I would like to pay my respects to mr. Debnath demonstrates in the development of the shock and impact test simulator. The first part of the research is devoted to the development of the shock and impact test simulator at IIT Guwahati.
Introduction
Background
- Motivation
- Blast loading
- Structural design considerations
- Sacrificial protective system for blast and impact mitigation
Blast loading usually occurs on the outer envelope of the structure, while seismic loading results in base excitation. me). The magnitude of the shock wave depends on a) the explosive (type, amount), b) the distance and c) the confining boundaries (air/ground/rigid boundaries) that cause the blast to amplify.
Methodology and objectives of the thesis
Organization of the thesis
The primary purpose of the sacrificial protective covering is hierarchical plastic deformation to absorb maximum ballistic energy and thereby transfer residual energy to the primary structure. The classification of the dissertation chapters, together with the activities, results and future work, is detailed in Figure 1.8.
Literature review
Overview
Previous research on blast and shock loading
UFC gives the different blast charge categories and the estimation of the blast parameters of some common explosives. Empirical formulas for predicting the blast loads have been proposed for the design of the structure.
Previous research on blast and shock loading on reinforced concrete (RC)
The use of long carbon fibers significantly increased blasting performance and minimized crack size in the panels. They considered two variants in the sample configuration, namely compact reinforced concrete (CRC) columns and ultra-high performance fiber reinforced concrete (UHPFRC) columns.
Previous research on seismic behavior of beam-column joints
The equilibrium of the beam-column sub-assembly and the equilibrium of the joint panel are shown in Figure 2.12. Most of the beam-column joints in the existing structures had either non-seismic or seismic details.
Previous research on impulse loading on honeycomb protected structures
- Impact dynamics and contact law
- Impulse response of honeycomb composite
- Low-velocity impact studies on sandwich structures
- High-velocity impact studies on sandwich structures
Based on the contact ratio, they proposed the analytical models for the quasi-static and dynamic behavior of the sandwich panels to evaluate the impact force when subjected to low-velocity impacts on sandwich panels. They observed that the failure mode of the honeycomb sandwich beam subjected to cyclic bending was decomposed between the face skin and the adhesive. They successfully predicted the impact energy absorption of the sandwich panel and the extent of impact damage.
Predicted sandwich panel impact energy absorption and impact damage rate.
Summary of literature review
Development and characterisation of shock and impact loading
Introduction
Fundamentals of blast loading
- Explosions
- Blast-loading categories
- Explosion phenomenology
- Blast parameters
A typical blast event showing the shock wave and its fireball (heat) and the blast wave propagation schematic are shown in Figure 3.1. The magnitude of the reflected pressure depends on the shape of the target object and its orientation with respect to the blast wave (Naito et al. 2006). The impulse is classified into positive and negative, based on the corresponding phase of the blast wave time history.
The air behind the shock front of the shock wave travels in the same direction of the wind at a lower speed.
Fundamentals of shock loading
- Generation of shock wave
- Driver section
- Diaphragm section
- Driven section
- Driver and driven section support
- Protection chamber
Furthermore, the calibration of the shock tube and its characterization are emphasized in the subsequent sections. The pressure variations over the length of the shock tube can be seen in Figure 3.7. The conceptual figure of the shock tube and various stages of experimental setup are shown in Figure 3.8.
It combines to form a powerful shock wave in the driving part that propagates towards the driven part and leads to the end of the shock tube.
Characterisation of shock wave profile
- Membrane burst characteristics
- Shock wave characterisation
- Experimental results and discussion
- Numerical analysis of shock tube
It was observed that the increase in the thickness of the diaphragm membrane increases the burst pressure and peak over pressure of shock wave linearly. For the calibration of the shock tube setup, numerous experiments were performed with different Mylar membranes. For the present experimental investigation (results presented in Chapter 4, Section 4.2.2), the diaphragm consists of 5 Mylar membranes.
