tailieunhanh - New Trends and Developments in Automotive Industry Part 9

Tham khảo tài liệu 'new trends and developments in automotive industry part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 270 New Trends and Developments in Automotive Industry Fig. 3. The SEM micrograph of the chipped surface of coating Lonyuk et al. 2008 . Before scratch After scratch Before scratch After scratch Fig. 4. Visual differences of automotive coating before and after scratching. Mechanical damages of these types may be caused by polishing equipments carwash bristles tree branches and sharp objects such as keys Tahmassebi et al. 2010 . Effects of Environmental Conditions on Degradation of Automotive Coatings 271 Scratch type The performance of automotive coatings is further complicated by nature of the created scratches which in turn is influenced by the viscoelastic properties of the clear coat itself and the conditions under which they are created. In this regard when an external stress is applied to coating there would be three different kinds of coating responses elastic deformation plastic deformation and fracture deformation Tahmassebi et al. 2010 Lin et al. 2000 Hara et al. 2000 . Elastic deformation has limited effect on the appearance of a coating therefore determination of plastic and fracture deformation seem more important. Some scratches are irregular and of a fractured nature Figure 5-a and may involve material loss while others are smooth Figure 5-b regular and involve plastic deformation of clear coats Lin et al. 2000 Ramezanzadeh et al. 2010 Jardret Morel 2003 Jardret Ryntz 2005 Jardret et al. 1998 . Fracture 1 Fracture 2 Plastic 1 Plastic 2 Fig. 5. SEM micrographs of two types of a fracture and b plastic scratches Tahmassebi et al. 2010 Ramezanzadeh et al. 2010 . Various parameters such as scratch force scratch velocity and environmental temperature would influence the type and form of scratch produced. There are many differences between these two types of scratches. First fracture types are irregular and may involve material loss Figure 5-a while others are smooth regular with no material loss Figure 5-b . The visibility of fracture-type scratches