Dynamic Stress-Strain Measurements By High Speed Streak Photography

1989 ◽  
Author(s):  
Lippe D. Sadwin
Keyword(s):  
High Speed ◽  
Dynamic Stress ◽  
Stress Strain ◽  
Strain Measurements

One-Dimensional Dynamic Compressive Behavior of EPDM Rubber

2003 ◽  
Vol 125 (3) ◽  
pp. 294-301 ◽  
Author(s):  
B. Song ◽  
W. Chen
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Dynamic Stress ◽  
Split Hopkinson Pressure Bar ◽  
Constant Strain Rate ◽  
Strain Rates ◽  
Hopkinson Pressure Bar ◽  
Stress Strain ◽  
Epdm Rubber ◽  
One Dimensional

Dynamic compressive stress-strain curves at various strain rates of an Ethylene-Propylene-Diene Monomer Copolymer (EPDM) rubber have been determined with a modified split Hopkinson pressure bar (SHPB). The use of a pulse-shaping technique ensures that the specimen deforms at a nearly constant strain rate under dynamically equilibrated stress. The validity of the experiments was monitored by a high-speed digital camera for specimen edge deformation, and by piezoelectric force transducers for dynamic stress equilibrium. The resulting dynamic stress-strain curves for the EPDM indicate that the material is sensitive to strain rates and that the strain-rate sensitivity depends on the value of strain. Based on a strain energy function theory, a one-dimensional dynamic constitutive equation for this rubber was modified to describe the high strain-rate experimental results within the ranges of strain and strain rates presented in this paper.

Dynamic Viscoelastic Properties of Raw Butadiene—Acrylonitrile Elastomers

1974 ◽  
Vol 47 (4) ◽  
pp. 778-787 ◽  
Author(s):  
N. Nakajima ◽  
E. A. Collins ◽  
P. R. Kumler
Keyword(s):  
Shear Stress ◽  
Tensile Stress ◽  
Viscoelastic Properties ◽  
High Speed ◽  
Master Curve ◽  
Viscoelastic Behavior ◽  
Master Curves ◽  
Stress Strain ◽  
Strain Measurements ◽  
Using Data

Abstract The dynamic viscoelastic properties of four samples of butadiene—acrylonitrile raw elastomers, were obtained with a Rheovibron at 110 Hz and temperature range of −80 to 160°C. The complex properties were in agreement with the master curves obtained previously from stress-strain measurements. A master curve encompassing 13 decades of time was constructed using data from Mooney rheometer shear stress-strain, MTS high speed tensile stress-strain, and the Rheovibron. The master curve represents the rubbery region of viscoelastic behavior in terms of time, temperature, and the magnitude of deformation up to the breaking point. This study demonstrates that corresponding states can be found between small (ca. 1 per cent) and large deformation up to break (e.g., 1400 per cent).

Dynamic Behavior Characterization of Lead at High Strain Rates Using High Speed Photography for Finite Element Simulation

2005 ◽  
Author(s):  
G. S. Sohoni ◽  
M. V. Walame ◽  
V. Tandon ◽  
R. S. Mahajan ◽  
S. Raju
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Dynamic Stress ◽  
High Strain ◽  
Computational Techniques ◽  
High Speed Photography ◽  
Radial Deformation ◽  
Strain Rates ◽  
High Strain Rates ◽  
Stress Strain

This paper reviews experimental as well as computational techniques for determining stress-strain characteristics of materials at high strain rates. Quasi-static and dynamic compression tests were performed on standard Lead (Pb) specimens of three different L/D ratios, 0.8, 2 and 3. A Drop tower system was used to achieve different strain rates along with high-speed camera to capture the vertical and radial deformation of specimen and accelerometers to capture load data. The results obtained from the experiments were processed to generate dynamic stress-strain curve for Lead under different strain rate conditions. It was observed that the dynamic stress increases with increasing strain rate. The information gained is valuable for validating constitutive models.

scholarly journals Numerical analysis of local strain measurements in fluid-saturated rock samples submitted to forced oscillations

Geophysics ◽  
2018 ◽  
Vol 83 (5) ◽  
pp. MR309-MR316 ◽  
Author(s):  
Samuel Chapman ◽  
Beatriz Quintal
Keyword(s):  
Dynamic Stress ◽  
Forced Oscillation ◽  
Local Strain ◽  
Strain Response ◽  
Stress Strain ◽  
Strain Measurements ◽  
Rock Samples ◽  
Bulk Strain ◽  
Saturated Sample ◽  
Water Saturated

