Experimental Characterization for Helmet Pads

2017 ◽  
Author(s):  
Timothy G. Zhang ◽  
Chris Meredith ◽  
Allison Muller ◽  
Paul Moy ◽  
Sikhanda S. Satapathy
Keyword(s):  
Compression Tests ◽  
Dynamic Impact ◽  
Engineering Strain ◽  
Static Compression ◽  
Static Tests ◽  
Material Stiffness ◽  
Rigid Projectile ◽  
Time Histories ◽  
The Impact ◽  
Impact Experiments

In this study, quasi-static compression and dynamic impact experiments were conducted on helmet pads. Various layers of the foam pad: comfort, stiff and bilayer were tested to characterize their material response. In the compression tests, a piston compressed foam samples at constant velocity. The samples were tested under confined and unconfined conditions. In the dynamic impact experiments, the foam samples were impacted by a rigid projectile. Both the time histories of the force applied to the foam samples and the sample displacement were recorded to calculate the engineering strain and stress in the foam samples. The material stiffness in the impact tests was found to be several times that of the quasi-static tests.

Experimental investigation of the quasi-static and impact tests on the energy absorption characteristics of coupler rubber buffers used in railway vehicles

2018 ◽  
Vol 233 (9) ◽  
pp. 937-950 ◽  
Author(s):  
Shuguang Yao ◽  
Zhixiang Li ◽  
Wen Ma ◽  
Ping Xu ◽  
Quanwei Che
Keyword(s):  
Energy Absorption ◽  
Impact Velocity ◽  
High Speed ◽  
Compression Tests ◽  
Static Compression ◽  
Static Tests ◽  
Impact Tests ◽  
High Speed Trains ◽  
The Impact ◽  
Absorption Characteristics

Coupler rubber buffers are widely used in high-speed trains, to dissipate the impact energy between vehicles. The rubber buffer consists of two groups of rubbers, which are pre-compressed and then installed into the frame body. This paper specifically focuses on the energy absorption characteristics of the rubber buffers. Firstly, quasi-static compression tests were carried out for one and three pairs of rubber sheets, and the relationship between the energy absorption responses, i.e. Eabn  =  n ×  Eab1, Edissn =  n ×  Ediss1, and Ean =  Ea1, was obtained. Next, a series of quasi-static tests were performed for one pair of rubber sheet to investigate the energy absorption performance with different compression ratios of the rubber buffers. Then, impact tests with five impact velocities were conducted, and the coupler knuckle was destroyed when the impact velocity was 10.807 km/h. The results of the impact tests showed that with the increase of the impact velocity, the Eab, Ediss, and Ea of the rear buffer increased significantly, but the three responses of the front buffer did not increase much. Finally, the results of the impact tests and quasi-static tests were contrastively analyzed, which showed that with the increase of the stroke, the values of Eab, Ediss, and Ea increased. However, the increasing rates of the impact tests were higher than that of the quasi-static tests. The maximum value of Ea was 68.76% in the impact tests, which was relatively a high value for the vehicle coupler buffer. The energy capacity of the rear buffer for dynamic loading was determined as 22.98 kJ.

Low-velocity impact behavior of flexible sandwich composite with polyurethane grid sealing shear thickening fluid core

2019 ◽  
Vol 22 (4) ◽  
pp. 1274-1291 ◽  
Author(s):  
Liwei Wu ◽  
Jing Wang ◽  
Qian Jiang ◽  
Zhenqian Lu ◽  
Wei Wang ◽  
...  
Keyword(s):  
Shear Thickening ◽  
Compression Modulus ◽  
Low Velocity Impact ◽  
Impact Behavior ◽  
Sandwich Composite ◽  
Control Group ◽  
Dynamic Impact ◽  
Low Velocity ◽  
Static Compression ◽  
The Impact

