Impact Test Data Research Articles

Numerical study of the influences of pressure confinement on high-speed impact tests of dynamic material properties of concrete

Although tests of Modified Split-Hopkinson Pressure Bar (MSHPB) system with a pressure vessel filled with pressurized fluid or air give concrete material properties under multi-axial stress states, as will be demonstrated in this study, they do not lead to accurate results because the confining pressure under impact tests changes when specimen deforms. Unfortunately there is no reliable apparatus yet to perform impact tests on specimens with a controllable confining pressure. In this study, a mesoscale concrete model with consideration of randomly distributed aggregates is developed to study the strain rate effect on concrete under confining pressures. The results show that the strain rate sensitivity of concrete decreases with the increment of the confining pressure, indicating the strain rate effect of concrete under multi-axial stress states is less prominent as compared to that under uniaxial stress state. Using the uniaxial impact testing data overestimates the strain rate effect of concrete material under multi-axial stress states. An empirical relation is proposed in this study to model the concrete Dynamic Increase Factor (DIF) for the case with pressure confinement, which can be used to more accurately represent the DIF of concrete material under multi-axial stress states.

Modeling Dynamic Anisotropic Behaviour and Spall Failure in Commercial Aluminium Alloys AA7010

This paper presents a finite strain constitutive model to predict a complex elastoplastic deformation behaviour involves very high pressures and shockwaves in orthotropic materials of aluminium alloys. The previous published constitutive model is used as a reference to start the development in this work. The proposed formulation that used a new definition of Mandel stress tensor to define Hill’s yield criterion and a new shock equation of state (EOS) of the generalised orthotropic pressure is further enhanced with Grady spall failure model to closely predict shockwave propagation and spall failure in the chosen commercial aluminium alloy. This hyperelastic-plastic constitutive model is implemented as a new material model in the Lawrence Livermore National Laboratory (LLNL)-DYNA3D code of UTHM’s version, named Material Type 92 (Mat92). The implementations of a new EOS of the generalised orthotropic pressure including the spall failure are also discussed in this paper. The capability of the proposed constitutive model to capture the complex behaviour of the selected material is validated against range of Plate Impact Test data at 234, 450 and 895 ms−1 impact velocities.

An anisotropic elastoplastic constitutive formulation generalised for orthotropic materials

This paper presents a finite strain constitutive model to predict a complex elastoplastic deformation behaviour that involves very high pressures and shockwaves in orthotropic materials using an anisotropic Hill’s yield criterion by means of the evolving structural tensors. The yield surface of this hyperelastic–plastic constitutive model is aligned uniquely within the principal stress space due to the combination of Mandel stress tensor and a new generalised orthotropic pressure. The formulation is developed in the isoclinic configuration and allows for a unique treatment for elastic and plastic orthotropy. An isotropic hardening is adopted to define the evolution of plastic orthotropy. The important feature of the proposed hyperelastic–plastic constitutive model is the introduction of anisotropic effect in the Mie–Gruneisen equation of state (EOS). The formulation is further combined with Grady spall failure model to predict spall failure in the materials. The proposed constitutive model is implemented as a new material model in the Lawrence Livermore National Laboratory (LLNL)-DYNA3D code of UTHM’s version, named Material Type 92 (Mat92). The combination of the proposed stress tensor decomposition and the Mie–Gruneisen EOS requires some modifications in the code to reflect the formulation of the generalised orthotropic pressure. The validation approach is also presented in this paper for guidance purpose. The $${\varvec{\psi }}$$ tensor used to define the alignment of the adopted yield surface is first validated. This is continued with an internal validation related to elastic isotropic, elastic orthotropic and elastic–plastic orthotropic of the proposed formulation before a comparison against range of plate impact test data at 234, 450 and $${\mathrm {895\,ms}}^{\mathrm {-1}}$$ impact velocities is performed. A good agreement is obtained in each test.

