Approaches to Synchronise Conventional Measurements with Optical Techniques at High Strain Rates

2011 ◽  
Vol 70 ◽  
pp. 75-80 ◽  
Author(s):  
Duncan A. Crump ◽  
Janice M. Dulieu-Barton ◽  
Marco L. Longana
Keyword(s):  
Polymer Composites ◽  
High Speed ◽  
High Strain ◽  
Image Correlation ◽  
Test Machine ◽  
Strain Rates ◽  
High Strain Rates ◽  
Optical Techniques ◽  
Specific Loading ◽  
Military Applications

Polymer composites are increasingly being used in high-end and military applications, mainly due to their excellent tailorability to specific loading scenarios and strength/stiffness to weight ratios. The overall purpose of the research project is to develop an enhanced understanding of the behaviour of fibre reinforced polymer composites when subjected to high velocity loading. This is particularly important in military applications, where composite structures are at a high risk of receiving high strain rate loading, such as those resulting from collisions or blasts. The work described here considers an approach that allows the collection of full-field temperature and strain data to investigate the complex viscoelastic behaviour of composite material at high strain rates. To develop such a data-rich approach digital image correlation (DIC) is used to collect the displacement data and infra-red thermography (IRT) is used to collect temperature data. The use of optical techniques at the sampling rates necessary to capture the behaviour of composites subjected to high loading rates is novel and requires using imaging systems at the far extent of their design specification. One of the major advantages of optical techniques is that they are non-contact; however this also forms one of the challenges to their application to high speed testing. The separate camera systems and the test machine/loading system must be synchronised to ensure that the correct strain/temperature measurement is correlated with the correct temporal value of the loading regime. The loading rate exacerbates the situation where even at high sampling rates the data is discrete and therefore it is difficult to match values. The work described in the paper concentrates on investigating the possibility of the high speed DIC and synchronisation. The limitations of bringing together the techniques are discussed in detail, and a discussion of the relative merits of each synchronisation approach is included, which takes into consideration ease of use, accuracy, repeatability etc.

Experimental Studies of the Behaviour at High Strain Rates of Unfilled and Filled Polypropylenes

2006 ◽  
Vol 3-4 ◽  
pp. 363-368 ◽  
Author(s):  
N. Temimi ◽  
Noelle Billon
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
High Strain ◽  
Experimental Studies ◽  
Young Modulus ◽  
Video Camera ◽  
Image Correlation ◽  
Strain Rates ◽  
High Strain Rates ◽  
Low Velocity

Thermo mechanical behaviour of unfilled and filled polypropylenes are studied in tension from 10-4 to 102 s-1. Complementary low velocity compression and shear tests are also performed. A high-speed video camera (up to 2500 frames/s) combined with image analysis, image correlation and an infra red pyrometer allow measuring 3D-strain fields and temperature during tests. Thus, data can be processed without restrictive assumptions. Beside usual (for polymers) temperature and strain rate sensitivities it is found that plastic deformation in these materials does not obey incompressibility assumption. Voiding damage is evidenced in the polymer matrix by SEM observations that result in volume change and significant decrease in Young modulus for both materials. Moreover, an increase in the temperature of more than 10 °C is observed and is likely to modify the behaviour of each material at high strain rates. Shear and compression measurements demonstrate that yield criteria and constitutive equation depend on loading. It is concluded that apparent yield stress in semi-crystalline polypropylene can be a result of a combination of “non strain rate sensitive” “non-cohesive mechanisms” and “strain rate sensitive” “cohesive mechanisms”. Experimental characterisation on polymers should then be revisited as most of the usual assumptions are invalid and non monotonic tests should be generalized.