In this study, a new type of flexible sandwich composite with nonwoven facesheets and core reinforced by polyurethane (PU) grid sealing shear thickening fluid (STF) has been presented. With the specific design, the STF was sealed into PU grids as the core to provide shear thickening effect against impact. Rheological property of STF with different mass ratio and PU morphology after first and second foaming were evaluated and optimized for sandwich composite preparation. Both static compression and dynamic impact tests were carried out to obtain the impact dynamic response and investigate the effects of typical parameters including STF volume, core thickness and striker height on low-velocity impact behavior. The test results showed that the optimal concentration of STF was 20 wt.%, whose critical shear rate was 100s−1. The presence of STF had a positive influence on the static compression strength and dynamic impact strength. In particular, the 70% STF volume fraction contributed to the highest compression modulus. The compression modulus was 445 MPa and 466 MPa when the sample thickness was 2 cm and 3 cm, respectively. As for dynamic impact strength with corresponding STF volume fractions, it was 4535.31 mJ for 30%, 4599.72 mJ for 50%, and 4827.46 mJ for 70%, all of which were much higher than that (2348 mJ) of control group (without STF). Regardless of whether the STF volume being 30%, 50% and 70%, the impact displacement of composite was within 10 mm, showing better impact resistance than control group (13.16 mm). Besides, this composite with special PU grid sealing, STF structure demonstrated a certain strain rate effect. The higher the impact energy, the greater the energy absorption was. Specifically, impact energy absorption rate of composite with a thickness of 3 cm was as high as 52.3% under 350 mm impact height.

Effect of Laser Forming on the Energy Absorbing Behavior of Metal Foams

2021 ◽  
pp. 1-29
Author(s):  
Tom Zhang ◽  
Yubin Liu ◽  
Nathan Ashmore ◽  
Wayne Li ◽  
Y. Lawrence Yao
Keyword(s):  
Metal Foam ◽  
Laser Forming ◽  
Compression Tests ◽  
Forming Process ◽  
Static Compression ◽  
Closed Cell ◽  
Similarities And Differences ◽  
Energy Absorbing ◽  
The Impact ◽  
Quasi Static Compression

Abstract Metal foam is light in weight and exhibits an excellent impact absorbing capability. Laser forming has emerged as a promising process in shaping metal foam plates into desired geometry. While the feasibility and shaping mechanism has been studied, the effect of the laser forming process on the mechanical properties and the energy absorbing behavior in particular of the formed foam parts has not been well understood. This study comparatively investigated such effect on as-received and laser formed closed-cell aluminum alloy foam. In quasi-static compression tests, attention paid to the changes in the elastic region. Imperfections near the laser irradiated surface were closely examined and used to help elucidate the similarities and differences in as-received and laser formed specimens. Similarly, from the impact tests, differences in deformation and specific energy absorption were focused on, while relative density distribution and evolution of foam specimens were numerically investigated.

Dynamic and Quasi-Static Compression Tests for Polylactic Acid Resin Foam

2012 ◽  
Vol 706-709 ◽  
pp. 745-750 ◽  
Author(s):  
Hidetoshi Kobayashi ◽  
Keitaro Horikawa ◽  
Keiko Watanabe ◽  
Kinya Ogawa ◽  
Kensuke Nozaki
Keyword(s):  
Strain Rate ◽  
Polylactic Acid ◽  
High Speed ◽  
Impact Load ◽  
Video Camera ◽  
Compression Tests ◽  
Rate Dependency ◽  
Static Compression ◽  
Acid Resin ◽  
The Impact

In this study, the effect of strain rate on the strength and the absorbed energy of polylactic acid resin foam (PLA-foam), which is generally known as one of carbon-neutral and environmentally-friendly polymers, were examined by a series of compression tests at various strain rates from 0.001 to 750 s-1. For the measurements of the impact load and the displacement of specimen, a special load cell and a high-speed video camera were used, respectively. The flow stress of the PLA-foam strongly depends upon not only strain rate but also density of specimens. Thus, a new technique to eliminate the effect of the difference in the specimen density was proposed and successfully applied. It was also found that the strain-rate dependency of PLA-foam can be expressed by a simple power law.

scholarly journals Investigation and Statistical Modeling of the Mechanical Properties of Additively Manufactured Lattices

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 3962
Author(s):  
Derek G. Spear ◽  
Anthony N. Palazotto
Keyword(s):  
Mechanical Properties ◽  
Mechanical Performance ◽  
Design Parameters ◽  
Statistical Experimental Design ◽  
Lattice Structures ◽  
Compression Tests ◽  
Static Compression ◽  
Interaction Terms ◽  
Cell Densities ◽  
The Impact