A Quantum‐Inspired Genetic Algorithm‐Based Optimization Method for Mobile Impact Test Data Integration

AbstractThe traditional impact test method needs a large number of sensors deployed on the entire structure, which cannot meet the requirements of rapid bridge testing. A new mobile impact test method is proposed by sequentially testing the substructures then integrating the test data of all substructures for flexibility identification of the entire structure. The novelty of the proposed method is that the quantum‐inspired genetic algorithm (QIGA) is proposed to improve computational efficiency by transforming the scaling factor sign determination problem to an optimization problem. Experimental example of a steel–concrete composite slab and numerical example of a three‐span continuous rigid‐frame bridge are studied which successfully verify the effectiveness of the proposed method.

Prediction of low-velocity-impact ignition threshold of energetic materials by shear-band mesoscale simulations

ABSTRACTWhen energetic materials are subjected to a low-velocity impact, they can develop viscoplastic localization, also known as an adiabatic shear band (ASB), leading to unwanted ignition. In this work, the simulation of shear band formation at mesoscale resolution has been incorporated in an ignition model. The simulation results suggest that a low-velocity impact induces the formation of an ASB, leading to ignition. Good agreement was found between the ignition model predictions and available impact test data. The ability of the model to predict the ignition threshold solely on the basis of mesoscale simulations demonstrates its superiority over existing empirical models.

Multi-Scale Modeling of Composites with Surrogate and Uncertainty in Residual Velocity for High-Speed Impacts

The bullet impact onto a composite plate has been investigated both numerically and experimentally. The main purpose is to numerically identify the range of uncertainty shown in the residual velocities from the high-speed impact test data. The simulation is based on the multi-scale modeling for composites. The experimental results presented here include the tensile tests of composite specimen to identify the range of failure strains and mainly the ballistic shot test onto a laminated plate to measure the residual velocities with especial interests in the range of uncertainty. All test data have been compared with numerical predictions and the scattered test data are reasonably well captured with simulations.

Modelling Dynamic Behaviour and Spall Failure of Aluminium Alloy AA7010

A finite strain constitutive model to predict the dynamic deformation behaviour of Aluminium Alloy 7010 including shockwaves and spall failure is developed in this work. The important feature of this newly hyperelastic-plastic constitutive formulation is a new Mandel stress tensor formulated using new generalized orthotropic pressure. This tensor is combined with a shock equation of state (EOS) and Grady spall failure. The Hill’s yield criterion is adopted to characterize plastic orthotropy by means of the evolving structural tensors that is defined in the isoclinic configuration. This material model was developed and integration into elastic and plastic parts. The elastic anisotropy is taken into account through the newly stress tensor decomposition of a generalized orthotropic pressure. Plastic anisotropy is considered through yield surface and an isotropic hardening defined in a unique alignment of deviatoric plane within the stress space. To test its ability to describe shockwave propagation and spall failure, the new material model was implemented into the LLNL-DYNA3D code of UTHM’s. The capability of this newly constitutive model were compared against published experimental data of Plate Impact Test at 234m/s, 450m/s and 895m/s impact velocities. A good agreement is obtained between experimental and simulation in each test.

Lumped mass-spring model construction for crash analysis using full frontal impact test data

Lumped Mass-Spring (LMS) model is simple but very effective for the design study of vehicle crashworthiness and occupant safety. To construct the LMS model, the SISAME software and the NHTSA test data were used. Using the SISAME, the weights of mass elements and the load-paths of spring elements were optimally and directly extracted from the test data. Among the various types of spring, the segmented inelastic type of spring was effective for the vehicle crash analysis. In this study, to obtain the occupant injuries such as HIC15 and 3 ms Chest g’s, the LMS model containing the occupant model consisted of the head, chest and pelvis was developed and validated. The modeling for the chest deflection and neck injuries was not considered in this study because of the modeling difficulties and the limitation of the SISAME software. The simulation results of occupants showed good agreements with the test results. The modeling idea for the occupant was simple but very effective.

