Nhiều chương trình CAD hiện nay cho phép tạo ra các mô hình ba chiều để có thể nhìn từ mọi góc độ. Các chương trình CAD mô hình hóa vật thể đặc tiên tiến là một hệ thống thiết kế hiện thực ảo. Những mô hình đặc như vậy có thể được dùng làm cơ sở cho các phân tích phần tử hữu hạn (FEA) và / hoặc tính toán động lực dòng chảy (CFD) của thiết kế. Cho đến ứng dụng gia công với trợ giúp máy tính (CAM), những mô hình này cũng có thể được dùng. | Modern Automotive Gear Oils - Classification Characteristics Market Analysis and Some Aspects of Lubrication 319 a b Fig. 28. Average concentration of sulfur and oxygen in the surface layer of the wear track for the oxidised gear oils a GL-3 oil b GL-5 oil In case of the oxidised GL-5 oil in the surface layer of the wear track a steady rise in the sulfur concentration takes place although it is rather small Fig. 28 b . A beneficial role of sulfur compounds has been mentioned earlier so it may be a reason for fatigue life improvement observed for the oxidised GL-5 oil Fig. 27 b . The rise in fatigue lives given by the oxidised GL-5 oil can also relate to a decrease in the lubricating additives in the oil due to precipitation of their oxidised products. The symptoms of additives decrease in the oxidised GL-5 oil are threefold drop in TAN for the longest oxidation time Fig. 18 b as well as nearly threefold drop in the area under the peak at 965 cm-1 in the IR spectrum Fig. 20 . The beneficial action of EP additives decrease is explained below. EP type lubricating additives used in GL-5 gear oils are known for their high corrosion aggressiveness. It leads to creation on the lubricated surface numerous depressions and micropits due to corrosive wear being potential nuclei for bigger macropits . In this way the chance of failure increases hence the fatigue life lubricated by EP additives tends to be reduced Torrance et al. 1996 . So unlike in case of the oxidised GL-3 oil the EP additives decrease in GL-5 oil due to oxidation exerts a beneficial influence on the surface fatigue life. Like in case of the water contaminated oils an adverse role of hydrogen embrittlement should not be neglected in case of oxidised gear oils. 7. Summary and conclusions Scuffing tests The contamination of the automotive gear oils of API GL-3 and GL-5 performance levels with the test dust practically does not affect their extreme pressure properties. 320 New Trends and Developments in .