This paper describes the background, test methodology, and experimental results associated with the testing and analysis of quasi-static compression testing of additively manufactured open-cell lattice structures. The study aims to examine the effect of lattice topology, cell size, cell density, and surface thickness on the mechanical properties of lattice structures. Three lattice designs were chosen, the Diamond, I-WP, and Primitive Triply Periodic Minimal Surfaces (TPMSs). Uniaxial compression tests were conducted for every combination of the three lattice designs, three cell sizes, three cell densities, and three surface thicknesses. In order to perform an efficient experiment and gain the most information possible, a four-factor statistical experimental design was planned and followed throughout testing. A full four-factor statistical model was produced, along with a reduced interactions model, separating the model by the significance of each factor and interaction terms. The impact of each factor was analyzed and interpreted from the resulting data, and then conclusions were made about the effects of the design parameters on the resultant mechanical performance.

Effect of Laser Forming on the Energy Absorbing Behavior of Metal Foams

2021 ◽  
Author(s):  
Tom Zhang ◽  
Yubin Liu ◽  
Y. Lawrence Yao
Keyword(s):  
Metal Foam ◽  
Metal Foams ◽  
Laser Forming ◽  
Test Scheme ◽  
Compression Tests ◽  
Forming Process ◽  
Band Formation ◽  
Static Compression ◽  
Energy Absorbing ◽  
The Impact

Abstract Metal foam is light in weight and exhibits an excellent impact absorbing capability. Laser forming has emerged as a promising process in shaping metal foam plates into desired geometry. While the feasibility and shaping mechanism has been studied, the effect of the laser forming process on the mechanical properties and the energy absorbing behavior in particular of the formed foam parts has not been well understood. This study comparatively investigated such effect on as-received and laser formed closed-cell aluminum alloy foam. In quasi-static compression tests, attention was paid to the changes in the elastic region. Imperfections near the laser irradiated surface were closely examined and used to help elucidate the similarities and differences in as-received and laser formed specimens. Similarly, from the impact tests, the dynamically induced deformation and crush band formation were investigated with a modified Charpy impact test scheme. Differences in specific energy absorption were studied and were related to the defects formed during laser forming process. The relative density distribution and evolution of foam specimens were numerically investigated. Laser induced imperfections lead to very minor decrease in the energy absorbing ability of the metal foam, and laser forming still remain as a viable shaping process for metal foams.

Static and Dynamic Properties of Various Baseballs

1998 ◽  
Vol 14 (4) ◽  
pp. 390-400 ◽  
Author(s):  
Shonn P. Hendee ◽  
Richard M. Greenwald ◽  
Joseph J. Crisco
Keyword(s):  
Energy Loss ◽  
Dynamic Properties ◽  
Impact Behavior ◽  
Dynamic Impact ◽  
Ball Impact ◽  
Static Compression ◽  
Stationary Target ◽  
Static Tests ◽  
Static Mechanical ◽  
Force Time

In this study we investigated the compressive quasi-static mechanical properties and dynamic impact behavior of baseballs. Our purpose was to determine if static testing could be used to describe dynamic ball impact properties, and to compare static and dynamic properties between traditional and modified baseballs. Average stiffness and energy loss from 19 ball models were calculated from quasi-static compression data. Dynamic impact variables were determined from force–time profiles of balls impacted into a flat stationary target at velocities from 13.4 to 40.2 m/s. Peak force increased linearly with increasing ball model stiffness. Impulse of impact increased linearly with ball mass. Coefficient of restitution (COR) decreased with increasing velocity in all balls tested, although the rate of decrease varied among the different ball models. Neither quasi-static energy loss nor hysteresis was useful in predicting dynamic energy loss (COR2). The results between traditional and modified balls varied widely in both static and dynamic tests, which is related to the large differences in mass and stiffness between the two groups. These results indicate that static parameters can be useful in predicting some dynamic impact variables, potentially reducing the complexity of testing. However, some variables, such as ball COR, could not be predicted with the static tests performed in this study.

scholarly journals A Research Procedure for Examining the Dynamic Properties of Multi-Wire Springs used in NR-30 Guns