Direct shear resistance models for simulating buried RC roof slabs under airblast-induced ground shock

Direct shear is a known response mechanism in Reinforced concrete (RC) slabs subjected to blast loads that may cause their sudden and catastrophic failure. It poses a very serious hazard to facilities subjected to blast. The empirical equations defining the direct shear resistance function for RC elements were developed in the 1970s based on results from a limited number of static tests. These equations have been used for the analyses of structural response under blast and ground shock effects since the 1980s. However, the direct shear mechanism in the short-duration dynamic domain has not been sufficiently studied, and it was not clear if those models are accurate. New static and impact test data from shear specimens with three reinforcement ratios were used to derive modified direct shear resistance functions that were different from the resistance functions proposed in the 1970s. One must determine if the new resistance functions could accurately represent the behavior of RC slabs subjected to blast loads. Furthermore, one had to understand the behavioral differences in the numerical simulations that could be associated with the two types of resistance functions, and provide recommendations on how to most appropriately represent direct shear in such analyses. This paper is focused on the assessment of the new direct shear resistance functions in RC, and the results from the parametric study were compared results obtained with the previous empirical direct shear model and with precision field test data to provide conclusions and recommendations.

Simulation study on gender differences in occupant dynamic response during spacecraft landing impact

ABSTRACTIn order to demonstrate the influence of gender differences on occupant dynamic response during spacecraft high-level landing impact, this study established a seat-dummy system model using Pro-E and HyperWorks software. The 50th Hybrid III male dummy and the 5th Hybrid III female dummy were used in the model. The seat-dummy system model was calibrated and validated according to the actual impact condition and impact test data of the simulated spacecraft landing. The gender differences on the impact response of key body segments were demonstrated and analysed under high-level landing impact (at a peak value of 26g). The simulation results show that the peak acceleration value of the female is larger than the male by 43.7% on the shoulder and by about 33% on the chest and pelvis, while the female is smaller than the male by 40.0% on the head in the chest-back (anterior–posterior, Gx) direction. In the head-foot (superior–inferior, Gz) direction, the peak acceleration value of the female is larger than the male by about 45.2% on the head, 120% on the shoulder, 9.0% on the chest and 37.3% on the pelvis. Therefore, it is recommended that spacecraft designers should pay more attention to gender differences on the head-neck and pelvis, and provide better protection for females during landing impact.

Efficient Identification of Naval High-Speed Craft Shock Mitigation Seat Modal Parameters From Drop-Test Data

Naval high-speed craft (HSC) operating in moderate to high seas experiences high-g and repeated shock loading at the seat–deck interface. These conditions are known to pose a serious potential for injury to the occupants. While various shock-mitigating seats are commercially available; their designs are in many cases quite different, and quantifying their shock attenuation characteristics can be challenging. The need for a standard test platform and experimental analysis methodology to investigate HSC seat effectiveness is a major objective of research being conducted by Carleton University's Applied Dynamics Laboratory (ADL) in partnership with Defence Research and Development Canada-Atlantic (DRDC Atlantic). A drop tower was designed and manufactured for testing HSC seats in order to characterize their shock-mitigating effectiveness by simulating the severe conditions of a slam impact at sea. Further, in order to identify seat dynamic parameters from drop-test data, the eigensystem realization algorithm (ERA), a modal-analysis-based system identification method, was applied to efficiently extract the modal parameters. The technique was shown to successfully extract the damping ratio as well as the damped and undamped natural frequencies of the seats from impact test data. The evaluated dynamic properties of the seats can subsequently inform decisions related to the design and/or procurement of commercially available seats.

Implementation of Finite Strain-Based Constitutive Formulation in LLLNL-DYNA3D to Predict Shockwave Propagation in Commercial Aluminum Alloys AA7010

The constitutive models adopted to represent dynamic plastic behaviour are of great importance in the current design and analysis of forming processes. Many have studied this topic, leading to results in various technologies involving analytical, experimental and computational methods. Despite of this current status, it is generally agreed that there is still a need for improved constitutive models. There are still many issues relating to algorithm implementation of the proposed constitutive model in the selected code to represent the proposed formulation. Using this motivation, the implementation of a new constitutive model into the LLNL-DYNA3D code to predict the deformation behaviour of commercial aluminium alloys is discussed concisely in this paper. The paper initially explains the background and the basic structure of the LLNL-DYNA3D code. This is followed by a discussion on the constitutive models that have been chosen as the starting point for this work. The initial stage of this implementation work is then discussed in order to allow all the required material data and the deformation gradient tensor F to be read and initialised for the main analysis. Later, the key section of this implementation is discussed, which mainly relates to subroutine f3dm93 including equation of state (EOS) implementation. The implementation of the elastic-plastic part with isotropic plastic hardening, which establishes the relationship between stress and strain with respect to the isoclinic configuration Ω̄i in the new deviatoric plane, is then presented before the implemented algorithm is validated against Plate Impact test data of the Aluminium Alloy 7010. A good agreement is obtained in each test.

