mineral oils, or high-pressure steam. They are used for These are similar to silicone rubbers but have better oil
high- and low-temperature seals, high-temperature resistance and a lower temperature range.
rotary seals, cable insulation, hydraulic seals, and Shore hardness: 40-80. Temperature range: - 64 "C
aircraft door and canopy seals. to 204 "C.

6.15 Wood

Permitted stresses in structural timbers (N mm-')
Timber Bending Compression

Stress in Horizontal Stress parallel Stress perpendicular
extreme fibre shear stress to grain to grain
Outside Dry All Outside Dry Outside Dry
location location locations locations location location location
Oak 8.3 9.7 0.9 6.0 6.9 1.6 3.5
Douglas fir 7.6 9 .O 0.6 6.0 6.9 1.6 2.1
Norway spruce 6.9 7.6 0.6 5.5 5.5 1.2 2.1

Meeh.nieel properties of timbers
Fibre Modulus Compressive
stress at of Modulus strength
elastic elasticity, of parallel Shear
Moisture Density, p limit E rupture to grain strength
wood (YO) (kgm-3) (Nmm-2) (Nmm-') (Nmm-') (Nmm-') (Nmm-')
Ash 15 657 60 10070 103 48 10
Beech - 740 -1 10 10 350 - 27-54 8.3-14
Birch 9-10 710 85-90 15 170 13&135 67-74 13-18.5
Elm, English - 560 40-54 11 790 - 17-32 8-1 I .3
Elm, Dutch - 560 4260 7 120 - 18-32 7.2-10
Elm, Wych - 690 65-100 7 860 - 2947 7.3-1 1.4
Fir, Douglas 6-9 530 4573 10340-15 170 71-97 49-74 748.8
Mahogany 15 545 60 8 690 80 45 6.0
Oak - 740 56-87 14 550 - 27-50 8-12
Pine, Scots - 530 41-83 85W10340 - 2142 5.2-9.7
Poplar - 450 4a-43 7 240 - 20 4.8
Spruce, Norway - 430 36-62 7380-8620 - 18-39 4.3-8
sycamore - 625 62-106 8970-13450 - 2646 8.8-15