As can be seen in Table 6, at the

proportional limit state, the SDR decreased from 1.50 to 1.46 as U increased from 50 mm to 200 mm, while at the stable state, the SDR increased from 1.76 to 1.84 as U increased from 50 mm to 200 mm.

The

proportional limit stress [Y.sub.tpb] and bending strength [F.sub.tpb] were obtained from the following equations:

here [[tau].sub.0] is shear stress at the initial semicycle, [[tau].sub.pl] and [[gamma].sub.pl] are the stress and strain of

proportional limit under torsion.

As presented in Table 1, maximum force causes stresses [sigma] = 376.2 MPa that exceed the

proportional limit of steel 20GL ([[sigma].sub.pl] = 231 MPa) (Daunys, Putnaite 2004).

The elastic limit is frequently indistinguishable from the

proportional limit in metals.

Modulus of elasticity (MOE), modulus of rupture (MOR), work-to-maximum load ([W.sub.ml]), work-to-proportional limit (elastic resilience, [W.sub.pl]), and fiber stress at

proportional limit ([S.sub.pl] were computed.

Investigators were most interested in the acoustic velocity response within wood that had been loaded into the range over and above the

proportional limit. Both stress and strain were recorded by the universal testing machine.

This includes the point on the curve where the relationship between stress and strain becomes non-linear; the so-called

proportional limit. While strains at yield typically range from 3% to 10% for most thermoplastics, the strain at the

proportional limit rarely exceeds 1% and for many materials it is less than 0.5%.

Samples of southern yellow pine outer bark and wood were tested in compression to determine values for modulus of elasticity, stress at

proportional limit, and maximum crushing strength.

This work is a part of a larger research effort to establish a usable computer program for the design of all timber to timber and timber to steel joint stiffness and

proportional limit strength.

The compressive properties such as Young's modulus,

proportional limit stress, and compressive strength were obtained from the stress-strain relation.

They cannot determine the shear stress/shear strain behavior including the shear modulus and shear stress at the

proportional limit. To determine these properties, the Iosipescu shear test is promising because the test can be done under the nearly pure shear stress conditions (ASTM 1998, Liu 2000b, Yoshihara et al.