The Structural Conservation of Panel Paintings

546 Richard, Mecklenburg, and Tumosa

Figure 22 shows the calculated bending stresses of oak panels of

different sizes and thicknesses subjected to 50-G topple impacts. These

panels are assumed to be supported on the parallel-to-grain edges only,

and the topple is a rotation of one ofthose edges. For this test, it is also

assumed that there are no battens or cradles attached to the reverse, since

they would provide a certain degr ee of bending protection.

Panels constructed of lighter woods such as pine (Pinusspp.;

specific gravity, 0.34) will develop comparatively lower bending stresses

when subjected to a 50-G topple impact. However, the strength of the

0 20     40  60  80  100

Station (cm)

Be

nd

ing

str

es

se

s(

MP

a)

6 5 4 3 2 1 0

3 1 Richard fig 21 eps

Figure 21
Distribution of the calculated bending stresses
for a 2.54 cm wide strip ofa 100 3150 3 2.54
cm thick panel subjected to a 50-G topple
accident. The bending stresses of panels sub-
jected to topples can be quite high, and in this
case they reach about one-half the breaking
stress of oak in the tangential direction.
Thinner panels are at even greater risk.

0 20     40  60  80  100     120

Cross-grained width (cm)

Ma

xim

um

be

nd

ing

str

es

s(

MP

a)

17

16

15

14

13

12

11

10

9 8 7 6 5 4 3 2 1 0

31 Richard fig 22 eps

1.25 cm thick

2.5 cm thick

Breaking strength 1.9 cm thick

Figure 22
Calculated maximum bending stresses for
white oak panels ofdifferent thicknesses and
sizes when subjected to 50-G topple accidents.
These stresses assume that the panels are sup-
ported only on the two parallel-to-grain edges.