CFRPs drilling is a common process in the aerospace industry carried out prior to components assembly. Machining induced damage leads to significant percentage of component rejection. Damage ...extension strongly depends on drilling geometry and cutting parameters. Fresh drill geometry changes with cutting time due to the wear progression and the risk for hole quality is enhanced as cutting progresses. The influence of wear on hole quality has been analyzed in the literature using mainly an experimental approach.
Simulation of drilling process is an effective method that can be used to optimize drill geometry and process parameters in order to control hole quality and analyze the drill wear evolution. In this paper a finite element model for drilling woven CFRPs, reproducing both fresh and worn tools, is presented. Two different point angles considering fresh and honned edge were modeled. A progressive intra-laminar failure model based on the Chang and Chang model is considered. Cohesive elements allowed the analysis of inter-laminar damage (delamination). The model demonstrated its ability to predict thrust force and delamination for different values of feed rate and cutting speed. Model predictions show the influence of tool geometry (including variations induced due to wear) on delamination.
The cutting tool geometry is known to be an influential factor on damage induced during drilling of composite materials. Conversely, the geometry of the tool is affected under multiple drilling ...cycles due to highly abrasive nature of fibers. Building on earlier reports, the aim of this work is to create a better understanding of cutting parameters on the quality of drilled woven carbon fiber reinforced polymer (CFRP) laminates, given different tool wear conditions. Namely, a full factorial design of experiments has been conducted to quantify the significance of each process parameter (cutting velocity, feed rate and tool point angle), as well as their interactions, on the generation of entry- and exist- delaminations as well as the thrust force for different tool types. Finally, using a response surface methodology, a multi-objective optimization strategy has been presented to select optimum ranges of design parameters that can minimize the aforementioned output variables collectively. Such knowledge may be useful to explore further improvements toward defect-free drilling of woven CFRP composites.
This paper focuses on the influence of the step drill bit geometry on the damage induced during drilling Carbon Fiber Reinforced Polymer materials (CFRPs). Step geometry designed with the aim of ...avoiding composite damage in CFRPs drilling, is compared to conventional twist configuration. Despite the reduction of thrust force and torque observed when using the step drill, the delamination was only reduced at low feed rates. A numerical model developed for the step geometry was validated with experimental data demonstrating its ability to predict thrust force and delamination for different values of feed rate and cutting speed. Numerical model allowed the development of a parametrical study. Finally, using a response surface methodology a mechanistic model and surface diagrams have been presented in order to help in the selection of optimum variables minimizing drilling induced damage.
•Modeling of drilling of CFRPs involves elevated computational cost.•Simplified models lead to reduced computational time.•Complete and simplified models were compared in terms of delamination ...prediction.•The simplified model, slightly overestimates the delamination factor.•The influence of thrust force, clamping area and the stacking sequence is studied.
Delamination is one of the undesired effects of machining using non appropriate cutting parameters or worn drill. Finite element modeling of drilling of Carbon Fiber Reinforced Polymer (CFRP) composites is an interesting tool for damage prediction. Recently, complete modeling of the process including the rotatory movement of the drill, penetration in the composite plate and element erosion has been developed in the scientific literature. Computational cost of these complex models is a great disadvantage when comparing them with simplified models that consider the drill acting like a punch that pierces the laminate. In this paper both complete and simplified models were developed and compared in terms of delamination prediction. The simplified model, presenting reduced computational cost, slightly overestimates the delamination factor when compared with the complex model. The influence on delamination of thrust force, clamping area at the bottom surface of the laminate and the stacking sequence is studied using the simplified model.
The cutting tool geometry is strongly influencing damage induced during drilling of composite materials. The searching of new and optimum geometries reducing the damage on the laminates is still a ...challenge for the scientific community and industry. This study focuses on drilling woven CFRP laminates with four different tool geometries, analyzing the influence of the cutting parameters on the cutting forces and delamination damage. The work is divided in three phases; the first phase carries out a full factorial design of experiments conducted to quantify the significance of each process parameter as well as its interaction, on the generation of delamination at the hole entry and exit as well as the thrust force and torque. The second phase uses the response surface methodology (RSM) to establish the relationships between each output variable and the input variables based on ANOVA results. Finally, a multi-objective optimization strategy has been presented using the fitting equations to select optimum ranges of design parameters that can minimize collectively the aforementioned output variables. Ultimate objective is the process improvement toward negligible defects during drilling of woven CFRP composites.
In this work, seven different types of fabrics based on para-aramid yarns with different interlacing geometries and reinforcement polymer matrix have been characterised and compared from yarn level ...to weave level. Mechanical properties such as maximum stress, failure strain, and elastic modulus have been obtained from uniaxial tensile tests, while the inter-yarn friction coefficients (static and kinetic) have been obtained by a combination of single yarn pull-out tests and an analytical model. Results show that mechanical properties are quite similar at yarn level but different at fabric level. Thus, the geometry, orientation and section of the yarn play an important role in the mechanical properties of the fabric. As an application of these results, a mesoscopic three-dimensional numerical model has been developed, and simulations of ballistic impact test have been carried out validating the model with experimental tests.
Induced damage during biocomposites drilling is significantly different to that produced on composites based on synthetic reinforcement such as carbon or glass fibers. In composites reinforced with ...carbon or glass fibers, induced damage increases with feed rate, however damage was observed to decrease with feed rate in biocomposites reinforced with natural fibers. This work is focused on the explanation of this differences between biocomposites and traditional composites based on the effect of strain rate on the material behavior during machining. A FEM model has been developed in ABAQUS/Explicit to verify this hypothesis. This numerical model has been used to explain the differences found between traditional composites and biocomposites in the influence of the main drilling parameters on induced damage during drilling. Experimental tests were conducted to validate the model through the comparison between thrust forces and damage factor for two different drills geometries on Flax/PLA bio composites. The results indicate that the decrease of induced damage with feed rate is only predicted when the constitutive model accounts for experimental behavior observed in this type of composites. Additionally, the numerical model demonstrated the ability to reproduce the effect of the different cutting conditions (cutting speed, feed, thickness and drill geometry) observed during experimental tests on induced damage during drilling.
Machining processes of Carbon Fiber Reinforced Polymer (CFRP) are commonly required in order to achieve final assembly specifications. Despite the good mechanical properties of this kind of ...materials, they are hard to be machined due to the presence of hard particles; delamination, fiber pull-out and matrix thermal degradation are usually observed during its machining. Drilling operations are required before mechanical joining of the CFRP components. The actual interest in reducing delamination rests in the fact that it is the most serious damage found during drilling. In this work, a comparative study of three special geometries under different cutting conditions is presented. Thrust force and torque were monitoring during drilling tests and delamination extension was quantified. Results showed that a good drill tip geometry and feed rate selection is fundamental to reduce delamination damages.
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