F. Gov

Bio: F. Gov is an academic researcher from Technion – Israel Institute of Technology. The author has contributed to research in topics: Acceleration & Beam (structure). The author has an hindex of 1, co-authored 1 publications receiving 31 citations.

Enhanced Evaluation of the Low-Velocity Impact Response of Composite Plates

Abstract: Recent research programs conducted on low-velocity impact events on composite structures have used force as the sole governing parameter and based their damage resistance and tolerance considerations on the peak recorded value. Understanding of other available parameters, such as contact duration and coefficient of restitution, which are related to the effective structural stiffness of the target, is fundamental in the design of a methodology for assessing impact performance and can offer greater insight in the interpretation of future research programs. An experimental database is gathered through drop tower impact testing by means of a rigid striker on clamped circular plates, for a particular polymer composite system. Several researchers have presented data showing that a critical value of the impact force for the onset of damage exists. Structural properties are hereby studied in both the sub- and supercritical regimes, which means for impact energy values below and above the damage threshold. A modified approach to the classic spring‐mass model, which employs the notions of damaged stiffness and dissipated energy, leads to the derivation of approximate formulas that describe the peak force-energy curve. In particular, the introduction of a dashpot to simulate the effect of damage greatly improves the accuracy of the model in the regime beyond the structural integrity threshold. A novel method to assess the residual performance of the damaged plate is developed, and it consists in low-energy, nondestructive impact testing, the results from which bear a striking resemblance with the curves obtained by compression after impact. MPACT tests can prove inherently difficult to understand because of the large number of parameters that play a key role in such events, particularly in the case of laminated composite structures due to their heterogeneous anisotropic nature and the complex failure modes that can occur. The current experimental investigation is conducted on square plates, supported over circular openings, having a quasi-isotropic [0/90/±45]4s stacking sequence. Such a configuration benefits from the axial symmetry of the circular geometry and the low degree of anisotropy of the laminate and thus facilitates the concentration on the mechanics of the impact event and the complex failure mechanisms. An extensive literature review has indicated that many questions still surround the impact response of composite plates. In particular, an ongoing debate exists on whether force or energy should be used to compare impact test results on different configurations, as well as whether a force- or energy-based criterion should be employed to predict the structural integrity threshold or uniquely and satisfactorily assess the state of damage in the plate. The aim of this paper is to show how governing parameters, such as force, energy, and structural stiffness vary between the subcritical and supercritical regimes and that peak force, although extremely valuable for predicting the damage threshold, cannot be used independently for investigating the impact performance of a composite structure. The use of an instrumented drop tower such as the General Re

Prediction of the impact force on reinforced concrete beams from a drop weight

Abstract: It is always a challenge to efficiently and accurately estimate the force on structures from falling objects. This study aims to predict the maximum impact force on reinforced concrete beams subjected to drop-weight impact using artificial neural network. A new empirical model including a comprehensive version and a simplified version is proposed to estimate the maximum impact force. The model was verified against a database collected from the literature including 67 reinforced concrete beams tested under drop-weight impacts. The database covers the concrete strengths ranging from 23 to 47 MPa, the projectile mass from 150 to 500 kg, and the impact velocity up to 9.3 m/s. The prediction of the comprehensive version of the proposed model fits the experimental results very well with an average absolute error of 11.6%. The simplified version of the proposed model is established for easy estimation, with the average error of 23.2% in prediction of the maximum impact force.

Some Recommendations for Characterization of Composite Panels by Means of Drop Tower Impact Testing

Abstract: Instrumented drop tower impact-test devices have been long used for inflicting impact damage onto test specimens for damage tolerance characterization of composite panels. However, there are many considerations that need to be made regarding the test setup to avoid the inconveniences related to the acquisition and interpretation of the impact data. Because there are many advantages associated with this type of experiment, to benefit fully from the amount of information available from an impact test, a multiparameter approach needs to be used, and the entire test history needs to be interpreted. The previously demonstrated similitude between impact and quasistatic indentation tests is used to gain even further understanding in the mechanics of the event and its associated damage mechanisms. The fundamental characteristics of damage resistance tests are illustrated for the engineer being initiated to this type of work, particularly with regards to the understanding of impact traces. A summary of lessons learned is reported, and guidelines for the setup of the test and the interpretation of the results are given. A set of recommendations for best practice is given with the intent of laying down the foundation for a standard approach to future research programs.