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•The authors proposed a numerical model to analyse blast wave dynamics.•Study influence of pre-detonation shape of the high-explosive.•Study influence of mass of explosive.•Shape of ...explosive strongly influences blast wave dynamics and resulting pressure/impulse.
A numerical model is developed to analyse the influence of the shape of a high-explosive on the dynamics of the generated pressure wave. A Multi-Material Arbitrary Lagrangian Eulerian (MM-ALE) technique is used as the CONWEP approach is not adequate to model such situations. Validation and verification of the proposed numerical model is achieved based on experimental data obtained from the bibliography. The numerical model provides relevant information that cannot be obtained from the experimental results. The influence of the mass and shape of the high-explosive is studied and correlated to the dynamics of the generated blast wave through the analysis of peak pressures, time of arrival and impulse. Tests are done with constant mass hemispherical, cylindrical and flat-shaped Formex F4HV samples. A detailed analysis of the generated blast wave is done, along with a thorough comparison between incident and reflected waves. It is concluded that the dynamic effects of the reflected pressure pulses should always be considered in structural design, most relevantly when analysing closed structures where the number of reflections can be significant. The model is proved reliable, concluding that the frontal area of the high-explosive is a determinant driving parameter for the impulse generated by the blast.
A study of the impact behaviour and the post-impact residual strength of fully biodegradable composites is presented in this work. To this end, low-velocity impact tests and compressive residual ...strength tests were carried out on flax/PLA laminates. The results were compared with carbon/epoxy laminates, showing some important advantages in terms of absorbed energy and normalized residual strength. The reason was attributed to different energy absorption mechanisms; the main failure mode in flax/PLA laminates is fibre failure while residual strength of carbon/epoxy laminates is dominated by delaminations.
This work proposes the experimental study of an auxetic polymeric structure manufactured by 3D printing (SLA). The structure is composed by a re-entrant unit cell based on cylindrical elements not ...previously studied. The effect of the number and size/scale of the unit cells used in the specimens, subjected to both static and dynamic loads, has been analysed. The results show how the studied variables affect the behaviour of the structure in terms of stress and strain and that the dimensions of the cylindrical elements, as well as the contact between them, could help to modify the stiffness structure as required. The tests performed have allowed to understand the sequence of physical phenomena that appears at different strain rates and how they affect the response of the structure. The results obtained may contribute to the knowledge of both polymeric auxetic structures and the use of additive manufacturing methods for such structures.
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•Development of a 3D auxetic polymeric cell by means of SLA manufacturing technique.•Experimental study of a polymeric auxetic structure under different loading rates.•Effect of the cells´ number and size on the mechanical response of the structure.•The cylinder-based unit cell could lead to control the stiffness of the structure.•Analysis of physical phenomena in the auxetic structure at different loading rates.
•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.
In this work it has been characterized the impact behaviour of quasibrittle fragments against a Hopkinson bar in a wide range of impact velocities (70-180 m/s). Hopkinson bar is designed to measure ...the impact forces thanks to a proper instrumentation. In this case, semiconductor strain gauges, which sensibility is higher than common strain gauges, are used. Two material are studied to widen the range of applicability of the experimental facility: PMMA and a woven composite material. Moreover, two high speed cameras (Photron SA-Z) have been used to obtain the displacement and strain field of the fragment impactor using 3D Digital Image Correlation (DIC). A special technique has been used to print the speckle in the fragment based on previous works. The developed experimental methodology has shown the different failure modes that may happen in the fracture process when the quasibrittle fragments acts as the impactor providing a better understanding of its physical behaviour.
•A vibration-based approach for impact damage identification in CFRP is proposed.•Experimental validation realized with high-velocity ice impacts on CFRP laminates.•Conversion of whole response to a ...scalar indicator correlating with damage severity.•Residual load-bearing capacity have been quantified from spectral indicators.