Mechanical Behavior of Sn1Ag0.5Cu and Sn3Ag0.5Cu Alloys at High Strain Rates

2012 ◽  
Author(s):  
Pradeep Lall ◽  
Sandeep Shantaram ◽  
Jeff Suhling ◽  
David Locker
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Prolonged Exposure ◽  
High Strain ◽  
Split Hopkinson Pressure Bar ◽  
Image Correlation ◽  
Constitutive Behavior ◽  
Strain Rates ◽  
High Strain Rates ◽  
Test Technique

Electronics may experience high strain rates when subjected to high g-loads of shock and vibration. Material and damage behavior of electronic materials at high strain rates typical of shock and vibration is scarce. Previously studies have shown that second-level interconnects have a high propensity for failure under shock and vibration loads in fine pitch electronics. Exposure to shock and vibration is common in a variety of consumer environments such as automotive and portable electronics. The low strain-rate properties of commonly used SnAgCu solders, including Sn1Ag0.5Cu and Sn3Ag0.5Cu, have been found to evolve with time after prolonged exposure to high temperatures. High strain rate properties of leadfree solder alloys in the strain-rate range of 1–100 sec−1 are scarce. Previous attempts at characterizing the high strain rates properties have focused on the use of the Split Hopkinson Pressure Bar (SHPB), which enables measurements of strain rates in the neighborhood of 1000 per sec. In this paper, a new test-technique developed by the authors has been presented for measurement of material constitutive behavior. The instrument enables attaining strain rates in the neighborhood of 1 to 100 per sec. Tests are conducted at strain rates 10, 35 and 50 per sec. High speed cameras operating at 75,000 fps have been used in conjunction with digital image correlation for the measurement of full-field strain during the test. Constancy of cross-head velocity has been demonstrated during the test from the unloaded state to the specimen failure. Solder alloy constitutive behavior has been measured for SAC105, SAC305 solders. Non-linear Ramberg-Osgood model has been used to fit the material data. The Ramberg-Osgood model available in Abaqus has been used for tensile test simulation and to correlate with DIC based experimental strain data.

scholarly journals Dynamic Tensile Testing of Needle-Punched Nonwoven Fabrics

2020 ◽  
Vol 10 (15) ◽  
pp. 5081
Author(s):  
Francisca Martínez-Hergueta ◽  
Antonio Pellegrino ◽  
Álvaro Ridruejo ◽  
Nik Petrinic ◽  
Carlos González ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Tensile Testing ◽  
High Speed ◽  
High Strain ◽  
Nonwoven Fabric ◽  
Image Correlation ◽  
High Speed Photography ◽  
Strain Rates ◽  
High Strain Rates ◽  
Nonwoven Fabrics

The tensile testing of a needle-punched nonwoven fabric is presented. A high-sensitivity Split-Hopkinson Tensile Bar device was specifically designed for this purpose. The strain gauge measurements were combined with high-speed photography and Digital Image Correlation to analyse the deformation micromechanisms at high strain rates. The experimental set-up allowed to determine the wave propagation velocity of the as-received nonwove fabric, the evolution of the strain field with deformation and the wave interaction inside the fabric. The deformation was accommodated by the same micromechanisms observed during quasi-static tensile testing and ballistic impact, which comprised fibre straightening, rotation and sliding. Heterogeneous strain fields were developed in the nonwoven fabric as a result of the non-linear pseudoplastic response of the fabric and the internal dissipation due to the frictional deformation micromechanisms, preventing the propagation of high magnitude strain waves into the specimen. Additionally, the output forces were analysed to determine the influence of high-strain rates in the mechanical response of the nonwoven fabric, finding an increment of the stiffness for low applied strains under dynamic loading. These findings provide the basis to develop strain-rate dependent constitutive models to predict wave propagation in needle-punched nonwoven fabrics when subjected to impact loads.

