Non-Contacting Extensometry Excels in Strain Measurement

The correct testing of raw materials in chemical production can further improve the quality of chemical production, which is the basic prerequisite for ensuring the quality of chemical products. At present, in the testing stage of chemical raw materials, the application of chemical analysis technology is very important to improve the quality and efficiency of chemical raw materials. Therefore, it is necessary to thoroughly study the technical characteristics of chemical analysis and its specific application in chemical testing. The study can provide scientific and accurate technical guarantees for the chemical testing process and results, and meet the actual needs of chemical raw material testing.

A bioavailable nutrient has the potential to be utilized when ingested. Ideally, the nutrient requirements of animals and the nutrient concentrations of feedingstuffs should be expressed in terms of bioavailable units. Bioavailability is an abstract concept which cannot be measured but it can be estimated. The purpose of this review is to describe, evaluate and compare procedures used to estimate the concentrations of bioavailable amino acids (BAA) in feedingstuffs for pigs and poultry. Accurate and precise measurement of total amino acid (AA) concentrations is of fundamental importance to many assays. Problems are encountered both in making the AA available for measurement (hydrolysis) and in the measurement procedures. There is need for standardization of methodology but until this is achieved caution must be exercised when comparing data obtained by different techniques or even from different laboratories. In vitro assays for BAA are relatively fast and can be made without access to animals. Enzymic digestion has the potential to be a good estimator of BAA but is constrained by a lack of information about the bioavailabilities of the peptides which are liberated. Chemical assays and dye binding produce data which sometimes, but not always, correlate with biological estimates of BAA. The future of such assays seems to be in quality control where comparisons are made among samples within ingredients. Among the indirect biological assays, those based on microbial growth have received the most attention. The major weakness of such assays resides in the difference between animal and microbe in the ability to utilize peptides. Plasma free amino acids are not satisfactory estimators of BAA although they can help to identify limiting AA in feedingstuffs. Nitrogen digestion lacks the sensitivity to be a predictor of BAA. Growth assays are thought by many to be the ultimate measure of bioavailability but in fact they measure utility which is not the same. Nevertheless, growth assays can provide valuable estimates of BAA providing that their limitations are understood. The assays are expensive and slow and the results can be affected by many variables including changes in nutrient concentrations when a test material is added to an assay diet. Much of the review is devoted to balance experiments which require great care and attention to detail if reliable, reproducible data are to be obtained. Procedures have been refined during many years of use and with the advent of new equipment and techniques. Concern is currently focussed on corrections for metabolic and endogenous losses and on the effects of the microflora of the alimentary tract. Recent developments have increased assay efficiency, particularly with poultry. The balance experiment provides BAA estimates, that can be used effectively in diet formulation, at a much faster rate than growth assays. The final section of the review makes comparisons among various methods of estimating BAA. Interspecies comparisons are useful because they provide guidance when attempting to apply data derived with one species to formulate diets for another. The search for a single assay which provides data applicable to several species is a worthwhile objective. In the meantime, there are many assays used to estimate BAA which have specific applications and limitations. Key words: Pigs, poultry, amino acids, assay methodology, feedingstuffs, review

In mechanical characterization methods, the mechanical properties of multiple material test specimens are measured to determine the probabilistic characteristics of the material's properties through statistical inference. Several of these methods require the measurement of deformations, and to do so, they rely on local strain measuring techniques, such as bonded strain gages and extensometers. In this study, we show that for non-crimp fabric laminates, local strain measurements acting as proxies of global laminate strain contain a random strain measurement error. Furthermore, we demonstrate that this strain measurement error can significantly reduce the accuracy of characterization methodologies for non-crimp fabric laminates. The strain measurement error pollutes the mechanical property measurements on laminate test specimens, leading to inaccurate statistical inferences. Because the strain measurement error is random, the inferences regarding the mechanical properties may occasionally be conservative or non-conservative with respect to the inference that would have been made if there was no strain measurement error. The results presented in this study are of importance because over-conservative mechanical properties can lead to unnecessarily heavy structures, and non-conservative ones may lead to unsafe structures, endangering life property and the environment. Both scenarios were discussed along with their likelihood and possible consequences.

The design of sample geometries and the measurement of small strains are considered the main challenges when testing composite materials at high strain rates using the split Hopkinson bar technique. The aim of this paper is to assess two types of tensile sample geometries, namely dog-bone and straight strip, in order to study the tensile behaviour of basalt fibre reinforced composites at high strain rates using the split Hopkinson bar technique. 2D Digital image correlation technique was used to study the distribution of the strain fields within the gauge section at quasi-static and dynamic strain rates. Results showed that for the current experiments and the proposed clamping techniques, both sample geometries fulfilled the requirements of a valid split Hopkinson test, and achieved uniform strain fields within the gauge section. However, classical Hopkinson analysis tends to overestimate the actual strains in the gauge section for both geometries. It is, therefore, important to use a local deformation measurement when using these 2 geometries with the proposed clamping technique.

