INFLUENCE OF STRUCTURE SIZE IN LINEAR AND NONLINEAR (WOOD) FRACTURE-MECHANICS

Fracture mechanics models for assessment of load bearing capacity of (wood) structures imply an influence of structure size such that larger structures show lower capacities compared to smaller ones of alike shape. The size effect scale depends on whether principles of linear or nonlinear fracture mechanics (LEFM resp. NLFM) are adequate. Following a brief survey of linear fracture mechanics the LEFM size effect law is given and compared to Weibull theory. The necessity of an LEFM application limit along with smaller sizes is demonstrated. Next, basics of nonlinear fracture mechanics especially of strain softening materials such as wood are outlined and terms like fracture process zones and characteristic lengths are discussed. It is shown how Bazant's NLFM size effect law enables the link between classic strength approaches and linear fracture mechanics.