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Advanced mechanics of materials (1993-John Willey) Episode 11

Tham khảo tài liệu 'advanced mechanics of materials (1993-john willey) episode 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 582 14 STRESS CONCENTRATIONS Figure 14.16 Stress concentration factors obtained by use of the photoelastic method. 14.4 EXPERIMENTAL TECHNIQUES 583 only after considerable experience. In particular special care must be exercised to obtain trustworthy results when the radius of the notch is very small Kobayashi 1988 . Values of the calculated stress concentration factors obtained by the photoelastic method for three forms of abrupt changes in section in flat specimens are shown as reported by Frocht 1936 in Fig. 14.16. In each specimen the stress distribution is uniform at distant sections on either side of the abrupt change when the stress distribution is variable on either side of the abrupt change in section as in bending the calculated stress concentration factor is found to be somewhat smaller. These curves show that the value of Scc varies with the ratio p d. However Scc also depends on the ratio D d. For the particular groove hole and fillet shown in Fig. 14.16 the values of p d and D d are related by the equation D d 1 Ip d. The values of Scc for the hole and groove in Fig. 14.16 can be found also by Neuber s solution as obtained from Fig. 14.10 for various values of p d. These values obtained from Neuber s nomograph agree satisfactorily with those found by the photoelastic method. The elasticity solution for the calculated stress concentration factor for the fillet is achieved by a numerical method that is an approximation. Hence the photoelastic method is of special value for this type of discontinuity. For the fillet in Fig. 14.16 for which t p the curve marked t p gives values of Scc. For members in which t is not equal to p the values of Scc will be different as shown for example by the curve marked t 3p. The influence of t p on the values of Scc for a fillet subjected to axial tension and to bending has been studied by Frocht 1936 . The distribution of stress shown in Fig. 14.17 was obtained by Coker and Filon 1957 by the photoelastic method. The .