A new strain gauge-based triaxial extensometer (radial extensometers x, y and axial extensometer z) is presented to improve the volumetric strain measurement in a hydro-compression loading test for foam materials. By the triaxial extensometer, triaxial deformations of the foam specimen can be measured directly, from which the volumetric strain is determined. Sensitivities of the triaxial extensometer are predicted using a finite-element model, and verified through experimental calibrations. The axial extensometer is validated by conducting a uniaxial compression test in aluminium foam and comparing deformation measured by the axial extensometer to that by the advanced optical 3D deformation analysis system ARAMIS; the result from the axial extensometer agrees well with that from ARAMIS. A new modus of two-wire measurement and transmission in a hydrostatic environment is developed to avoid the punching and lead sealing techniques on the pressure vessel for the hydro-compression test. The effect of hydrostatic pressure on the triaxial extensometer is determined through an experimental test. An application in an aluminium foam hydrostatic compression test shows that the triaxial extensometer is effective for volumetric strain measurement in a hydro-compression loading test for foam materials.

Methodology improvement of bulk compressive creep test: Deformation measurement and loading rate

Mechanical properties can be determined for all types of materials whether metals, ceramics, polymers, or composites. The material is hence used for specific purpose based on its property. Selection for an appropriate material and treatments for a particular application requires material testing. A material testing helps us to understand and compute whether a specific material is suitable for a particular application. A wide range of materials are available in market for various uses. The choice of material to the most appropriate selection for the intended use can be made easier with the help of material testing. In material characterization, the analysis of material properties and composition is useful in failure investigation and other problems, and in validating manufacturing processes. There are various testing methods available to test the materials. They are classified into two categories destructive testing and non-Destructive Testing (NDT). Present work focuses on superiority of NDT over destructive method and discusses about novel NDT material testing technique called Laser Based Ultrasonics (LBU) technique which is one of the NDT methods for testing and material characterization.

The classical specification of elastic/plastic or rigid/plastic response in metals is reformulated in generalized variables. The allowed measures of strain are sets of any geometric magnitudes that jointly determine the shape of a material element; the allowed measures of stress are generated by work-conjugacy. The choice of variables affects the parameters and qualitative features of the constitutive framework; these dependences are made explicit by concise formulae of transformation.Eigenstates intrinsic to the material are considered wherein the strain can change while the conjugate stress is either stationary or coupled differentially with the strain. Such configurations are associated with incipient branching of the strain response to a prescribed variation of the conjugate stress. Sensitivity to the loading environment is evaluated for both elastic/plastic and rigid/plastic materials. This synoptic approach to eigenproblems is illustrated in the context of materials testing.

The use of strain gages on composite materials is an essential element in most mechanical property characterization methods. A recent summary, on the state of the art in strain gage technology, was written by C.C. Perry, [ 1] , one of the leading authorities in the field. Dr. Perry concludes that there are fringe areas in strain gage technology which have been only partially explored such as large strains, reinforcement effects, thermally and hygroscopically anisotropic test materials, etc. They require a much more thorough examination if accuracies of ± 10 % or better are to be reliably achieved in strain measurements on plastic based structural materials.KeywordsPercentage ErrorStrain GageAxial StrainFiber DirectionTransverse StrainThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The paper presents a method for the surface shape and strain measurement applied in the determination of metal flow and product quality. Accurate determination of these characteristics in the sheet metal forming operation is extremely important, especially in automotive applications. However, the sheet metal forming is a very complex manufacturing process, and its success depends on many factors. This involves a number of tests that should be carried out to find optimal, yet cost-effective solutions. In this study the author discusses the investigations that are focused on better understanding of the strain values and their distribution in a product, and checking if they do not exceed certain limit resulting in the loss of stability. The hydraulic bulge test was identified as a method most applicable in these investigations, where both theoretical and experimental analysis was conducted. First, the presented solution in the field of reconstruction of three-dimensional (3D) objects significantly expands the capabilities of the analysis, compared with the solutions existing so far. Second, a new method for the 3-dimensional geometry and strain measurement based on laser scanning technique is presented. Next, the image acquisition process and digital image correlation (DIC) are presented to recognize and analyze the objects taken from camera. The 3D shape and strain analysis presented in this paper offers a valuable tool in the metal products quality control, along with a complete testing equipment for maximum strain calculation just before cracking. The computer measurement system is directly connected to the hydraulic bulge test apparatus, thus providing fast and accurate results for material testing and process analysis.

