region at the ith cycle, and Atotal is the area of the overall sample re- gion under study。
By using of the Eq。 (3) we can plot the TDC over each fatigue test for the two specimens made of AWJ and one specimen made of CM (cf。 Fig。 12)。
From Fig。 12 we observe that, for all applied loads, TDC of spec- imens machined with AWJ are lower than TDC of specimens drilled with CM。 These results are in good agreement to that observed with extensometer (cf。 Fig。 3)。 However, regardless of the machin- ing process used and for the same load, the damage rates calcu- lated from the heat dissipation (Eq。 (3)) are larger than those calculated from the decrease of rigidity (Eq。 (1))。 Again, this is con- sistent with the findings of Toubal et al。 [35] where a direct corre- lation was observed between accumulated damage and surface temperature。 The TDC can thus be used to predict damage accumu- lation under a given fatigue-loading scenario。
3。2。4。Endurance Limit Investigation
In general, the endurance limit is obtained by Whöler curves (stress vs。 cycles)。 This endurance limit can also be obtained from the temperature stabilization curves [39,40] by intersecting the
two straight lines that interpolates the stabilization temperature (DT = Tf — T0) and the corresponding stress level。 The profile of DT at 5000 cycles for different loads for CM and AWJM specimens
is shown in Fig。 13。 As can be seen, the endurance limit of the spec-
M。 Saleem et al。 / Composites: Part A 55 (2013) 169–177 175
Areas considered for analysis
(a)(b) (c)
Fig。 9。 Temperature contours for AWJM specimens at 5000 cycles under (a) 3 kN, (b) 8 kN and (c) 11 kN cyclic loads。 Highest temperatures are in pink/violet and lowest are in black/dark blue。 The area around the hole within the rectangle is considered for investigation。 (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article。)
(a) (b)
failure
(c)
Fig。 10。 Temperature contours for CM specimens at 5000 cycles under (a) 3 kN, (b) 8 kN and (c) 10 kN cyclic loads。 The area around the hole within the rectangle is considered for investigation。 (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article。)
Fig。 11。 Curves of damage accumulation and temperature for an AWJM specimen over a lifetime of 5000 cycles。 (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article。)
Fig。 12。 Thermographic Damage Criterion (area fraction of the region of maximum temperature) at each cyclic loading level from 3 kN to failure。 (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article。)
imen drilled using CM (Fig。 13a) is lower than that of AWJM (Fig。 13b)。 The values of endurance limit for five conventionally
drilled specimens and five abrasive water-jet specimens are
83。3± 4 MPa and 93。5 ± 0。76 MPa respectively。 Based on the above
176 M。 Saleem et al。 / Composites: Part A 55 (2013) 169–177
regions of fiber pullout or thermal matrix damages were evident in the AWJM holes。 Surface roughness parameters (Ra and Sa) indi- cated that AWJM and CM holes have the same surface roughness values, although the type and the form of the damage generated by each machining process is completely different。 机械设计制造及其自动化英文文献和中文翻译(8):http://www.youerw.com/fanyi/lunwen_101654.html