Force Measuring System for High-Precision Surface Characterization under Extreme Conditions

Force measuring is used in various surface characterization techniques such as indentation, scratch tests, tribological analysis, determination of gas content, etc. The main problems related with force measurement under extreme conditions have been analysed. A strategy that should be followed to solve these problems has been discussed and several examples of successive solutions that recently were developed by the authors are presented. The need to carry out the characterization under extreme conditions poses serious problems for the designers of the measuring systems that may include the incompatibility of the sensors with the test conditions, undesirable interactions with other components, stability, precision and uncertainty issues, the measurement range, etc. Resolving these problems must be based on a global approach in which the characterization system is considered as a whole, while the designer must analyse and solve the possible conflicts between the subsystems. The way how an appropriate force measuring system can be selected is described. The proposed method is illustrated by an example in which an indirect force measurement using optical fibre displacement sensor was used. Another example describes measuring system developed for vacuum high-temperature nanoindentation. At high temperature, proper heat management based on non-contact heating and laminar flow cooling system is mandatory to avoid experimental data being affected by external noise and thermal drift

Cholesterol and fatty acids oxidation in meat from three muscles of Massese suckling lambs slaughtered at different weights

Eighteen Massese male lambs fed mainly with maternal milk were slaughtered at 11, 14 and 17 kg. Samples of Longissimus dorsi (LD), Triceps brachii (TB) and Semimembranosus (Sm) muscles were collected. Total intramus- cular lipids were extracted by means of a mix- ture of chloroform methanol 2/1. Cholesterol content and its oxidation product (COP) were determined by a gas chromatography appara- tus equipped with an apolar 30 m column. Fatty acid oxidation was evaluated by means of thio- barbituric acid reactive substances (TBARS) extracting the sample with aqueous acidic solution. The effect of slaughter weight on oxi- dation of intramuscular lipids was found only in TB muscles. In this muscle the cholesterol content showed a decreasing trend, while the content of COPs significantly increased with the age of animals. Among the COPs, the 7- ketocholesterol and 7β-hydroxycholesterol were the most abundant, followed by α- and β- epoxy-cholesterol and cholestan-triol. The con- tent of TBARS did not vary owing to a similar fatty acid composition of intramuscular fat across weight of slaughter. In any case, the val- ues of TBARS did not reach the threshold of the detection of off-flavour in meat

High temperature nanoindentation up to 800°C for characterizing high temperature properties of materials

One of the primary motivations for development of instrumented indentation was to measure the mechanical properties of thin films. Characterization of thin film mechanical properties as a function of temperature is of immense industrial and scientific interest. The major bottlenecks in variable temperature measurements have been thermal drift, signal stability (noise) and oxidation of/condensation on the surfaces. Thermal drift is a measurement artifact that arises due to thermal expansion/contraction of indenter tip and loading column. This gets superimposed on the mechanical behavior data precluding accurate extraction of mechanical properties of the sample at elevated temperatures. Vacuum is essential to prevent sample/tip oxidation at elevated temperatures. In this poster, the design and development of a novel nanoindentation system that can perform reliable load-displacement measurements over a wide temperature ranges (from -150 to 800 °C) will be presented emphasizing the procedures and techniques for carrying out accurate nanomechanical measurements. This system is based on the Ultra Nanoindentation Tester (UNHT) that utilizes an active surface referencing technique comprising of two independent axes, one for surface referencing and another for indentation. The differential depth measurement technology results in negligible compliance of the system and very low thermal drift rates at high temperatures. The sample, indenter and reference tip are heated/cooled separately and the surface temperatures matched to obtain drift rates as low as 1nm/min at 800 °C without correction. Instrumentation development, system characterization, experimental protocol, operational refinements and thermal drift characteristics over the temperature range will be presented, together with a range of results on different materials. Please click Additional Files below to see the full abstract

Portevin‐Le Chatelier effect in AlMg3% studied using elevated temperature nanoindentation