We have developed a Fabry–Perot extensometer that is able to operate at high temperature (up to 400 °C), for in pile experiments in material testing reactor, under high neutron and gamma flux. For that purpose, we have revised the basic scheme of an extrinsic Fabry–Perot interferometer (EFPI) to limit the effects of radiation and especially of the fast neutron fluence and to adapt the sensor to high temperature. After a description of the sensor and its operation, we present, in this article, two types of tests that were carried out to check the accuracy of the sensor at high temperature. First, four sensors are fixed either on stainless steel plates or on tantalum plates and the temperature is raised from room temperature to 400 °C. Knowing the thermal expansion of both the supports and the sensor parts, it is possible to predict the expected variation of the sensor output. The comparison between the predicted and experimental outputs provides the information about the accuracy of the sensor. Second, we performed high-temperature tensile testing at 300 °C and 350 °C. The Fabry–Perot measurements are compared, in the elastic domain, with the expected strain given by Hooke’s law, and on a larger strain domain, with the measurements of a high-temperature axial extensometer. The experiments and the results are presented. The error appears to be limited to about $1~\mu \text{m}$ when the strain is low (0.1%) and can be of few micrometers on a larger range (up to 2%). Strain measurements up to more than 5% are also reported.

The stress distributions and strength of adhesive butt joints of pipes of which the both ends are closed are analyzed by using an axisymmetric finite element method (FEM). The interface stress distributions are demonstrated. The joint strength is estimated using the interface stress distribution. The butt adhesive joints with small flanges and without flanges were manufactured. Rupture tests of the adhesive butt joints of pipes subjected to internal pressure by hydraulic pump were carried out. In addition, rupture tests of the joints were also conducted by using a material testing machine. Strain measurements were carried out on the joints. It is found that the stress singularity occurs at the inner and the outer edges of the interfaces. It is seen that the stress singularity is larger at the inner edge than that at the outer edge. The strength of the joints is evaluated using 95% non-rupture probability of the rupture test results. As a result, it is found that the strength of the joints with flanges are larger than that without flanges. Furthermore, it is observed that the strength of the joints with flanges is not proportional to the bonded area of the joints. The estimated values of the joint strength are in fairly good agreement with the experimental results.

This study examined the Barkhausen noise (BN) response of carburising case-hardened steel with varying tempering stages. The test material was loaded in bending and in alternating loading. The aim of the study was to obtain relevant multiparameter BN data from different loading conditions and to investigate the effect of applied stress on the BN response. The test bar series was made from case-hardened steel. Different tempering parameters were used to vary the surface hardness and the surface residual stresses of the studied series of test bars. In the bending tests, the samples were subjected to incrementally applied loading in the purely elastic deformation region. In addition, uniaxial stepwise loading with tensile and compressive stress was applied to selected samples simultaneously with the BN measurements. The BN measurements were performed under different loading conditions along with X-ray diffraction strain measurements in bending. The results revealed linear behaviour between the reciprocal root mean square value and the stress values obtained with strain gages and X-ray diffraction for the tempered samples.

Hands-on experiences in biomechanics and biomaterials courses are an important part of biomedical engineering education. Curricula of those courses often include laboratory modules on material testing and characterization. Unfortunately, large and expensive mechanical testing equipment may not be available to all students, thus limiting students’ access to actual hands-on experience. Here, we introduce an open, accessible, and affordable mechanical test device that ensures that every student gets their hands on test equipment and a test specimen. In fact, the device has a small form factor, is inexpensive, and can therefore be taken home. The device is built with low-cost components and 3D-printed parts for a total cost of less than $45. The device also makes use of each student’s cell phone camera for optical strain measurements, thereby avoiding the need for expensive imaging equipment. In addition to the device, we also introduce a rich set of supplementary materials that make adoption and application by educators and students as easy as possible. A first experience in a 20-student biomedical engineering technical elective class has demonstrated ease of use and anecdotally confirms the device and material’s usefulness in practical teaching. However, more formal evaluation is needed to demonstrate that our test device and materials enhance laboratory teaching.

The paper outlines the results of the development of the test tools to be used in shear tests of thin-wall composite materials under high temperatures. The calculation methods and the configuration of the newly developed test tools are discussed. Drawings and the general outline of the test tools are shown. Analysis of the experimental data and the stress strain curves obtained for test samples of the thin-wall composite material are presented. With the newly developed test tools, it is possible to perform shear tests of test samples of thin-wall composite materials over a wide temperature range, namely, under RT to 2000 ºC and even higher temperatures.