“…For this reason, in this work a modified version of the CBT taken from literature is adopted. 10,29,30 The following expressions is used for the evaluation of the energy release rate in DCB and ENF…”
Section: Analytical Solutionmentioning
confidence: 99%
“…[7][8][9] A few researchers have studied fracture toughness in coupons with interface plies at different orientation using Double Cantilever Beam (DCB) specimens. Blondeau et al 10 tested several DCB specimens with anti-symmetric interfaces (h/-h), comparing the results to unidirectional specimens and obtaining a similar onset value of the fracture toughness for all lay-ups, while the R-curves differ with higher values of the fracture toughness found in the specimens with antisymmetric interfaces. Yao et al 11 also observed a similar onset value followed by a higher R-curve effect when comparing 0 � /0 � and 45 � /45 � DCB specimens.…”
The standard experimental procedures for determining the interlaminar fracture toughness are designed for delamination propagation in unidirectional specimens. However, in aerospace structural components, delamination usually occurs between plies at different orientations resulting in different damage mechanisms which can increase the value of the fracture toughness as the delamination propagates. Generally, numerical analyses employ the value measured at the delamination onset, leading to conservative results since the increase resistance of the delamination is neglected. In this paper, the fracture toughness and the R-curves of carbon/epoxy IM7/8552 are experimentally evaluated in coupons with delamination positioned at 0°/0° and 45°/−45° interfaces using Double Cantilever Beam (DCB) and Mixed-Mode Bending (MMB) tests. A simplified numerical approach based on the Virtual Crack Closure Technique (VCCT) is developed to simulate variable fracture toughness with the delamination length within a Finite Element code using a predefined field variable. The results of the numerical analyses compared with the experimental data in terms of load-displacement curves demonstrate the effectiveness of the proposed technique in simulating the increase resistance in delamination positioned between plies at 45°/−45° interface.
“…For this reason, in this work a modified version of the CBT taken from literature is adopted. 10,29,30 The following expressions is used for the evaluation of the energy release rate in DCB and ENF…”
Section: Analytical Solutionmentioning
confidence: 99%
“…[7][8][9] A few researchers have studied fracture toughness in coupons with interface plies at different orientation using Double Cantilever Beam (DCB) specimens. Blondeau et al 10 tested several DCB specimens with anti-symmetric interfaces (h/-h), comparing the results to unidirectional specimens and obtaining a similar onset value of the fracture toughness for all lay-ups, while the R-curves differ with higher values of the fracture toughness found in the specimens with antisymmetric interfaces. Yao et al 11 also observed a similar onset value followed by a higher R-curve effect when comparing 0 � /0 � and 45 � /45 � DCB specimens.…”
The standard experimental procedures for determining the interlaminar fracture toughness are designed for delamination propagation in unidirectional specimens. However, in aerospace structural components, delamination usually occurs between plies at different orientations resulting in different damage mechanisms which can increase the value of the fracture toughness as the delamination propagates. Generally, numerical analyses employ the value measured at the delamination onset, leading to conservative results since the increase resistance of the delamination is neglected. In this paper, the fracture toughness and the R-curves of carbon/epoxy IM7/8552 are experimentally evaluated in coupons with delamination positioned at 0°/0° and 45°/−45° interfaces using Double Cantilever Beam (DCB) and Mixed-Mode Bending (MMB) tests. A simplified numerical approach based on the Virtual Crack Closure Technique (VCCT) is developed to simulate variable fracture toughness with the delamination length within a Finite Element code using a predefined field variable. The results of the numerical analyses compared with the experimental data in terms of load-displacement curves demonstrate the effectiveness of the proposed technique in simulating the increase resistance in delamination positioned between plies at 45°/−45° interface.
“…In [ 8 ], resistance against delamination under Mixed-Mode loading (G II = 34%, 85%) was investigated for 0°//0°, 0°//22.5°, 0°//45°, and 0°//90° interfaces. More recent results of similar investigations can be found, e.g., in [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ], and in [ 19 , 20 , 21 , 22 ] where also R-curves were of interest.…”
Dependence of the initiation values of the Strain Energy Release Rate, GCi, on the orientation of the reinforcement direction α relative to the delamination front was investigated for two laminates of different interfacial ply arrangements. In the case of the first laminate, the delamination was located at the interface of the layers reinforced with symmetric fabric and unidirectional fabric. In the case of the second laminate, the delamination was located at the interface of layers reinforced with symmetric fabric. In both laminates, the orientation of fibers in the layers separated by the delamination differed by 45° regarding the warp directions. The investigations were carried out for Mode I, Mode II, and Mixed-Mode I/II (GII/GI = 1 and GII/GI = 1.7) loadings using hybrid beam specimens. The major problem appearing in the intended tests was the inevitable lack of symmetry in the xz and xy planes of the specimens and the resulting deformation and stress–strain couplings, causing undesired loading modes. To decrease these couplings, especially designed hybrid beam specimens were used. An auxiliary finite element analysis was performed to assess the remaining effects of the reduced couplings. To ascertain whether statistically significant differences between Gci values for different α occurred, the one-way analysis of variance supplemented by Levene’s test was carried out. The dependence of Gci on α was found out for both laminates. However, it was not equally strong, and it turned out that the loading mode and the interfacial ply were arrangement sensitive.
“…They differed in that the interlaminar crack started from the junction point and stopped somewhere close, instead of progressing to the end of the specimen as shown in Figure 7, highlighting the different interlaminar fracture properties. 25 For the S45/4 and S60/4 specimens, no holes or interlaminar fractures were observed. Figure 17.Typical tensile load–displacement curves of different stacking sequences with and without ply splicing.Figure 18.Fractographies of specimens after tensile tests.Figure 19.Tensile load–displacement curve with fractographies for S30/4.…”
Section: Resultsmentioning
confidence: 88%
“…They differed in that the interlaminar crack started from the junction point and stopped somewhere close, instead of progressing to the end of the specimen as shown in Figure 7, highlighting the different interlaminar fracture properties. 25 For the S45/4 and S60/4 specimens, no holes or interlaminar fractures were observed.…”
To fabricate large-scale or unusually shaped composite structures, pieces of reinforcement plies can be spliced to match specific size and shape requirements, forming ply splice structures. The junction of different plies can be considered a defect in the final material, affecting the mechanical properties. In this paper, ply splice carbon fiber reinforced plastics were studied to analyze the fracture mechanism caused by the ply splice, including the effects of the junction geometry and the ply angle. Tensile tests were performed, assisted with digital image correlation for strain distribution analysis and acoustic emission for break mode analysis. The finite element method was also performed using ABAQUS software to study the fracture mechanism. In order to analyze the interlaminar fracture, the interface was simulated with cohesive elements. The results showed that, for a unidirectional carbon fiber reinforced plastics with ply splice, fracturing occurred first at the junction location and then at the interfaces between the splicing layers and the continuous layers. The final strength was determined by the number of continuous layers. The ply-angle had evident effects on the properties of carbon fiber reinforced plastics with ply splices. For a stacking sequence of [± 30°]5S, the effects of the ply splice on the strength and the fracture mode were similar to the effect with unidirectional plates. For a stacking sequence of [± 45°]5S, the ply splice had no effect on the fracture mode, but it did decrease the strength slightly. For a stacking sequence of [± 60°]5S, almost no effect of the ply splice structure could be observed. PACS (optional, as per journal): 75.40.-s; 71.20.LP
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