Stress-strain relationship of common wire nails under reversed cyclic loading

Nailed timber joints are known to play an important role in the performance of light timber frame structures under extreme loading conditions such as those caused by hurricanes and earthquakes. Numerical modeling of nailed joint response to these loading conditions requires knowledge of, among other things, the load-displacement or stress-strain property of nails under reversed cyclic load. As part of an overall program of work to validate a finite element nailed joint model, a new test method was developed and a modified constitutive material model was adopted to characterize the through-zero cyclic stress-strain behavior of nails of different diameters. Four nail diameters ranging from 2.78 to 4.08 mm were evaluated using the proposed cyclic test and the conventional monotonic tension test methods. It is noted that the proposed constitutive model provides an excellent representation of the cyclic response of the nails. A comparison with monotonic test data reveals that yield stress under cyclic loading is higher than the corresponding monotonic test response, but the ultimate strength appears unaffected. Under cyclic loading the so-called Bauschinger and strain-softening effects are clearly evident. Elastic moduli are similar for the four nails tested. However, yield stress and strain reduce with any increase in nail diameter. The area enclosed by a hysteresis loop increases with increasing nail size.