scholarly journals Strain Rate Dependent Behavior of Vinyl Nitrile Helmet Foam in Compression and Combined Compression and Shear

2020 ◽  
Vol 10 (22) ◽  
pp. 8286
Author(s):  
Nicolas Bailly ◽  
Yvan Petit ◽  
Jean-Michel Desrosier ◽  
Olivier Laperriere ◽  
Simon Langlois ◽  
...  
Keyword(s):  
Strain Rate ◽  
Shear Loading ◽  
Combined Loading ◽  
Impact Behavior ◽  
Rate Variation ◽  
Shear Stresses ◽  
Absorbed Energy ◽  
Static Compression ◽  
Rate Dependent ◽  
Dependent Behavior

Vinyl nitrile foams are polymeric closed-cell foam commonly used for energy absorption in helmets. However, their impact behavior has never been described in isolation. This study aims to characterize the strain rate dependent behavior of three VN foams in compression and combined compression and shear. Vinyl nitrile samples of density 97.5, 125, and 183 kg/m3 were submitted to quasi-static compression (0.01 s−1) and impacts in compression and combined compression and shear (loading direction of 45°). For impacts, a drop test rig was used, and a method was developed to account for strain rate variation during impactor deceleration. Young’s modulus and stress at plateau were correlated with foam density in both compression and combined loading. Vinyl nitrile foams were strain rate dependent: The absorbed energy at the onset of densification was two to four times higher at 100 s−1 than at 0.01 s−1. In combined loading, the compressive stress at yield was reduced by 43% at a high strain rate. Compared to expanded polypropylene, vinyl nitrile foams transmitted less stress at the onset of densification for equivalent absorbed energy and presented a larger ratio between the compression and shear stresses in combined loading (0.37 at yield). This larger ratio between the compression and shear stresses might explain why vinyl nitrile helmet liners are thought to be better at reducing head rotational acceleration than expanded polypropylene helmet liners.

scholarly journals Characterization of Strain Rate-Dependent Behavior of 63Sn-37Pb Solder Using Split Hopkinson Torsional Bars (SHTB)

2001 ◽  
Author(s):  
Shi-Wei Ricky Lee ◽  
Lan Hong Dai
Keyword(s):  
Solder Joint ◽  
Strain Rate ◽  
Shear Loading ◽  
Rate Dependent ◽  
Dependent Behavior ◽  
Split Hopkinson ◽  
Dynamic Shear Strength ◽  
Torsion Bar ◽  
Dependent Behaviour

Abstract The present study is aimed at the experimental characterization of strain-rate dependent behaviour of solder materials under impulsive shear loading. In order to achieve this objective, a unique testing technique, namely, split Hopkinson torsion bar (SHTB) is employed. The solder material under investigation is 63Sn-37Pb. The experimental results indicate that the shear behavior of the solder joint is very sensitive to the strain rate and the dynamic shear strength of the solder joint is much higher than the static one.

Influence of strain rate, temperature and fatigue on the radial compression behaviour of Norway spruce

Holzforschung ◽  
2017 ◽  
Vol 71 (6) ◽  
pp. 505-514 ◽  
Author(s):  
Carolina Moilanen ◽  
Tomas Björkqvist ◽  
Markus Ovaska ◽  
Juha Koivisto ◽  
Amandine Miksic ◽  
...  
Keyword(s):  
Strain Rate ◽  
Linear Model ◽  
Norway Spruce ◽  
Material Model ◽  
Radial Compression ◽  
Compression Tests ◽  
Static Compression ◽  
Rate Dependent ◽  
Compression Model ◽  
Wood Compression

Abstract A dynamic elastoplastic compression model of Norway spruce for virtual computer optimization of mechanical pulping processes was developed. The empirical wood behaviour was fitted to a Voigt-Kelvin material model, which is based on quasi static compression and high strain rate compression tests (QSCT and HSRT, respectively) of wood at room temperature and at high temperature (80–100°C). The effect of wood fatigue was also included in the model. Wood compression stress-strain curves have an initial linear elastic region, a plateau region and a densification region. The latter was not reached in the HSRT. Earlywood (EW) and latewood (LW) contributions were considered separately. In the radial direction, the wood structure is layered and can well be modelled by serially loaded layers. The EW model was a two part linear model and the LW was modelled by a linear model, both with a strain rate dependent term. The model corresponds well to the measured values and this is the first compression model for EW and LW that is based on experiments under conditions close to those used in mechanical pulping.

