A Method for Assessing the Overall Impact Performance of Riot Helmets

2003 ◽  
Vol 19 (3) ◽  
pp. 246-254 ◽  
Author(s):  
Jean-Philippe Dionne ◽  
Ismail El Maach ◽  
Ahmed Shalabi ◽  
Aris Makris
Keyword(s):  
Comparative Study ◽  
Impact Energy ◽  
Energy Levels ◽  
Performance Impact ◽  
Impact Performance ◽  
Frontal Impacts ◽  
National Institute Of Justice ◽  
Crowd Control ◽  
The Face ◽  
The Impact

The objective of the present paper is to investigate the overall impact performance of various riot helmets in a comparative study. The National Institute of Justice (NIJ-0104.02) and the Canadian Standards Association (CSA-Z611-02) standards regulate the use of riot helmets in North America. Both sets of standards have a number of requirements for impact performance. Impact tests carried out with the use of a drop tower apparatus compliant with NIJ test protocols demonstrated large differences in impact attenuation level among the helmets from six manufacturers in terms of frontal and lateral impacts to the shell, and face-shield deflection. For instance, the impact energy yielding a head form acceleration of 300 g’s was measured for each helmet for frontal impacts on the helmet shell. Values ranging from 69 J up to 171 J were obtained. The energy levels of typical crowd-control threats, e.g., baton blows and projectiles, were quantified and compared with the impact energy values used in the standards. It is observed that the NIJ face-shield deflection requirement is low as compared to actual riot threats, whereas the CSA requirements are more in line with these threats. A novel method was devised to objectively assign a global impact performance score to each helmet. This method takes into account the frontal and lateral impacts to the shell as well as the face-shield deflection tests. It is based on the directional origin of the threat and the geometry of the helmets (frontal percentage area of the visor). From these global performance scores, it is possible to obtain a ranking of the various riot helmets used in the present comparative study. Based on the analysis of the global scores, it was found that appropriate protection of the face (through an impact resistant visor) is the key feature for a helmet that will be used in riot environments.

Impact Damage Detection in GFRP Laminates through Ultrasonic Imaging

2012 ◽  
Vol 585 ◽  
pp. 337-341 ◽  
Author(s):  
H. Rama Murthy Naik ◽  
J. Jerald ◽  
N. Rajesh Mathivanan
Keyword(s):  
Impact Energy ◽  
Ultrasonic Testing ◽  
Energy Levels ◽  
Low Velocity Impact ◽  
Image Processing Technique ◽  
Sound Waves ◽  
Low Velocity ◽  
Immersion Method ◽  
Pulse Echo ◽  
The Impact

Composite materials are increasingly used in aerospace, naval and automotive vehicles due to their high specific strength and stiffness. In the area of Non destructive testing, ultrasonic C-scans are used frequently to detect defects in composite components caused during fabrication and damage resulting from service conditions. Ultrasonic testing uses transmission of high frequency sound waves into a material to detect imperfections or to locate changes in material properties. The most commonly used ultrasonic testing technique is pulse echo and through transmission wherein sound is introduced into a test object and reflections (echoes) are returned to a receiver from internal imperfections. Under low-velocity impact loading delaminating is observed to be a major failure mode. This report presents the use of above two techniques to detect the damage in glass fiber reinforced plastic (GFRP) laminates. Pulse echo is used to locate the exact position of damage and through transmission is used to know the magnitude of damage in composite. This paper work will be carried out on two different thicknesses and at impact energy levels varying from 7 to 53J. The ensuring delamination damage will be determined by ultrasonic C-scans using the pulse-echo immersion method for through transmission. Delamination areas were quantified accurately by processing the raw image data using a digital image processing technique. Based on the data obtained, correlation will be established between the delamination area and the impact energy.

Control of Large-Scale Impacts by Designed Structural Damping

2005 ◽  
Author(s):  
Jan Wigaard ◽  
Christopher Hoen ◽  
Sverre Haver
Keyword(s):  
Impact Energy ◽  
Large Scale ◽  
Permanent Deformation ◽  
Energy Levels ◽  
Attractive Alternative ◽  
Safety Level ◽  
Shock Absorbers ◽  
Impact Forces ◽  
Multi Body ◽  
The Impact