A simple intrinsic measure for rapid crack propagation in bimodal polyethylene pipe grades validated by elastic–plastic fracture mechanics analysis of data from instrumented Charpy impact test

Conventional test procedures, such as the S4 test to analyze the resistance against rapid crack propagation (RCP) of plastic pipe materials are characterized by usage of a lot of material, are far from saving of time and they are‐in need of special experimental set‐ups. Therefore, in the last decade, small‐scale accelerated reliable tests (SMART) are developed ‐ worldwide to overcome the disadvantage of such conventional tests. In this article, fracture mechanics based analysis of instrumented Charpy impact test data for a set of bimodal high‐density polyethylene pipe grades are compared with data of the conventional Charpy impact test. From this comparison the Charpy impact strength at −30°C comes forth as a robust reproducible measure of the resistance to RCP and it is therefore proposed as a SMART method to rank materials with respect to RCP resistance. POLYM. ENG. SCI., 57:13–21, 2017. © 2016 Society of Plastics Engineers

A comparison of finite element analysis to smooth particle hydrodynamics for application to projectile impact on cementitious material

The response of structural components of high-strength cementitious (HSC) materials to projectile impact is characterized by high-rate fragmentation resulting from strong compressive shock waves coupled with reflected tensile waves. Accurate modeling of armor panels of such brittle materials under high-velocity projectile impact is a complex problem requiring meticulous experimental characterization of material properties. In a recent paper by the authors, an approach to handle such problems based on a modified Advanced Fundamental Concrete (AFC) constitutive model was developed. In the HSC panels considered in this study, an analogous approach is applied, and the predictions are verified with ballistic impact test data. Traditional Lagrangian finite element analysis (FEA) of these problems tends to introduce errors and suffers from convergence issues resulting from large deformations at free surfaces. Also, FEA cannot properly account for the issues of secondary impact of spalled fragments when multiple armor panels are used. Smoothed particle hydrodynamics (SPH) is considered to be an attractive alternative to resolve these and other issues. However, SPH-based quantitative results have been found to be less accurate than the FEA-based ones when the deformations are not sufficiently large. This paper primarily focuses on a comparison of FEA and SPH models to predict high-velocity projectile impact on single and stacked HSC panels. Results are compared to recent ballistic experiments performed as a part of this research, and conclusions are drawn based on the findings.

Estimation of fracture toughness KIC from Charpy impact test data in T-welded connections repaired by grinding and wet welding

This work presents, for the first time, and estimation of fracture toughness KIC correlations from Charpy V-notch (CVN) impact test data extracted from T-welded connections repaired with rectangular grinding and filled by wet welding. To obtain KIC values, equations based on the yield stress (σYS) of the wet welding beads were used. The estimated KIC data decreased with increasing water depth. These two characteristics (porosity and microstructures for low carbon steels) did not improve the mechanical properties, such as Charpy impact and KIC values.

Impact dynamics and puncture failure of pressurized tank cars with fluid–structure interaction: A multiphase modeling approach

This paper presents a computational framework that analyzes the effect of fluid–structure interaction (FSI) on the impact dynamics and puncture failure of pressurized commodity tank cars carrying hazardous materials. Shell (side) impact tests have been conducted on full scale tank cars resulting in deformed or punctured tank cars. A finite element (FE) modeling method is applied that explicitly simulates the three distinct phases in a tank car loaded with a liquefied substance: pressurized gas, pressurized liquid and solid structure. Furthermore, an equivalent plastic strain based fracture initiation criterion expressed as a function of stress triaxiality is adopted to depict the fracture behavior of the tank car steel material. The fracture initiation is implemented for ductile, shear and mixed fracture modes and followed by further material deterioration governed by a strain softening law. The force, displacement and impact energy results obtained from the FE analysis show good agreement with the corresponding shell impact test data. The simulations demonstrate that FSI plays a critical role in predicting the correct dynamics of tank car impact. The puncture resistance of a tank car, characterized as limit impact conditions in terms of puncture energy or puncture velocity, is further analyzed in shell impact scenarios. The puncture energy is shown to increase as the initial fluid pressure decreases, the tank car thickness increases or the effective impactor size increases. Quantitative correlations between puncture energy/velocity and each of these factors are obtained using the FE analysis method developed in this paper.