Static and Impact Behavior of Self-Pierced Rivet Connections in Aluminum

2001 ◽  
Author(s):  
Chelliah Madasamy ◽  
Omar Faruque ◽  
Tau Tyan ◽  
Robert Thomas
Keyword(s):  
Strain Rate ◽  
Design Process ◽  
Failure Modes ◽  
Shear Loading ◽  
Peak Force ◽  
Impact Behavior ◽  
Impact Performance ◽  
Lap Shear ◽  
Shear Modes ◽  
Importance Assessment

Abstract Self-pierced riveted (SPR) connections in aluminum coupons were tested to evaluate their static and impact performance for automotive vehicle applications. The variables studied included: top gage, bottom gage, rivet size, adhesive, pre-strain, rivet location, strain-rate, and temperature. The SPR connections were tested for coach peel, u-tension, and lap shear modes. A variable importance assessment as well as the estimated effect of the variables on peak force and energy absorption was determined. The failure modes observed during testing were consistent. From this study, it was found that the top gage, bottom gage, and temperature were very sensitive for coach peel, u-tension, and lap shear. Additionally, adhesive was found to be important for shear loading, strain-rate increased the peak force when adhesive was present and, rivet size had a significant effect on both u-tension and coach peel modes. The effect of pre-strain and rivet location was minimal, and therefore their effect in the design process can be considered minimal.

scholarly journals Non-coaxiality of sand under bi-directional shear loading

2018 ◽  
Vol 5 (5) ◽  
pp. 172076 ◽  
Author(s):  
Yao Li ◽  
Yunming Yang
Keyword(s):  
Shear Stress ◽  
Strain Rate ◽  
Simple Shear ◽  
Shear Test ◽  
Shear Loading ◽  
Shear Behaviour ◽  
Shear Stresses ◽  
Simple Shear Test ◽  
Principal Axes ◽  
Angle Difference

This study aims to investigate the effect of consolidation shear stress magnitude on the shear behaviour and non-coaxiality of soils. In previous drained bi-directional simple shear test on Leighton Buzzard sand, it is showed that the level of non-coaxiality, which is indicated by the angle difference between the principal axes of stresses and the corresponding principal axes of strain rate tensors, is increased by increasing angle difference between the direction of consolidation shear stress and secondary shearing. This paper further investigated the relation and includes results with higher consolidation shear stresses. Results agree with the previous relation, and further showed that increasing consolidation shear stresses decreased the level of non-coaxiality in tests with angle difference between 0° and 90°, and increased the level of non-coaxiality in tests with angle difference between 90° and 180°.

Athermal and Thermal Limits of the Grain Refinement by SPD

2008 ◽  
Vol 584-586 ◽  
pp. 938-943 ◽  
Author(s):  
Martin Hafok ◽  
Reinhard Pippan
Keyword(s):  
Strain Rate ◽  
Grain Refinement ◽  
Single Phase ◽  
High Pressure Torsion ◽  
Bulk Materials ◽  
Microstructural Refinement ◽  
Thermal Limits ◽  
Rate Dependent ◽  
Dependent Behavior ◽  
Saturation Region

Severe plastic deformation, SPD, enables the grain refinement of bulk materials. However, at strains larger than a critical value, no further microstructural refinement can be observed. This regime is denoted as saturation region of the microstructural size. It will be shown that this regime can be divided into a thermal and an athermal part. The transition between these two regimes was examined in an Al-3wt.%Mg alloy. The single phase alloy was deformed by high pressure torsion (HPT) at various temperatures and different rotational speeds. During the HPTdeformation the flow stress was measured by a torque cell in a temperature range between -196°C (evaporation temperature of the liquid nitrogen) and 450°C. The temperature and the strain rate dependent behavior reveal a shift of the onset of the thermal activated regime towards higher temperatures by an increase of the strain rate.

STRAIN RATE–DEPENDENT BEHAVIOR OF UNCURED RUBBER: EXPERIMENTAL INVESTIGATION AND CONSTITUTIVE MODELING

2022 ◽  
Author(s):  
Sanghyeub Kim ◽  
Thomas Berger ◽  
Michael Kaliske
Keyword(s):  
Strain Rate ◽  
Evolution Equations ◽  
Cyclic Creep ◽  
Tensile Tests ◽  
Internal Variables ◽  
Creep Tests ◽  
Rate Dependent ◽  
Nonlinear Viscosity ◽  
Dependent Behavior ◽  
Building Process

ABSTRACT The strain rate dependence of uncured rubber is investigated through a series of tensile tests (monotonic, multistep relaxation, cyclic creep tests) at different strain rates. In addition, loading/unloading tests in which the strain rate is varied every cycle are carried out to observe their dependence on the deformation history. A strain rate–dependent viscoelastic–viscoplastic constitutive model is proposed with the nonlinear viscosity and process-dependent recovery properties observed in the test results. Those properties are implemented by introducing evolution equations for additional internal variables. The identified material parameters capture the experiments qualitatively well. The proposed model is also evaluated by finite element simulations of the building process of a tire, followed by the in-molding.

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