Modification of deep-water floaters often involves module installation using a floating crane vessel. The impact forces caused by relative motions between the floating vessels represent a major challenge during set down on the floater deck due to the large inherent variability of these forces. Traditionally the difficulties in predicting impact forces during module installation have been overcome by the use of experienced based rules of thumb rather than accurate simulations and calculations. One has to some degree relied on the indeed present but un-quantifiable effect of human intelligence of the operation supervisor. Traditionally the impact forces are taken either by elastic deformation of the module itself and/or the installation guides or by permanent deformation of intermediate structural elements through e.g. plastic yielding of ductile metal members or crushing of wood members. Designing the module and the guides to be able to take the entire probable range of impact forces is difficult due to the inherent contradiction between wanted flexibility and required strength. The large uncertainties of the impact energy imply that it is difficult to design these intermediate elements to cover all possible impact energy levels. Furthermore, these elements cannot be applied in cases where repeated impacts may occur. An attractive alternative to the traditional solutions is application of industrial shock absorbers. The performance of these is predictable and they can be designed to cover the estimated range of impact energy. This paper will present a more precise and consistent design and analyses methodology that gives a more accurate measure on the reliability of the operation in accordance with code requirements. The paper will show application of industrial shock absorbers as an alternative to traditional solutions for impact handling during offshore module installation to floating vessels, illustrated with experience gained by the installation of two modules on the Visund Semi. Results from multi-body simulations and model tests comparing traditional methods with the proposed solution will be given. The significant benefits obtained with respect to increased operational performance, reduced acceleration loads on the installed equipment, the increased predictability of the operation, and the consistent safety level in accordance with code requirements, will be highlighted. The possibility to apply designed damping for other offshore applications like dropped object protection etc, is also discussed.

Comparative Study of Motorcycle Helmets Impact Performance

2014 ◽  
Vol 575 ◽  
pp. 306-310
Author(s):  
Hamzah Azhar ◽  
Aqbal Hafeez Ariffin ◽  
Solah Mohd Syazwan ◽  
Mohd Hafzi Md Isa ◽  
Yahaya Ahmad ◽  
...  
Keyword(s):  
Comparative Study ◽  
Impact Energy ◽  
Drop Test ◽  
Test Machine ◽  
Impact Speed ◽  
Impact Performance ◽  
Energy Absorbing ◽  
Motorcycle Helmets ◽  
Service Duration

Two sets of new and in-service helmets were impact tested using a drop test machine, in accordance to established helmet test protocols. The first test for full helmets was executed in compliance with standard speed requirements of 5.9 m/s in which three of five new helmets performed poorly. The second set utilized lower impact speed of 4 m/s for individual helmet components test. New helmet liners absorbed 5 times more impact energy than the in-service liners while the new shell was 19.3% better in dispersing impact energy than the in-service shell. The undesirable changes in liner thickness have explicit effect on the liner density which is translated into reduction in energy absorbing potential. In brief, exposure to weathering stresses and use intensities has affected helmet impact performance, regardless of service duration.

Experimental Research on the Impact Damage of Composite Laminates at Different Energies

2014 ◽  
Vol 887-888 ◽  
pp. 850-853
Author(s):  
A Ying Zhang ◽  
Han Xiong Lv ◽  
Ye Zhang ◽  
Dong Xing Zhang
Keyword(s):  
Crack Length ◽  
Experimental Research ◽  
Impact Energy ◽  
Composite Laminates ◽  
Impact Damage ◽  
Energy Levels ◽  
Cfrp Laminates ◽  
The Matrix ◽  
Impact Area ◽  
The Impact

The effects of the impact energy on the impact damage of CFRP laminates were studied in this paper. Impact tests for the CFRP laminates with the size of 600 mm×700 mm were subjected to different the impact energy levels from 5 J to 50 J. The matrix length was investigated according to different energy levels. The experimental results reveal that the crack length increases linearly with the increasing impact energy. The impact damage of CFRP laminates tends to be more severe as impact energy increases, and the impact area and crater depth increases with increasing impact energy. The surface of impact dent of specimen looks like W shape.

Impact Performance of ZnAl27Cu2.5MgMn Alloy from Room Temperature to 250°C

2014 ◽  
Vol 915-916 ◽  
pp. 597-601
Author(s):  
Ming Long Kang ◽  
Wu Hu ◽  
Jian Min Zeng
Keyword(s):  
Impact Toughness ◽  
Impact Energy ◽  
Room Temperature ◽  
Impact Testing ◽  
Impact Behavior ◽  
Impact Performance ◽  
Temperature Impact ◽  
Spectrum Curve ◽  
The Impact ◽  
Pendulum Impact

The impact performance of ZnAl27Cu2.5MgMn alloy from room Temperature to 2500 °C has been investigated by pendulum impact testing. The surface morphology of impact fracture is observed by scan electron microscope (SEM). The results indicate that impact energy of the alloy decreases as the temperature increases when the temperatures are lower than 100°C. Between 100°C and 200°C, impact energy increases as the temperature increases. And when the temperature exceeds 250°C, impact energy decreases dramatically. Impact energy gets to the maximum at room temperature. Impact behavior of the alloy can be evaluated by the width of impact spectrum curve. The wider the peak of impact spectrum curve, the higher the impact toughness. Whereas impact toughness is worse if peak is narrow.