Towards optimisation of load-time conditions for producing viscoelastically prestressed polymeric matrix composites

A viscoelastically prestressed polymeric matrix composite (VPPMC) is produced by applying a tensile creep load to polymeric fibres, the load being released before the fibres are moulded into a polymeric matrix. The viscoelastically recovering fibres induce compressive stresses within the matrix, which can improve mechanical properties by up to 50%. This study investigates the feasibility of reducing the creep loading period for VPPMC production. By using nylon 6,6 fibres, we have demonstrated that the previously adopted viscoelastic creep strain, requiring 330 MPa for 24 h, can be achieved over a shorter duration, tn, using increased creep stress. Thus tn was 92 min at 460 MPa and 37 min at 590 MPa. Subject to avoiding fibre damage however, it may be possible to reduce tn further. From the three creep settings, elapsed recovery strain values were similar, as were the Charpy impact test data from corresponding VPPMC samples; i.e. there were no significant differences in impact energy absorption, these being ∼56% greater than their control (unstressed) counterparts.

Impact sensitivities of energetic materials: Exploring the limitations of a model based only on structural formulas

Using a comprehensive set of drop weight impact test data (h50) newly compiled from literature for 308 materials, a recent approach to predict impact sensitivities of nitro compounds is generalized to most explosive substances of interest. Compared to previous ones, this procedure is more thoroughly validated and exhibits a good predictive value. Furthermore, it yields new insight into the physical mechanisms involved, explaining for instance the unexpected desensitization of some oxygen-deficient triazoles upon nitration.

Comparison of stress concentrator fabrication for 3D printed polymeric izod impact test specimens

Izod impact test specimens were fabricated via a desktop grade material extrusion 3D printer process using ABS in four build orientations. The 3D printed impact test specimens were examined in order to compare the effect of stress concentrator fabrication on impact test data where two methods were used to fabricate the stress concentrating notch: (1) printing the stress concentrator; and (2) machining the stress concentrator where the dimensions of the notch matched those specified in the ASTM standard D256-10. In both test cases, sensitivity to build orientation was also observed. The sample sets with printed stress concentrators were found to be statistically similar to their counterparts with milled stress concentrators. The experiment was repeated again on a commercial grade material extrusion 3D printer using ABS, PC, PC-ABS, and Ultem 9085 and differences in impact test results were observed most notably when Ultem 9085 was tested. Scanning electron microscopy was utilized to perform fractograpy on impact test specimens to explore the effect of stress concentrator fabrication on the fracture surface morphology of the failed specimens. The work here demonstrates the need for materials testing standards that are specific to additive manufacturing technologies; as well as concluding that all-printed impact test specimens may offer the best representation of the impact characteristics of 3D printed structures.

Structural identification of short/middle span bridges by rapid impact testing: theory and verification

A structural strain flexibility identification method by processing the multiple-reference impact testing data is proposed. First, a kind of novel long-gauge fiber optic sensor is developed for structural macro-strain monitoring. Second, the multiple-reference impact testing technology is employed, during which both the impacting force and structural strain responses are measured. The impact testing technology has unique merit because it is able to extract exact structural frequency response functions (FRFs), while other test methods, for instance ambient tests, can only output the FRFs with scaled magnitudes. Most importantly, the originality of the article is that a method of identifying the structural strain flexibility characteristic from the impact test data has been proposed, which is useful for structural static strain prediction and capacity evaluation. Examples of a six meter simple supported beam and a multiple-span continuous beam bridge have successfully verified the effectiveness of the proposed method.