2019 ◽  
Vol 10 (3) ◽  
pp. 61-78
Author(s):  
Patryk MODRZEJEWSKI ◽  
Zdzisław IDZIASZEK
Keyword(s):  
Dynamic Properties ◽  
Dynamic Compression ◽  
Compression Tests ◽  
Limit Values ◽  
Static Tests ◽  
Static Test ◽  
Research Results ◽  
Spring Force ◽  
Research Procedure ◽  
The Impact

The article presents a concept of the procedure for researching the dynamic properties of the multi-wire springs used in NR-30 guns. The aim of the research was to check the possibilities of determining the limit values of the flexibility of the multi-wire springs for the NR-30 gun, as well as to verify the obtained research results using those from range and static tests (after long compression). While verifying the method (selected measurements of 4 springs with varying degrees of wear), static and dynamic compression tests were performed on a spring mounted on a gun on specially prepared testing stations. The description of the data measurement and acquisition method applied should be considered an important element of the description of a testing station. Based on the obtained research results, it has been inferred that, during the striker’s backward movement, wave phenomena likely transpire in the spring. Force value fluctuations taking place during the spring’s movement are visible in the obtained diagrams. The dynamic and static test results (on springs with varying degrees of wear) allowed the authors to evaluate the impact of a multi-wire spring’s wear on the value of its force of interaction with the automation elements of an NR-30. Based on the data obtained, the assumptions for the method of evaluating multi-wire springs’ durability and using it to evaluate the suitability of a given spring type for use according to its technical state, have been elaborated. The final determination of the limit values of the springs’ parameters requires further research using a station with an ammunition belt encumbrance emulator, as well as emulation of the overloads of the kinematic arrangement of the gun while airborne.

scholarly journals Reactions of Al-PTFE under Impact and Quasi-Static Compression

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
Bin Feng ◽  
Xiang Fang ◽  
Yu-chun Li ◽  
Shuang-zhang Wu ◽  
Yi-ming Mao ◽  
...  
Keyword(s):  
Energy Level ◽  
Dynamic Test ◽  
Dynamic Impact ◽  
Sem Images ◽  
Static Loads ◽  
Static Compression ◽  
Static Tests ◽  
The Difference ◽  
Quasi Static Compression

Conventionally, the Al-PTFE is thought to be inert under quasi-static or static loads. However, here we reported an initiation phenomenon of Al-PTFE under quasi-static compression. Quasi-static tests suggest that reacted Al-PTFE samples had much higher toughness than unreacted samples. Dynamic test showed that the energy level needed to initiate the material was similar for quasi-static compression (88–100 J) and dynamic impact (77–91 J). The difference in density indicates that unreacted Al-PTFE has a higher crystallinity, which leads to the lower toughness. SEM images show numerous PTFE fibrils in unreacted composites which made the sample harder to crack and initiate.

scholarly journals On the relationship between force reduction, loading rate and energy absorption in athletics tracks

2017 ◽  
Vol 232 (2) ◽  
pp. 71-78 ◽  
Author(s):  
Luca Andena ◽  
Antonio Ciancio ◽  
Francesco Briatico-Vangosa ◽  
Stefano Mariani ◽  
Andrea Pavan
Keyword(s):  
Material Properties ◽  
Loading Rate ◽  
Stored Energy ◽  
Compression Tests ◽  
Static Compression ◽  
Track Geometry ◽  
Force Reduction ◽  
The Impact ◽  
The Relationship ◽  
Quasi Static Compression

In this work, finite element simulations of typical sports surfaces were performed to evaluate parameters, such as the loading rate and the energy absorbed by the surface, in relation to its characteristics (surface structure and material properties). Hence, possible relations between these quantities and the standard parameters used to characterize the shock absorbing characteristics of the athletics track (in particular, its force reduction) were investigated. The samples selected for this study were two common athletics tracks and a sheet of natural rubber. They were first characterized by quasi-static compression tests; their mechanical properties were extrapolated to the strain rate of interest and their dependence on the level of deformation was modelled with hyperelastic constitutive equations. Numerical simulations were carried out for varying sample thicknesses to understand the influence of track geometry on force reduction, loading rate and stored energy. A very good correlation was found between force reduction and the other relevant parameters, with the exception of the loading rate at the beginning of the impact.

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