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.
•A simplified Artificial bird has been proved to behave as literature review studies.•Radial expansion of the artificial bird has been studied.•Induced force by the impact has been measured using a ...Hopkinson tube.•The four numerical models benchmarked reproduce the impact force measured.•Numerical models commonly used are not capable to predict the radial expansion.
This work shows a combined experimental-numerical research in bird impact. In order to perform the experimental tests, a artificial bird has been prepared and impacted against a Hopkinson tube in a wide range of impact velocities (70–200 m/s). The Hopkinson tube was designed in order to measure the induced force transmitted in the tube by the impact. This force could be used to compare different experimental tests and also to validate the numerical models proposed. In addition, the whole process of impact was recorded by means of high speed video cameras. The images captured allow to perform the analysis of the bird kinematics during the impact. Numerically, in order to reproduce the high deformations experienced by the artificial bird in the impact process, the Smooth Particle Hydrodynamics (SPH) technique has been used. Concerning the artificial bird material behaviour, four different models were employed, combining the two material models and two equations of state most used in the literature. The four cases have been compared with the experimental measurements and benchmarked. After the analysis of the results, it can be concluded that the combined experimental-numerical methodology proposed successfully can be used to study and validate the numerical models for simulating the behaviour of soft impactor when subjected to high velocity impacts. It can be seen that the normal impact forces induced by the impact are reproduced adequately for all the numerical models. However the radial spreading of the soft impactor is not reproduced as adequately as the other cases, especially in low velocity impacts. This effect can be important to reproduce the radial distribution of pressures and the secondary impacts produced by this radial expansion.
A finite element numerical model for carbon/epoxy woven laminates has been used to predict residual velocity and damaged area when subjected to high impact velocities. Experiments using a gas gun ...were conducted to investigate the impact process and to validate the model, measuring the two variables previously indicated. A morphology analysis was also made to investigate the different breakage mechanisms that appear during the penetration process. The influence of the impact velocity and obliquity has been studied using the numerical tool, in a wide range of impact velocities and considering two impact angles, 0° and 45°.
The present study numerically investigated the use of bimetallic tubes for concentrating solar energy applications. Specifically, a billboard receiver employing supercritical carbon dioxide (sCO2) as ...the heat transfer fluid is considered, with tubes made of stainless steel 316 and GRCop-84. Two- and three-layer tube configurations are compared, exploring the impact of more thermally conductive layer thickness and placement on temperature and stress fields. The findings demonstrate that the use of bimetallic tubes can effectively reduce temperature and stress in the receiver tubes. In light of the results, it can be concluded that the higher thermal conductivity of GRCop-84 leads to a more uniform temperature distribution, resulting in lower temperature peaks on the outer tube surface, and reduced maximum stresses. Furthermore, it has been found that the incident heat flux necessary to achieve the same temperature increment of sCO2 inside the panel is 1.7% lower in a two-layer tube configuration where GRCop-84 is placed in the outer layer. Besides, the stress in the 316 layer can be reduced up to 53.2% with the cited configuration. Nevertheless, it is observed that it is more beneficial to tube performance to place the more conductive layer inside, since it reduces stress in the GRCop-84 layer, and its compressive stress and corrosion-resistant properties help to avoid the risk of stress-corrosion-cracking. In a three-layer composite tube configuration, placing the more thermally conductive GRCop-84 layer close to the outer tube wall decreases the maximum temperature while increasing stress. The opposite effect is achieved by placing the more conductive layer closer to the inner tube wall. Overall, the results demonstrate the potential benefits of using bimetallic tubes for solar energy applications, when the layers have similar thicknesses, since their use can enhance the thermomechanical performance of conventional tubes made with one layer of 316 stainless steel. This fact has important implications for the design of efficient and reliable solar thermal systems.
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•New concept of flat-external tubular receiver with bimetallic composite tubes.•Two- and three-layer tubes reduce temperature, heat losses, and stress.•Copper alloy layer reduces temperature and uniformizes heat distribution.•Inner copper layer may prevent stress corrosion cracking and carburization problems.•Asymmetrical layers impact thermal and mechanical performance of 3-layer tubes.
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.
•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.
In this work a constitutive relation for ice at high strain rates and an algorithm for its numerical integration are developed. This model is based on the Drucker–Prager plasticity criteria, which ...allows a different behavior in tension and in compression. In addition a failure criteria, based on pressure cut-offs, is implemented to describe the ice damage. In order to validate the constitutive model, numerical simulations were compared with experimental results, in which ice cylinders were impacted against a steel plate, allowing the measurement of the contact load. Three different numerical solvers are used in order to analyze its performance to appropriately modeling the ice behavior.
In this work, the analysis of the impactor mass effect on the behaviour of carbon/epoxy woven laminates under low velocity impact is carried out. To this end experimental test were performed by means ...of a drop weigh tower in a range of energies varying from 10 to 110J, and using three different impactor masses. Two different laminate thicknesses were considered in order to take into account its possible influence. An analysis of the impact tests is performed using the Composite Structure Impact Performance Assessment Program, in order to observe the influence of impactor mass. Once impacted, the laminates were inspected by means of a C-Scan (to quantify the delamination extension) and a phased array ultrasonic system (to analyse the failure through the thickness); this non-destructive analysis will determine the influence of the impactor mass on the laminate failure.
Hydrodynamic ram (HRAM) is a phenomenon that occurs when a high-kinetic energy object penetrates a fluid-filled container. The projectile transfers its momentum and kinetic energy through the fluid ...to the surrounding structure, increasing the risk of catastrophic failure and excessive structural damage. This is of particular concern in the design of wing fuel tanks for aircraft since it has been identified as one of the important factors in aircraft vulnerability. In the present paper, the commercial finite-element code LS-DYNA has been used to simulate an HRAM event created by a steel spherical projectile impacting a water-filled aluminium square tube. Two different formulations (ALE and SPH) are employed to reproduce the event. Experimental tests which indicate the pressure at different points of the fluid, displacement of the walls and cavity evolution for different impact velocities are compared with the numerical results in order to assess the validity and accuracy of both ALE and SPH techniques in reproducing such a complex phenomenon.
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