Effect of Mechanical Load on Charring Rate of Wood in a Fire: An Atomistic and Experimental Approach

Description

While research on fire behavior and fire protection in timber buildings has beenconducted extensively for the wood pyrolysis, decomposition and charring, the questionof how the loaded condition of a structural wood member affecting the charring rateremains unanswered. In particular, little is known with regard to the assistance of themechanical stress towards the char formation, which eventually destroys the material.Prior research studies in this area have indicated the charring process of wood is verycomplicated. The timber decomposition are usually analyzed as two phases involvingprimary reaction of base wood pyrolysis and second reactions of resulting decompositionproducts. However, most pyrolysis models are empirical in nature and the decompositionof different constituents of wood is not fully considered. In addition, these existingempirical models on thermal decomposition pertain to the test environment at standardtemperature regime of timber construction in no-load condition, while most of thetimber structures are loaded when attacked by fire. Through the development of nano-engineeringand material modeling technique, molecular dynamics simulation is capableto reveal the decomposition of the wood constituents from an atomistic perspective, aswell as to predict the mechanical behavior of different constituents in a fire.The objectives of this research are to develop a reliable full atomistic model which canaccurately describe wood cell wall, and to study the effect of mechanical load on thecharring rate at an atomistic level using molecular dynamics simulation equipped withreactive forcefield (validated by bench-scale and medium-scale fire tests), as well as todevelop a predictive model that can fundamentally describe the wood pyrolysis. It isproposed to investigate by means of a synergistic effort consisting of hierarchicalmodeling of wood structures (i.e. cellulose, hemicellulose and lignin), reactive moleculardynamics simulations upon charring, experimental fire testing leading to theidentification of the pyrolysis products, integration of simulation and the experimentalresults to establish the reliable predictive model of charring process. Synergizing theknowledge developed in these research tasks, this study will form the basis foraugmenting existing design specifications for wood structures by including thequantitative fire protection design provided by the char layer. It is envisioned that theknowledge of the thermal decomposition of various wood species and the formation ofvarious pyrolysis products are crucial for further developing effective fire protectionmethods for timber-based materials, and for understanding the relative rating of theirflammability and fire safety.?