The computational domain of the shock tube is modeled as an axisymmetric body and the associated initial boundary conditions are illustrated in Figure 3.20.
Experimental and analytical investigation of an exterior reinforced
Introduction
2016) performed finite element analysis to investigate the influence of the shear and diagonal reinforcement on the blast resistance of beam-column connections. Limited investigations have also been conducted on the performance of beam-column connections under blast loading, which is. The key motivation of the present research is to study the behavior of a beam-column subassembly subjected to shock wave loading.
In this study, the dynamic response of the external beam-column connections with deficiencies such as weak beams in bending, weak beams in shear and weak columns in shear are studied in detail.
Experimental program
- Materials and specimen fabrication
- Experimental setup and instrumentation
Dynamic response quantities such as displacement and acceleration are measured at various locations along the length of the beam. In the present study, the half-scale model is used to study the behavior of the isolated external beam-column sub-joint as shown in Figure 4.1 (a) & (b). A schematic of the reinforcement detailing at the external beam-column joint is illustrated in Figure 4.2.
A high-speed video camera (Phantom VEO 640L) was used to record the dynamic response of the beam-column subassemblies.
Numerical investigation
- Constitutive relationship for confined concrete with strain rate effect
- Constitutive material model for reinforcing steel
- Geometric and model parameters
Points (black square markers) attached along the length of the beam are used to track the transverse displacement using image correlation. Actuation of the camera is facilitated by a piezoceramic sensor (PZT) attached to the back of the beam tip, as shown in Figure 4.3. The flexural strength and ductility of the concrete section are significantly increased due to lateral confinement.
This time a variant pressure is applied over an area equal to the cross-sectional area of the shock tube.
Analytical investigation
- Moment-curvature relationship
- Resistance-deflection relationship
- Single degree of freedom (SDOF) idealization
The resisting bending moment My of the section at yield is obtained by imposing rotational equilibrium as follows:. Once the timber reinforcement has yielded, further application of the continuous moment will cause the concrete to reach its ultimate ultimate loadc,lim. At this stage, one of two scenarios is likely to occur, ie. that the pressure reinforcement is i) elastic; or ii) dividends. The total rotation at the free end is calculated using the area under the curvature diagram.
The mass factor KMis the ratio of the mass of the equivalent system ME to the total mass of the actual system M.
Results and discussion
- Experimental results
- Numerical results
- Analytical results
- Response spectra
The acceleration time histories near the beam buckling point for the specimens designed for gravity and seismic loading are shown in Figure 4.13 to Figure 4.15, respectively. For the BSNS and BSS specimens, the crack pattern at the beam-column joint is shown in Figure 4.16. The larger reinforcement spacing for the BSNS specimen resulted in severe shear cracks at the beam-column joint compared to the BFNS specimen, which can be observed in Figure 4.16 and Figure 4.17.
The peak displacement contour at the beam-column joint for the BSNS and BSS specimens is shown in Figure 4.20.
Concluding remarks
To take into account the above limitations and material uncertainties, the final resistance is reduced by a factor of 0.9 to remain on the conservative side. Since the experimental and numerical simulations are time-consuming, the estimated but conservative shock spectrum is still preferred.
Applicability of honeycomb as a sacrificial composite to resist low-
Introduction
Based on the literature review, it is found that none of the existing models are able to integrate the uncertainties related to material and geometric properties. The applicability of deterministic models often applies to a limited number of input variables. Therefore, a probabilistic model is proposed to predict the unbiased estimation of the contact force in the honeycomb sandwich structure during impact.
The accuracy of the probabilistic model depends on the availability of experimental data on a wide range of input parameters.
Experimental investigation
- Quasi-static compression test
- Dynamic impact drop test
Numerical analysis has the added advantage of providing accurate values of dimensions and material properties of the sample without uncertainty. The honeycomb core is sandwiched between rigid plates for even stress distribution during compressive loading. The peak yield stress and plateau stress of the honeycomb core were found to be 1.65 MPa (point A) and 1.08 MPa (point C), respectively.
