Additions of particulate reinforcements in the polymer matrix are reported to improve the Interlaminar Shear Strength and Interlaminar Fracture Toughness of the composites.
Composite materials are prone to delamination as they are weaker in the thickness direction. Carbon nanotubes CNTs are introduced as a multiscale reinforcement into the fiber reinforced polymer composites to suppress the delamination phenomenon.
This review paper presents the detailed progress made by the scientific and research community to-date in improving the Mode I and Mode II interlaminar fracture toughness ILFT by various methodologies including the effect of multiscale reinforcement.
Methods of measuring the Mode I and Mode II fracture toughness of the composites along with the solutions to improve them are presented. The use of different methodologies and approaches along with their performance in enhancing the fracture toughness of the composites Interlaminar fracture major failure in polymer composites summarized.
The current state of polymer-fiber-nanotube composites and their future perspective are also deliberated. Introduction Composites laminates of carbon fiber reinforced plastic CFRP are generally created by aligning several sheets of CFRP or prepregs followed by curing and consolidation at the same time.
Therefore, the layers stick together and have extraordinary mechanical properties in the in-plane direction but still they are weaker in the transverse direction, which causes separation of plies under many different loading scenarios.
These defects are caused by either inter-ply defects due to overloads, intra-ply cracks, areas with high porosities, and poor adhesion at the ply interface. The inter-ply behaviour of a composite may have a direct say on the interlaminar fracture toughness ILFT and interlaminar shear stress distribution within the material.
Therefore, in designing the laminated composite structures, one of the limiting factors is the poor interlaminar strength.
The purpose of this study was to determine the influence of fibre architectures on the interlaminar fracture toughness and tensile toughness of flax fibre epoxy composites. The fracture toughness was investigated for both Mode I (GIC) and Mode II (GIIC) for seven flax-epoxy architectures: one plain weave, two twill 2 × 2 weaves, a quasi . Susceptibility to delamination is one of the major weaknesses of many advanced laminated composite structures. Knowledge of a laminated composite material's resistance to interlaminar fracture is useful for product development and . Interlaminar Fracture Toughness of CFRP Laminates matrix-dominated interlaminar regio n, brittle failure has been reported to manifest in the form of matrix Aside from the benefits that CNTss provide, their application in composites presents two major challenges: a homogeneous dispersion of CNTs inside th e polymer matrix and the oc.
Hence it is important to improve resistance to interlaminar fracture, which essentially means improved ILFT and researchers have given utmost attention in procuring ways to suppress or minimise the initiation and growth of delamination in laminated composites [ 12345678 ].
Failure analysis is essential to determine the nature of loading a composite structure that can be endured without damage.
There are three types of failure commonly observed in composites, viz; interlaminar, intralaminar, and translaminar, amongst which the interlaminar is the most common.
The interlaminar stresses cause plies or groups of plies in a laminate to separate from each other, leading to a phenomenon called, delamination. This initiates and propagates in the matrix layers intervening the reinforcement plies of the composite system, limiting their life and performance.
As the layers are stuck together by resin, the resulting bond provides the fracture path with low energy. Catastrophic damage without any external signs may also result from the undetected sub-surface interlaminar fracture. There is a tremendous loss of strength and stiffness due to interlaminar fracture which raises serious concerns about the safety and reliability of the composite structure.
This is a dominant obstacle in attaining the light weight potential of a composite material [ 91011 ]. The loading conditions are also different for all the three types of composite failures, viz.
Previous research pertaining to interlaminar fracture in composite materials has been reported by Garg et al. Delamination can occur when the applied load reaches the optimum and critical limit.
Different loading scenarios lead to opening, sliding, and tearing modes as far as fracture mechanics is concerned.
The parameter which is used to calculate the delamination resistance is the critical strain energy release rate Gc which is generally termed as interlaminar fracture toughness. The crack growth can be either a pure or mixed mode or even a combination of the both, but the delamination resistance requires the measurement of the critical energy release rate.