This paper investigates the feasibility of using a novel domain-based correlation approach derived from the complex frequency domain assurance criterion (CFDAC) for the detection and quantification of impact damage in composite laminates. The CFDAC is essentially a complex-valued two-dimensional indicator of the covariance between two sets of frequency response functions for each pair of spectral lines corresponding to vibration-response of pristine and damage states. The study focuses on damage induced by high-velocity ice impacts on carbon fiber laminated plates. The experimental results demonstrate that the proposed methodology correctly identifies the level of induced damage via a user-independent scalar damage indicator. Therefore, this approach has potential use as a damage indicator, which could be adapted as a structural assessment non-destructive method. This research aims to contribute to the further development of functional, autonomous, and reliable structural health monitoring systems for composite structures based on spectral-domain indices.
•The main failure mechanism that appears in the composite fragments is laminate crushing.•A double cantilever beam opening process appears in all specimens impacted.•A simple analytical model is ...defined to predict the contact force, and the eroded mass.
This work analyses the impact against a rigid plate of carbon epoxy fragments. Experimental tests have been performed by means of a gas gun capable of launching rectangular pieces of composite laminates at a wide range of impact velocities (from 70 to 180 m/s). The impact process has been recorded using three high speed video cameras which allowed to analyse the phenomenon and to obtain the deceleration of the fragment and hence the force–time history and impulse induced on the plate. The failure process of the impacted fragments has been studied to identify the main absorption mechanisms and based on that a simple analytical model is proposed in order to predict the erosion and the impact force.
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•Low time-consuming identification of modal parameters using 3D DIC.•Comparison of results applying 3D DIC and a traditional experimental method.•3D DIC allowed obtaining much ...smoother mode shapes, useful for damage localization.•Drastically reduced discrepancies of updated parameters with measured ones.•Very similar results of model updating based on the two experimental methods.
Model updating is usually based on the contrast between the modal characteristics predicted by the models and those experimentally identified. Traditional experimental methods are based on the use of contacting sensors, but more recently other techniques as 3D Digital Image Correlation (DIC) have also been used successfully. In this paper the results obtained by applying these alternative techniques are compared, to obtain physically-sound models of carbon/epoxy composite plates. Primarily a roving hammer exciting the plates at evenly distributed degrees of freedom (DoF), and a mono-axial accelerometer attached to a single DoF reference point, have been used for modal identification. Alternatively, high speed cameras were applied to measure full-field vibrations of the plates. 3D DIC allowed obtaining a lower number of natural frequencies but much smoother mode shapes and similar results for model updating. The experimental setup has been benchmarked using two different sets of plates varying thickness and ply stacking.
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.
This work presents a methodology to obtain physically-sound models of composite structure laminates using a combination of modal analysis, numerical modelling and parameter updating, avoiding the ...common uncertainties on the constructions of similar numerical models. Moreover this model establishes the baseline (pristine situation) of the dynamic behaviour of the set of composite plates. Therefore it could be applied for condition assessment or quality manufacturing control of existing structures through a non-destructive Structural Health Monitoring (SHM), and hence it could help to detect degradation or defects of the composite components. The driven data of the methodology were the modal frequencies and shapes of composite plates. To obtain these values an extensive experimental campaign of modal analysis has been performed on a set of carbon/epoxy laminates. A multiple input single output technique has been applied, using a roving hammer exciting the plates at evenly distributed Degrees of Freedom (DoF), and a mono-axial accelerometer attached to a single DoF reference point. The use of a high dense grid of points has allowed to identify a number of natural frequencies greater than usual in similar works, as well as improving the smoothness of the mode shape. Modal characteristics numerically obtained from a Finite Element Method (FEM) model based on manufacturer reference data were compared with experimental results. This baseline model was updated through a gradient based optimization algorithm. Before the process of model updating, a sensitivity analysis has been performed to identify the driven uncertain parameters using a Montecarlo approach. This technique reduces the number of parameters to be optimized to a small set increasing the efficiency of the methodology. As a result of the whole process, a physically more accurate model is obtained on which discrepancies with the corresponding experimentally measured modal parameters are drastically reduced. Analysis of the consistency of the adjusted numerical parameters has been done with alternative experimental tests (Quasi Static Loading (QSL) and Ultrasonic inspection).
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