Pb-free PBGA Design Points to Improve Handling Robustness

2012 ◽  
Vol 2012 (1) ◽  
pp. 000110-000118 ◽  
Author(s):  
Isabel de Sousa ◽  
Brian Roggeman ◽  
Oswaldo Chacon ◽  
Niki Spencer ◽  
Mamoru Ueno
Keyword(s):  
High Speed ◽  
Solder Joints ◽  
High Strain ◽  
Strain Rates ◽  
Process Variables ◽  
Flexural Stress ◽  
High Strain Rates ◽  
Ball Shear ◽  
Laminate Design ◽  
Free Solder

Pb-Free BGA solder joints are more brittle and more susceptible to interfacial fails than the leaded versions. These brittle failures typically occur if the modules are subjected to high strain rates through module handling impacts or PCB flexural stress. The high speed ball shear technique is a useful method to submit solder joints to high strain rates in a controlled manner to emulate the levels of strain the BGAs may see in handling. This measurement technique was used to evaluate different laminate design and process variables on organic laminate substrates to create a more robust Pb-Free solder joint. Experiments were conducted to evaluate the effects and interactions of laminate, module assembly process, SAC alloy composition, and thermal treatments. Modulations of shear speed and shear angle made it possible to observe transitions from ductile to brittle solder fractures. The high speed ball shear method was successful to differentiate subtle effects resulting from different design points and process variables. The copper composition in the PbFree solder alloy, thermal history, and geometric factors such as solder volume, solder resist opening and solder resist thickness all had measurable impacts on the shear strength and transition point of ductile to brittle failure. Some BGA configurations have also been tested in reliability, namely in thermal cycling, and were shown to meet application requirements. Optimal design points can therefore be applied to enhance handling robustness without compromising on reliability.

Extensional Properties of Coating Colors at High Strain Rates

2003 ◽  
Author(s):  
Alfa Arzate ◽  
Gabriel Ascanio ◽  
Pierre J. Carreau ◽  
Philippe A. Tanguy
Keyword(s):  
Shear Viscosity ◽  
High Speed ◽  
High Strain ◽  
Newtonian Fluids ◽  
Extensional Viscosity ◽  
Strain Rates ◽  
High Strain Rates ◽  
Paper Coating ◽  
Trouton Ratio ◽  
The Relationship

Paper coating fluids also called colors are concentrated aqueous suspensions composed mainly of mineral pigments, thickeners, binders and dispersing agents. They are applied onto moving paper web for improving the optical and printing properties. Roll coating is one of the most used technologies for paper coating, however jet coating is currently a promising technology for high-speed processes. Coating colors are submitted to high strain rates in both roll or jet coaters, therefore the extensional viscosity plays a major role in the process. An orifice flowmeter was used for measuring the extensional properties of complex rheology fluids such as coating colors. The principle of this flowmeter is based on the relationship between pressure drop and the flow rate of fluid passing through a small orifice. The flowmeter was firstly calibrated in terms of a dimensionless Euler number as a function of the Reynolds number with Newtonian fluids. The calibration curve was then used to determine the apparent extensional viscosity of coating colors. Results of extensional properties of paper coating colors are presented and compared to shear viscosity. The ratio of extensional to shear viscosity (Trouton ratio) for some coating colors was shown to exceed considerably the theoretical value of 3 expected for Newtonian fluids.

Characterization of a Ferritic Stainless Sheet Steel in Simple Shear and Uniaxial Tension at Different Strain Rates

2011 ◽  
Author(s):  
Matti Isakov ◽  
Jeremy Seidt ◽  
Kauko O¨stman ◽  
Amos Gilat ◽  
Veli-Tapani Kuokkala
Keyword(s):  
Uniaxial Tension ◽  
Simple Shear ◽  
High Strain ◽  
Image Correlation ◽  
Materials Testing ◽  
Strain Rates ◽  
Test Results ◽  
High Strain Rates ◽  
Stress Strain

In this study the mechanical properties of ferritic stainless steel EN 1.4521 (AISI 444) were characterized in uniaxial tension and simple shear. The specimen geometries were designed so that tests could be carried out both with a conventional uniaxial materials testing machine and at high strain rates with the Tensile Hopkinson Split Bar method. During the tests, specimen surface deformation was measured using a three dimensional digital image correlation technique based on a two-camera stereovision setup. This technique allowed direct measurement of the specimen gauge section deformation during the test. Test results indicate that the selected approach is suitable for large strain plastic deformation characterization of ductile metals. The stress-strain data obtained from the simple shear tests shows a correlation with the tensile test results according to the von Mises effective stress-strain criterion. Since necking is absent in shear, test data can be obtained at considerably higher plastic strains than in tension. However, the final fracture occurs under a complex loading mode due to the distortion of the specimen geometry and multiaxial loading introduced by the simple shear arrangement. Test results also show that reliable material data can be obtained at high strain rates.

