復(fù)合材料與工程外文資料翻譯--環(huán)氧樹(shù)脂的力學(xué)性能（原文）

1、JOURNAL OF MATERIALS SCIENCE 15 (1980) 1823-1831 The mechanical properties of epoxy resins Part 2 Effect of p/astic deformation upon crack propagation SALfM YAM INI, ROBERT J. YOUNG Department of Materials, Queen Ma

2、ry College, Mile End Road, London E1 4NS, UK Crack propagation in a series of epoxy resins described in Part 1 has been studied as a function of testing rate and temperature. It has been found that crack propagation is c

3、on- tinuous at low temperatures but that as the temperature is raised the mode of propa- gation becomes unstable (stick/slip). Features on the fracture surfaces at the crack arrest lines have been shown to be of the sa

4、me dimensions as those expected for a Dugdale plastic zone. It has been suggested that the “slip“ process takes place by slow growth of a crack through the plastic zone followed by rapid propagation through virgin mater

5、ial. It has been shown that the stick/slip behaviour is due to blunting of the crack which is con- trolled by the yield behaviour of the resin. A unique fracture criterion has been shown to be applicable to epoxy resins

6、which is that a critical stress of the order of three times the yield stress must be achieved at a critical distance ahead of the crack. Electron micro- scope replicas of the fracture surfaces have been obtained and an

7、underlying nodular structure can be resolved. However, no direct correlation between the nodule size and fracture properties has been found. 1. Introduction There is currently a great deal of interest in the mechanisms o

8、f crack propagation in brittle poly- mers. The general subject of crack propagation in thermosetting polymers has been reviewed re- cently by one of the authors [1] and this particu- lar paper is concerned with the propa

9、gation of cracks in epoxy resins. In certain polymers such as polymethylmetha- crylate (PMMA) cracks tend to propagate in a stable, continuous way through a constant crack- opening displacement (8c) criterion [2, 3], wh

10、ere- as in other polymers such as epoxy resins [4], crack propagation tends to occur in an unstable stick/slip manner. It is known [5] that unstable propagation is suppressed in epoxy resins if the cracks are propagated

11、at low temperatures, when the material is well below its Tg. It has been shown recently [6] that under these conditions a con- stant 6 e criterion also holds for an epoxy resin. It has been recognized for several years t

12、hat there is a relationship between the crack propagation be- haviour and the plastic flow properties of an epoxy resin [6, 7] but it is only very recently that 0022-2461/80/071823-09502.90/0 quantitative theories have b

13、een developed to ac- count for this relationship. Following a suggestion from Williams [8], the authors have been able to show that stick/slip propagation in one particular epoxy resin system could be explained through a

14、 crack blunting mechanism [9]. The same approach has been developed more formally by Kinloch and Williams [10] who found that the crack blunting mechanism could successfully explain the modes of crack propagation in a wi

15、de variety of epoxy resins. The plastic deformation of a series of epoxy resins has been carefully investigated in Part 1 and explained in terms of current theories of plastic deformation in glassy polymers. In this seco

16、nd paper the relationship between the flow behaviour and crack propagation has been analysed in detail as a function of the amount of curing agent used with the resin and post-cure temperature. 2. Experimental The epoxy

17、resin used in this study was Epikote 828 hardened with different amounts of triethy- lenetetramine (TETA) and cured for 3h at dif- ?9 1980 Chapman and Halt Ltd. 1823 Figure 2 Fracture surfaces of an epoxy resin cured w

18、ith 9.8 phr TETA. The specimen was post-cured at 50 ~ C for 3 h and tested at a cross-head speed of 0.05 mm rain -~ at 22 ~ C. (a) Optical micrograph of surface. (b) EM replica of crack arrest line. (Crack growth di

19、rection indicated by arrows). at room temperature. Fig. 3a shows that the specimen has a fine arrest line. The electron micro- graph in Fig. 3b shows the arrest line at a higher magnification. It can be seen that the str

20、ucture is again streaked and the arrest line corresponds to an abrupt change in direction of the streaks. There appears to be an underlying nodular structure of the scale of ~ 500 A. A good example of a broader type of c

21、rack arrest line is given in Fig. 4a. This type of feature is typical of well cured specimens fractured at tem- peratures close to Tg [7]. The fracture surface is featureless until the crack arrest point. After crack arr

22、est there is a slow growth region [13] of closely spaced striations parallel to the crack growth direc- tion. Following the slow growth region there is a rougher hackled region where the crack accelerates during the “sli

23、p“ process. Examination of the frac- ture surface by EM replicas has shown that the smooth areas of such specimens are relatively featureless in contrast to the slow-growth region which is shown in Fig. 4b. In this area

24、there are V-shaped features which appear to be caused by the crack propagating on different levels. It was not possible to resolve any underlying nodular structure on the specimen used in Fig. 4. 3.3. Slow-growth region

25、It was pointed out in the previous section that in well-cured specimens fractured at high tempera- tures there is a characterisitc region of slow crack growth which was first identified by Phillips et al. [13]. It is fou

26、nd that the size of this region, /r, increases as the temperature of testing is raised. This can be seen clearly in Fig. 5 for a resin con- taining 14.Tphr TETA, where micrographs are given for specimens which have been

27、fractured at two different temperatures. It was shown in Fig. 1 that for this formulation the critical stress inten- sity factor for crack initiation Kxci also increases Figure 3 Fracture surface of an epoxy resin cured

28、with 9.8 phr TETA. The specimen was post-cured at 100 ~ C for 3h and tested at a cross-head speed of 0.05 mm min -~ at 22 ~ C. (a) Optical micrograph of fracture surface. (b) EM replica of crack arrest line. (Crack g