Both the face sheets and the honeycomb core are made of an aluminum alloy Al 3003 with a yield strength of 220 MPa.
Analytical model
- Contact force formulation
- Static equivalent contact force model
The principle of minimization of potential energy is used to quantify the load displacement ratio (Timoshenko and Woinowsky-Krieger 1959). The energy balance concept is used to predict the equivalent static contact force and indentation in the sandwich panel. The kinetic energy of the impactor is balanced by strain energy induced due to bending shear, and membrane effect and work done by the contact force (Eq.(5.7)).
The global deflection (wo) and indentation( ) are estimated by solving the coupled nonlinear equations using numerical methods such as Newton-Rapson (Eq. 5.6) used to quantify the contact force due to the impact on the honeycomb structure.
Numerical simulations
The global deflection (wo) and indentation ( ) are evaluated by solving coupled nonlinear equations using numerical methods such as Newton-Rapson (Eq. 5.6), which is used to quantify the contact force due to the effect on the honeycomb structure. performing low speed impact tests on a honeycomb sandwich specimen. Once the probabilistic model is developed, it avoids any further dependence on running expensive FE simulations and predicts the contact force with an explicit equation. The thin faceplate is subjected to excessive bending and stretching of the membrane, resulting in enormous stress in the contact region.
FE simulations are performed for different material models to determine the influence on contact force and indentation.
Probabilistic contact force model
- Design of experiments
- Multiple linear regression model
- Explanatory terms and parameter estimation
- Model assessment
The probabilistic model for predicting the peak contact force on composite honeycomb structure due to low velocity impact is given as. To prove the strength of the proposed technique, the results predicted by the probabilistic model are plotted against the design of the experiment data set. The dotted lines show the bounded confidence interval of the probabilistic model of the form 1:1D.
As shown in Figure 5.10 (b), the validation points are within the confidence limits and ensure the applicability of the model.
Concluding remarks
Experimental and analytical investigation of honeycomb shielded
Introduction
However, there is limited research literature available on the performance of beam-column joints subjected to impact loading, which are most vulnerable to such threats (Birtel and Mark 2006;. Furthermore, systematic research is lacking on the protected beam-column joints using composite shielding material to withstand shock loading Reduced scale experiments are adopted to investigate the structural behavior and dynamic response of beam-column joint.
Consequence Investigations are carried out on half-scale models of external reinforced concrete beam-column joint shielded with and without honeycomb sandwich panel.
Experimental program
- Materials and specimen fabrication
The schematic representation of the reinforcement details in the external beam-column assembly is illustrated in figure 6.5. This aluminum honeycomb beam was attached to the abutment face of the beam using Z-clamp (mild steel) as shown in Figure 6.14. A schematic of the test setup and load actuator used in the current study is shown in Figure 6.6.
The discussion of the developed crack pattern at the beam-column joints is as follows.
Experimental observations
High-speed imaging of the test specimen is performed using a Phantom Model #VEO 640L high-speed camera. Camera triggering is enabled by a PZT sensor attached to the rear of the beam tip.
Experimental results and findings
- Effect of impact velocity and energy absorption characteristics
- Evaluation of target damage using crater analysis technique
- Study of target morphology after impact
- Evolution of cracks near beam-column joint
- Transient displacement response
- Acceleration time history
The comparison plots of the ballistic limit of the non-seismic group samples compared to seismic group samples for with and without honeycomb shielding are shown in Figure 6.17. The ratio between energy absorption and surface density is minimal for the samples shielded with a 50 mm thick honeycomb. The comparison graphs of the ratio between the energy absorption and the areal density of the non-seismic group specimens compared to seismic group specimens for with and without honeycomb shielding are shown in Figure 6.18.
The concrete surface was chipped for all test specimens in the non-seismic group (NS-A).
Concluding remarks
Conclusions and future scope
Conclusions
Limitations of the current dissertation
Scope of future work
