Load Duration and Seasoning Effects on Mortise & Tennon Joinery

Table 3-3 Comparison of Combined Test Results with Weaker/Softer Material
Test
Mathematically Combined
Physically Combined
Difference (Mathematically/Physically)
Number Yield Stress (lbs/in 2 ) Stiffness (lbs/in 3 ) Yield Stress (lbs/in 2 ) Stiffness (lbs/in 3 ) Yield Stress Stiffness
M01 1,760 15,900 1,840 18,200 0.96 0.87
M02 1,870 16,000 1,840 18,200 1.02 0.88
M03 1,420 10,700 1,530 14,700 0.93 0.73
M04 1,350 10,400 1,530 14,700 0.88 0.71
M05 1,480 11,900 1,510 13,700 0.98 0.87
M06 1,390 9,700 1,510 13,700 0.92 0.71
M07 1,460 13,700 1,880 19,700 0.78 0.70
M08 1,690 16,000 1,880 19,700 0.90 0.81
M09 1,460 12,300 1,560 13,800 0.94 0.89
M10 1,440 10,900 1,560 13,800 0.92 0.79
M11 1,580 13,200 1,700 17,600 0.93 0.75
M12 1,540 12,900 1,700 17,600 0.91 0.73
M13 1,960 29,500 2,470 27,900 0.79 1.06
M14 2,160 26,100 2,470 27,900 0.87 0.94
M15 1,540 13,200 1,570 13,800 0.98 0.96
M16 1,510 11,600 1,570 13,800 0.96 0.84
Mean 0.92 0.83
St<strong>and</strong>ard Deviation 0.06 0.10
Test
Mathematically Combined Physically Combined Difference (Mathematically/Physically)
Number Yield Stress (lbs/in 2 ) Stiffness (lbs/in 3 ) Yield Stress (lbs/in 2 ) Stiffness (lbs/in 3 ) Yield Stress Stiffness
T01 4,890 115,300 3,460 90,400 1.41 1.28
T02 4,590 118,200 2,620 84,400 1.75 1.40
T03 4,960 120,300 2,270 80,600 2.19 1.49
T04 4,660 98,300 3,170 100,100 1.47 0.98
T05 4,800 86,400 3,070 95,200 1.56 0.91
T06 4,570 92,100 2,810 100,000 1.63 0.92
T07 5,830 137,500 3,220 94,400 1.81 1.46
T08 5,560 140,600 3,000 93,100 1.85 1.51
T09 5,270 120,500 2,870 89,500 1.84 1.35
T10 6,100 162,000 2,860 83,200 2.13 1.95
T11 5,140 160,400 4,180 112,100 1.23 1.43
T12 4,580 105,900 3,270 88,800 1.40 1.19
T13 3,840 96,000 3,500 109,500 1.10 0.88
T14 3,940 87,100 2,330 71,100 1.69 1.23
T15 4,390 98,200 2,570 70,100 1.71 1.40
T16 4,100 118,900 2,760 82,500 1.49 1.44
Mean 1.64 1.30
St<strong>and</strong>ard Deviation 0.29 0.28
The results of the comparison indicate that data from the weaker/softer material alone
is not sufficient to accurately predict the strength <strong>and</strong> stiffness of the combined materials.
Instead, the two test curves must be added mathematically <strong>and</strong> then the resulting strength
determined by the 5% offset method applied to the combined response curve.
Spring theory tests performed by Schmidt <strong>and</strong> Daniels (1999) used red oak base
material <strong>and</strong> white oak pegs. Schmidt <strong>and</strong> Daniels reported the mathematically combined
results to have, on average, a 0.4% larger yield value <strong>and</strong> 25.3% lower stiffness. A trend
of underestimating the stiffness when the base material is stiff is developed in both sets of
data. An explanation of this trend is not known.
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