The forced oscillation method is used to experimentally study the viscoelastic behavior of fluid-saturated rocks at seismic frequencies by measuring their dynamic stress-strain response. The strain on a sample can be measured locally with strain gauges or on the entire sample, here referred to as bulk strain, with a displacement transducer. The local response can vary greatly from the bulk because of heterogeneities in the rock, which can be structural in nature, for example, fractures, or they can arise from partial fluid saturation. Comparing the results from experimental setups that measure strains by different methods can therefore become problematic, and setups that exclusively measure local strains can be inadequate for performing certain experiments. To better understand these limitations, we numerically simulate forced oscillation tests on models representative of laboratory samples, using Biot’s quasistatic equations for poroelastic media. The main objective is to analyze the discrepancies that can arise between local and bulk measurements, with a specific focus on the frequency-dependent attenuation and the Young’s modulus dispersion. We find that, for a fully water-saturated sample having a single fracture and for a partially saturated sample, the local responses deviate significantly from the bulk responses. In addition, the average of three local measurements along a sample allows for approximating the bulk response for the case of a partially water-saturated sample having a homogeneous solid frame. Such an average is not sufficient for the fractured sample. In summary, the averaging of local strain measurements can provide a partial solution to accurately characterize the dynamic stress-strain response of the sample in certain cases, but in other cases, it can lead to results that strongly deviate from the bulk measurements. We advocate for experimental setups to be built to measure the bulk strain on rock samples or modified to include this measurement in addition to local ones.

A Master Curve for Amorphous Elastomers Derived from Small and Large Deformations Using Various Instruments

1975 ◽  
Vol 48 (1) ◽  
pp. 69-78 ◽  
Author(s):  
N. Nakajima ◽  
E. A. Collins
Keyword(s):  
Steady State ◽  
Viscoelastic Properties ◽  
High Speed ◽  
Master Curve ◽  
Large Deformations ◽  
Stress Strain ◽  
Strain Measurements ◽  
Mechanical Measurements ◽  
Single Master Curve ◽  
Butadiene Styrene

Abstract Dynamic mechanical measurements, stress—strain measurements, and steady-shear measurements made over a range of temperatures and frequencies or deformation rates are used to characterize the viscoelastic properties of raw elastomers. The measurements involve both small and large deformations. It is shown that the results on either butadiene—acrylonitrile (NBR) or butadiene—styrene (SBR) can be reduced to a single master curve. The instruments and ranges covered included Instron stress—strain (0.2–20 in./min; 25–75°C), Instron capillary (100−104sec −1; 100°C), Rheovibron (110 Hz; 23–156°C), Rheometrics (4×10−2−2.6×102 sec−1; 100°C), MTS high speed tester (267-26 700%/sec; 25–97°C), steady-state Mooney (0.05–20 rpm; 25–150°C) and transient Mooney (0.05 rpm; 25–150°C).

scholarly journals An Improved Lagrangian-Inverse Method for Evaluating the Dynamic Constitutive Parameters of Concrete

Materials ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 1871
Author(s):  
Xinlu Yu ◽  
Yingqian Fu ◽  
Xinlong Dong ◽  
Fenghua Zhou ◽  
Jianguo Ning
Keyword(s):  
High Speed ◽  
Inverse Method ◽  
Image Correlation ◽  
Analysis Method ◽  
Stress Strain ◽  
Optical Techniques ◽  
Element Simulation ◽  
Non Linear ◽  
Constitutive Parameters ◽  
Inverse Analysis Method

The dynamic constitutive behaviors of concrete-like materials are of vital importance for structure designing under impact loading conditions. This study proposes a new method to evaluate the constitutive behaviors of ordinary concrete at high strain rates. The proposed method combines the Lagrangian-inverse analysis method with optical techniques (ultra-high-speed camera and digital image correlation techniques). The proposed method is validated against finite-element simulation. Spalling tests were conducted on concretes where optical techniques were employed to obtain the high-frequency spatial and temporal displacement data. We then obtained stress–strain curves of concrete by applying the proposed method on the results of spalling tests. The results show non-linear constitutive behaviors in these stress–strain curves. These non-linear constitutive behaviors can be possibly explained by local heterogeneity of concrete. The proposed method provides an alternative mean to access the dynamic constitutive behaviors which can help future structure designing of concrete-like materials.

