Peridynamic Simulation to Fracture Mechanism of CBN Grain in the Honing Wheel Dressing Process

Regularly dressing of CBN honing wheel is an effective way to keep its sharpness and correct geometry during honing process. This study aims to understand the fracture mechanism of single CBN grain in the dressing process of honing wheel. The honing wheel dressing process was simplified into the dressing process of grinding wheel, and the bond-based Peridynamic method considering bond rotation effect was developed to investigate the progressive fracture evolution, stress characteristics, and fracture modes of CBN grains in this process. It was found that fracture evolution of CBN grains mainly underwent four stages: elastic deformation, damage initiation, crack formation, and macro fracture. In addition, the fracture initiation and propagation were mainly determined by the tensile and shear stress, where the former led to mode I fractures and the latter led to mode II fractures. The propagation of mode I fractures was stable while the propagation of mode II fracture was unstable. The results show that the Peridynamic approach has great potential to predict the fracture mechanism of CBN grain in the dressing process of honing and grinding wheels.

Features of the progressive destruction of bridge structures

The problem of safe maintenance of bridge structures in the event of emergency impacts is being considered. Also the problem of accounting for beyond-design-basis impacts on them is being discussed. Particular attention is paid to the problem of progressive fracture of bridges, which is practically not studied in our country. The equivalence of the problems of progressive fracture and survivability of engineering structures is discussed. An overview is given of a number of publications on bridge construction accidents with an analysis of the causes, which are divided into three groups: those caused by catastrophic natural events (60 per cent), caused by design errors and construction defects (30 per cent) and also caused by poor maintenance or excessive load (10 %). A.V. Perelmuter’s five theses on progressive fracture are being formulated: (1) The appearance of local failures of the designed system is quite possible; (2) The process of developing sequential destruction is the most dangerous of all possible; (3) Protection against progressive collapse is possible not only by bearing structures strength reservation of the construction, but on the basis of an analysis of the genesis of emergencies it is possible to propose other safety methods against progressive collapse; (4) When modelling the processes of progressive fracture, dynamic effects accompanying the removal of individual elements from the system should be taken into account; (5) If progressive fracture is unavoidable, ways should be sought to localize it and reduce its effects. At the end of the article, examples of progressive fracture of bridge structures due to the loss of sustaining capacity by the main members (due to corrosion cracking of the reinforcement) and owing to the partial fracture of some load-bearing elements of bridge superstructures are given. A conclusion is made on the need to organize scientific research on the progressive fracture of bridge structures.