TOUGHNESS PHYSICAL PROPERTIES OF WOOD Toughness is the reverse of stiffness, or the ability to bend without breaking. Toughness is one of the most useful properties of wood, and is especially desirable in handles, spokes, and various other articles.
The toughness of wood is not exactly determined by any single mechanical test. Perhaps it is best indicated by two tests which the engineers* designate as the "work to maximum load," and "resistance to impact." The work to maximum load is expressed in inch-pounds per cubic inch; and the resistance to impact, in the height in inches necessary to drop a 50-pound hammer to cause complete breakage of the stick tested. The results of tests of this character are given in Table 7.
As a class, the hardwoods are nearly three times as tough as the softwoods, although, as in previous tests, there is an overlapping of the two groups. Alpine fir is the least tough of the softwoods, and longleaf pine the toughest, the latter being tougher than a number of hardwoods. Basswood and buckeye have the least toughness among the hardwoods; and hickory and osage orange are the toughest, the range being very wide.
Table 7 Toughness Tests of Various Woods Woan TO MAXIMUM LOAD (Inch-pounds per Cubic Inch) Softwoods Fir, Alpine 4.4 Pine, Norway 6.8 Cedar, Western Red ... 4.5 Pine, White 5.9 Spruce, Englemann.... 4.9 Spruce, Red 6.1 Pine, Sugar 6.0 Fir, Grand 6.2 Cypress 6.1 Spruce, White 6.6 Pine, Table Mountain.. 6.1 Douglas Fir 6.6 Pine, Western Yellow.. 5.1 Hemlock, Eastern 6.7 Pine, Lodgepole 6.2 Tamarack 7.2 Fir, White 6.2 Pine, Longleaf 8.1 Cedar, Northern White. 6.7 Average Work to Maximum Load 5.7 Hardwoods Basswood 5.3 Willow 12.9 Buckeye 5.4 Ash, Green 13.0 Aspen, Largetooth 6.1 Elm, Slippery 13.9 Cherry, Red 6.2 Oak, Swamp White .... 14.6 Sycamore 7.1 Ash, Blue 14.7 Tupelo 7.8 Locust, Black 15.4 Butternut 8.1 Birch, Sweet 15.6 Oak, Post 9.1 Ash, White 15.6 Ash, Pumpkin 9.4 Hackberry 16.6 Cucumber 10.0 Birch, Yellow 16.6 Maple, Red 10.6 Locust, Honey 17.3 Oak, Bur 10.7 Hickory, Water 18.8 Sumac 10.8 Elm, Rock 19.4 Maple, Silver 11.0 Witch Hazel 19.5 Elm, White 11.3 Hickory, Bitternut 20.0 Oak, Red 11.3 Hickory, Shagbark 20.2 Oak, White 11.4 Dogwood 21.0 Maple, Sugar 12.0 Hickory, Nutmeg 22.8 Ash, Black 12.2 Hickory, Mockernut.... 24.8 Oak, Yellow 12.4 Hickory, Pignut 29.5 Laurel, Mountain 12.5 Hickory, Big Shellbark . 30.2 Beech 12.5 Osage Orange 37.9 Cherry, Black 12.8 Average Work to Maximum Load 14.6 Table 7—(Concluded) RESISTANCE TO IMPACT (Height in inches at which drop of a 50-lb. hammer caused breakage of test piece) Softwoods Fir, Alpine 9 Pine, Western Yellow .... 19 Pine, Table Mountain.. 10 Hemlock, Eastern 20 Spruce, Englemann 14 Douglas Fir 20 Cedar, Northern White... 15 Cypress 23 Cedar, Western Red 16 Fir, Grand 25 Pine, Lodgepole 16 Tamarack 28 Pine, Sugar 17 Pine, Norway 28 Fir, White 18 Pine, Longleaf 36 Pine, White 18 Average Resistance to Impact 19 Hardwoods Basswood 16 Oak, White 40 Buckeye, Yellow 18 Witch Hazel 40 Aspen 18 Oak, Red 40 Cherry, Red 22 Ash, Blue 43 Butternut 23 Birch, Sweet 44 Sycamore 24 Elm, Slippery 44 Tupelo 25 Locust, Black 44 Maple, Red 29 Oak, Bur 44 Maple, Silver 29 Willow 44 Cucumber 30 Elm, Rock 48 Ash, Pumpkin 31 Oak, Swamp White 50 Ash, Black 32 Hackberry 53 Laurel, Mountain 32 Hickory, Nutmeg 64 Cherry, Black 33 Hickory, Water 56 Elm, White 34 Locust, Honey 56 Maple, Sugar 36 Dogwood 58 Ash, Green 37 Hickory, Bitternut 66 Ash, White 37 Hickory, Shagbark 71 Oak, Post 38 Hickory, Mockernut 82 Oak, Yellow 39 Hickory, Pignut 91 Beech 40 Hickory, Big Shellbark ...105 Birch, Yellow 40 Osage Orange 120 Average Resistance to Impact 45