So, all the above-mentioned modes are required to be investigated to understand and predict the overall impact of delamination in the composites.
The above mentioned interlaminar fracture ILF features generated from different loading scenarios can be characterized effectively by carefully fabricating the composite laminates and applying the desired loading in a stable and controlled manner. As the crack direction is known for a particular loading, the fracture features can then be well documented.
Many test methods have been developed which are suitable for measuring the ILFT of the composite laminates. Recent findings leading to the developments of new standards of testing of interlaminar toughness were reviewed by Brunner et al.
In general, most standards are applicable for the unidirectional composites to predict and understand the fracture toughness under different modes of fracture. As per the literature [ 1617 ], double cantilever beam DCB and end notched flexure ENF specimens are more popular for quantifying Mode I and II delamination behaviour and these are highly effective procedures to evaluate the delamination resistance of these composite materials.
Many researchers have carried out a detailed study to propose the test method for a Mode III ILFT test, however, none of the testing standards has been widely accepted, so still, there is a lot of debate in recommending an efficient Mode III testing approach [ 15202122232425262728 ].
Although, Split Cantilever Beam SCB and edge crack torsion are the two prioritized methods which are widely used to compute the tearing mode details.
Factors Influencing the ILFT and Methods for Improving ILFT The growing demand for lighter and superior performance materials, especially in the area of aerospace, automobile, and defence applications has attracted the interest of many towards woven and unidirectional CFRP composites.
However, in spite of very good in-plane strength, they have poor resistance to interlaminar fracture under different loading conditions.
A lot of experimental and analytical research has gone into enhancing fracture toughness of laminated composite structures [ 2930313233 ].
Many factors can affect the ILFT value; the factors influencing the ILFT as found in the literature are material system, lamina stacking and laid up configurations [ 34353637 ], fabrication quality and fabrication procedure [ 383940 ], specimen thickness [ 41 ], and environmental effects [ 4243 ].
Among all, lamina stacking, laid up configurations, and fabrication procedure are the main parts of composite manufacturing and hence are the most important parameters to understand properly and to be discussed in detail here Refer Figure 2.
Considering the improvement of the ILFT, various hierarchical progression approaches adopted by researchers to impede the interlaminar fracture in composites as depicted as a flow diagram in Figure 2. Figure 2 shows that the first attempts were made to modify the matrix system with different fillers with an aim to improve the resin toughness.
This technique was followed with the changes in the fiber architecture as well as the surface modification so as to improve the thickness direction properties.
Interleaving and interlayer additions in between the fiber layers are also used as an interlaminar improvement mechanism. The methodologies used for enhancing the fracture toughness of composites are detailed in the following sub-sections.Susceptibility to delamination is one of the major weaknesses of many advanced laminated composite structures.
Knowledge of a laminated composite material's resistance to interlaminar fracture is useful for product development and material selection.
fatigue failure, laminated composites are, nevertheless, prone to failure by delamination. This laminated polymer composites in the through-thickness direction as a solution to problems of poor increase the interlaminar fracture toughness within. The fracture toughnesses associated with fibre tensile failure and compressive fibre kinking in a T/ carbon-epoxy laminated composite are measured using compact tension and ‘compact compression’ tests respectively.
Several mechanisms contribute to the composites’ interlaminar fracture toughness. An experimental study to validate tests used to determine mixed mode failure criteria of glass/epoxy composites. The analysis of interlaminar fracture in uniaxial fibre-polymer composites.
Knowledge of the interlaminar fracture resistance of composites is useful for product development and material selection. Since delaminations can be subjected to and extended by loadings with a wide range of mode mixtures, it is important that the composite toughness be measured at various mode mixtures.
Influence of water up-take on interlaminar fracture properties of carbon fibre-reinforced polymer composites R. SELZER, K. FRIEDRICH Institute for Composite Materials Ltd, University of Kaisersfautern, Kaiserslautern, FRG a new-generation resin with a higher strain to failure and a higher fracture toughness.