Numerical Modelling of Impact Behavior of Composite Sandwich Panel With Honeycomb Core

2019 ◽  
Author(s):  
Shah Alam ◽  
Aakash Bungatavula
Keyword(s):  
Sandwich Panel ◽  
Sheet Thickness ◽  
Face Sheet ◽  
Honeycomb Core ◽  
Impact Performance ◽  
Composite Sandwich ◽  
The Core ◽  
The Face ◽  
Core Height ◽  
The Impact

Abstract The goal of this paper is to find the best impact response of the composite sandwich panels with honeycomb core. The focus of the study is to find the effects of changing the face sheet thickness and the core height of the sandwich panel subjected to variable velocities on impact performance. Initially, honeycomb core sandwich panel with 1mm thick face sheet is modelled in Abaqus/explicit to calculate the energy absorption, residual velocity, and deformation at four different velocities. Then, the process is repeated by changing the face sheets thickness to 2mm and 3mm to see the effects of changing the thickness on the impact performance of a composite sandwich panel. The honeycomb core height is also changed to see its effect on the performance. In all models, Al 7039 is used in the core and T1000G is used in the face sheets.

scholarly journals Experimental and numerical study of the response to various impact energy levels for composite sandwich plates with different face thicknesses

2019 ◽  
Vol 21 (5) ◽  
pp. 1654-1682
Author(s):  
Moeen S Rajput ◽  
Magnus Burman ◽  
Fredrik Forsberg ◽  
Stefan Hallström
Keyword(s):  
Impact Energy ◽  
Impact Damage ◽  
Energy Levels ◽  
Impact Response ◽  
Low Velocity Impact ◽  
Absorbed Energy ◽  
Low Velocity ◽  
Composite Sandwich ◽  
The Impact ◽  
Dent Depth

Composite sandwich structures find wide application in the aerospace sector thanks to their lightweight characteristics. However, composite structures are highly susceptible to low-velocity impact damage and therefore thorough characterization of the impact response and damage process for the used material configurations is necessary. The present study investigates the effect of face-sheet thickness on the impact response and damage mechanisms, experimentally and numerically. A uni-directional, non-crimp fabric is used as reinforcement in the face-sheets, and a closed cell Rohacell 200 Hero polymer foam is used as core material. Low-velocity impact tests are performed in a novel instrumented drop-weight rig that is able to capture the true impact response. A range of impact energies are initially utilized in order to identify when low level damage (LLD), barely visible impact damage (BVID) and visible impact damage (VID) occur. A thorough fractography investigation is performed to characterize the impact damage using both destructive and non-destructive testing. The damage from the impacts in terms of dent depth, peak contact force, deflection and absorbed energy is measured. The results show bilinear responses in dent depth vs. impact energy and absorbed energy vs. impact energy. It is found than the BVID energy works well as an indication for the onset of excessive damage. Fractography reveals that there is a failure mode shift between the LLD and the VID energy levels, and that delaminations predominantly grow along the fiber direction and rotate in a spiral pattern through the thickness, following the laminate ply orientations. Finally, a progressive damage finite element model is developed to simulate both the impact response and the delamination extent, incorporating both intra-laminar and inter-laminar damage modes. The simulation shows good agreement with the experiments.

Experimental Research on CFRP Laminates with Different Impact Energy Levels

2014 ◽  
Vol 1030-1032 ◽  
pp. 1060-1063
Author(s):  
A Ying Zhang ◽  
Dong Xing Zhang
Keyword(s):  
Crack Length ◽  
Impact Energy ◽  
Impact Damage ◽  
Energy Levels ◽  
Three Dimensional ◽  
Fatigue Loading ◽  
Crater Depth ◽  
Cfrp Laminates ◽  
65 J ◽  
The Impact

The effects of thickness and impact energy on the impact damage of CFRP laminates were studied in this paper. Impact tests for the CFRP laminates with the size of 600 mm×700 mm with five different thicknesses were subjected to impact fatigue loading at different energy levels from 5 J to 65 J. The crater depth and matrix length were investigated according to different energy levels and different thicknesses. The impact damage was evaluated by visual inspection, three-dimensional microscope. The experimental results reveal that the crater depth and the crack length increase with the increasing impact energy. For the same impact energy, the crater depth and the crack length decreased with the increasing thickness of specimens.

The flexural behaviors of the impacted composite single-lap adhesive joints

2015 ◽  
Vol 22 (5) ◽  
Author(s):  
Emin Ergun ◽  
Hasan Çallioğlu
Keyword(s):  
Experimental Study ◽  
Impact Energy ◽  
Energy Levels ◽  
Composite Plates ◽  
Lap Joints ◽  
Adhesive Joints ◽  
Single Lap Joints ◽  
Impact Tests ◽  
Impact Energies ◽  
The Impact

AbstractThis experimental study deals with the flexural behaviors of composite single-lap adhesive joints after impact tests. Increasing impact energies are applied at the center of the composite plates having three different overlap lengths. It is shown that the overlap lengths and impact energy levels affect considerably the impact responses of the composite single-lap joints. It is also shown that the bending stiffness of the composite increases with increasing overlap length. For this reason, after the impact tests, how these effects influence the flexural behaviors of the impacted composite lap joints was also investigated. The flexural loads of the impacted and non-impacted composite single-lap joints were determined and compared with each other. It is shown that the residual flexural loads after impact increase with increasing overlap lengths but decrease with increasing impact energy.

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