Measurement of Dynamic Strain

1943 ◽  
Vol 10 (2) ◽  
pp. A85-A92
Author(s):  
C. O. Dohrenwend ◽  
W. R. Mehaffey
Keyword(s):  
High Speed ◽  
Shock Loading ◽  
Low Frequency ◽  
Dynamic Strain ◽  
Time Axis ◽  
Low Frequencies ◽  
Strain Measurements ◽  
Moving Vehicles ◽  
Machine Parts ◽  
Dynamic Strains

Abstract The measurement of dynamic strains of both high and low frequency give rise to a variety of problems in instrumentation. Two types of equipment and circuits designed and used by the authors are discussed in detail. The first type based on the amplitude-modulated method is for low frequencies from zero to about 15 per cent of the carrier frequency of 1025 cycles per sec. The equipment has application to strain measurements varying from static values to those produced in moving vehicles, various machine parts, structures such as crane bridges, in fact all strain measurements where the frequency is 150 cycles per sec or less. The second type of equipment discussed is a potentiometer type and is for high-frequency strain measurements from 100 cycles per sec to 8000 cycles per sec. This high-speed equipment is conveniently used for impact strain, such as produced in hammer blows, shock loading, forging equipment, and impact-factor determination. Both units are designed to be used with a cathode-ray oscillograph which lends itself to a variety of recording methods. The methods discussed include both the type where the time axis is obtained by sweeping the oscilloscope beam on a stationary film and where the time axis is obtained mechanically.

scholarly journals Comparison of waveform-derived corneal stiffness and stress-strain extensometry-derived corneal stiffness using different cross-linking irradiances: an experimental study with air-puff applanation of ex vivo porcine eyes

2020 ◽  
Vol 258 (10) ◽  
pp. 2173-2184 ◽  
Author(s):  
Robert Herber ◽  
Mathew Francis ◽  
Eberhard Spoerl ◽  
Lutz E. Pillunat ◽  
Frederik Raiskup ◽  
...  
Keyword(s):  
Experimental Study ◽  
Ex Vivo ◽  
Cross Linking ◽  
Displacement Curve ◽  
Stress Strain ◽  
Strain Measurements ◽  
Deflection Amplitude ◽  
Force Displacement ◽  
Stiffening Effect ◽  
Porcine Eyes

Abstract Purpose To assess corneal stiffening of standard (S-CXL) and accelerated (A-CXL) cross-linking protocols by dynamic corneal response parameters and corneal bending stiffness (Kc[mean/linear]) derived from Corvis (CVS) Scheimpflug-based tonometry. These investigations were validated by corneal tensile stiffness (K[ts]), derived from stress-strain extensometry in ex vivo porcine eyes. Methods Seventy-two fresh-enucleated and de-epithelized porcine eyes were soaked in 0.1% riboflavin solution including 10% dextran for 10 min. The eyes were separated into four groups: controls (n = 18), S-CXL (intensity in mW/cm2*time in min; 3*30) (n = 18), A-CXL (9*10) (n = 18), and A-CXL (18*5) (n = 18), respectively. CXL was performed using CCL Vario. CVS measurements were performed on all eyes. Subsequently, corneal strips were extracted by a double-bladed scalpel and used for stress-strain measurements. K[ts] was calculated from a force-displacement curve. Mean corneal stiffness (Kc[mean]) and constant corneal stiffness (Kc[linear]) were calculated from raw CVS data. Results In CVS, biomechanical effects of cross-linking were shown to have a significantly decreased deflection amplitude as well as integrated radius, an increased IOP, and SP A1 (P < 0.05). Kc[mean]/Kc[linear] were significantly increased after CXL (P < 0.05). In the range from 2 to 6% strain, K[ts] was significantly higher in S-CXL (3*30) compared to A-CXL (9*10), A-CXL (18*5), and controls (P < 0.05). At 8% to 10% strain, all protocols induced a higher stiffness than controls (P < 0.05). Conclusion Several CVS parameters and Kc[mean] as well as Kc[linear] verify corneal stiffening effect after CXL on porcine eyes. S-CXL seems to have a higher tendency of stiffening than A-CXL protocols have, which was demonstrated by Scheimpflug-based tonometry and stress-strain extensometry.

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