Development of a Time-Resolved Catadioptric Stereo Digital Image Correlation Technique for the Study of Blast Loading of Composite Material Structures

2011 ◽  
Author(s):  
Douglas Jahnke ◽  
Yiannis Andreopoulos
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
High Strain ◽  
Blast Loading ◽  
Image Correlation ◽  
Time Dependent ◽  
Correlation Technique ◽  
Strain Rates ◽  
Flat Plates ◽  
High Strain Rates

Impingement of blast or shock waves on structures is characterized by a substantial transient aerodynamic load that develops over the short time associated with the shock reflection time scale. This mutual interaction between the shock wave and the structure can cause significant deformation of the structure and high strain rates within the material resulting in damage. While accelerometers, strain gages and other single point measurement probes and their corresponding techniques can provide valuable information of the local displacement and strain during blast loading, better understanding of the complex phenomena involved in these interactions require time dependent information acquired simultaneously from multi points on the structure. Digital Image Correlation is a full-field noncontact optical technique which can provide time dependent information of the displacement of the structure and the resultant high strain rates generated during the loading. The present setup consists of a single high-frame-rate camera which can accommodate two simultaneous stereo images of the deforming structure on its CMOS chip. Four different planar mirrors, appropriately positioned, provide the stereo views of the specimen captured on the chip. The present layout offers several advantages over traditional systems with two different cameras. First, it provides identical system parameters for the two views which minimizes their differences and thus facilitating robust stereo matching. Second, it reduces calibration time since only one camera is used and third its cost is substantially lower than the cost of a system with two cameras. The technique is being developed and tested in a large scale shock tube facility during loading by shock/blast wave of various impulses. The specimens used are flat plates made of high-alloy steel, aluminum or composite materials. In the present paper the development of the technique will be described and preliminary results of qualification tests will be presented and discussed.

scholarly journals Use of simulated experiments for material characterization of brittle materials subjected to high strain rate dynamic tension

2017 ◽  
Vol 375 (2085) ◽  
pp. 20160168 ◽  
Author(s):  
Bratislav Lukić ◽  
Dominique Saletti ◽  
Pascal Forquin
Keyword(s):  
High Speed ◽  
Dynamic Range ◽  
High Strain ◽  
Experimental Testing ◽  
Brittle Materials ◽  
Strain Rates ◽  
High Strain Rates ◽  
Extrinsic Factors ◽  
Full Field ◽  
Ultra High Speed

Rapid progress in ultra-high-speed imaging has allowed material properties to be studied at high strain rates by applying full-field measurements and inverse identification methods. Nevertheless, the sensitivity of these techniques still requires a better understanding, since various extrinsic factors present during an actual experiment make it difficult to separate different sources of errors that can significantly affect the quality of the identified results. This study presents a methodology using simulated experiments to investigate the accuracy of the so-called spalling technique (used to study tensile properties of concrete subjected to high strain rates) by numerically simulating the entire identification process. The experimental technique uses the virtual fields method and the grid method. The methodology consists of reproducing the recording process of an ultra-high-speed camera by generating sequences of synthetically deformed images of a sample surface, which are then analysed using the standard tools. The investigation of the uncertainty of the identified parameters, such as Young's modulus along with the stress–strain constitutive response, is addressed by introducing the most significant user-dependent parameters (i.e. acquisition speed, camera dynamic range, grid sampling, blurring), proving that the used technique can be an effective tool for error investigation. This article is part of the themed issue ‘Experimental testing and modelling of brittle materials at high strain rates’.

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