The Portevin-Le Chatelier (PLC) is a plastic instability observed in different alloys, and particularly in aluminum alloys, which is characterized by a serrated flow during plastic deformation. The PLC effect originates from the competition between gliding of mobile dislocations and pinning of these dislocations by diffusing solute atoms. This dynamic strain hardening leads to a negative strain rate sensitivity which is often used to characterize or quantify the PLC effect. The PLC effect has been widely investigated in the case of stress-strain curves obtained in macroscopic uni-axial tests. However, in the case of the aluminum matrix composites Al/AlCuFe, it has been observed that copper atoms diffuse during the material synthesis form the reinforcement particles to the aluminum matrix. The aluminum matrix thus presents a heterogeneous concentration of copper atoms leading to local PLC effect. Nanoindentation test is the best way to characterize locally this mechanical effect. However, strain rate is not a convenient parameter for nanoindentation tests since the complex strain field below the indent, as well as the increase of the contact area during the test, makes difficult the definition a single strain value. Another way to investigate a local PLC effect would be thus the perform nanoindentation tests at different temperatures rather than different strain rates. This poster will present experimental results from elevated temperature nanoindentation studies on an AlMg3% alloy, used as a model material for easy comparison with uniaxial tests, in the temperature range from 25-300°C. The experiments were performed in displacement controlled mode in a recently developed vacuum high temperature nanoindenter based on active surface referencing and non-contact tip and sample heating. In this configuration, the PLC effect appears as successive load drops on the loading curves. The temperatures of the tip and the sample surface were calibrated and matched in order to minimize thermal drift. With increasing temperature, the magnitude of load drop decreased whereas its occurrence frequency increased. The load drop magnitude and its occurrence frequency were statistically analyzed for different temperatures of testing. The results will be discussed in terms of an expanding plastic volume beneath the indenter interacting with the solute atoms in the complex stress field of the indenter

Multivariate factor analysis of milk fatty acid composition in relation to the somatic cell count of single udder quarters

The present study investigated whether the fatty acid composition of milk changes in relation to an increase in the milk somatic cell count (SCC) of separate udder quarters. We investigated the potential of multivariate factor analysis to extract metabolic evidence from data on the quantity and quality of milk of quarters characterized by different SCC levels. We collected data from individual milk samples taken from single quarters of 49 Italian Holstein cows from the same dairy farm. Factor analysis was carried out on 64 individual fatty acids. In line with a previous study on multivariate factor analysis, a variable was considered to be associated with a specific factor if the absolute value of its correlation with the factor was ≥0.60. Seven factors were extracted that explained the following groups of fatty acids or functions: de novo synthesis, energy balance, uptake of dietary fatty acids, biohydrogenation, short-chain fatty acids, very long chain fatty acids, and odd- and branched-chain fatty acids. An ANOVA of factor scores highlighted the significant effects of the SCC level on de novo fatty acids and biohydrogenation. The de novo fatty acid factor decreased significantly with a high level of SCC, from just 10,000 cells/mL, whereas the biohydrogenation factor showed a significantly higher level in quarters with SCC levels greater than 400,000 cells/mL. This statistical approach enabled us to reduce the number of variables to a few latent factors with biological significance and to represent groups of fatty acids with a common origin and function. Multivariate factor analysis could therefore be key to studying the influence of SCC on the lipid metabolism of single quarters. This approach also demonstrated the metabolic differences between quarters of the same animal showing a different level of SCC

Indirect contact pressure evaluation on pneumatic rod seals

This paper deals with the experimental evaluation of contact pressure at the interface between an elastomeric rod seal for pneumatic cylinders and its metallic counterpart without interposing any intrusive measuring device. A new test bench, which is able to measure the radial force exerted by a rod seal displaced at constant velocity on a sensorized portion of a cylinder rod over time, was designed and manufactured. The seal was pressurised to reproduce actual working conditions. A data postprocessing methodology was developed for an indirect evaluation of contact pressure starting from the experimental data set of the radial force exerted by the seal on the rod. At first, the measured radial force signal was filtered and properly fitted obtaining a differentiable function; then, contact pressure distribution was computed as a function of radial force time derivative, seal velocity and rod diameter. Preliminary experimental results are presented

Temporal changes of conjugated linoleic acid in milk from Sarda ewes with different milk fat secretion ability

Individual milk samples were weekly collected from 48 ewes during eight weeks. Ewes were at the second month of lactation and they were fed the same dietary regimen. The animals were grouped according to the amount of daily milk fat yield: A) 38-57g/d, B) 58-63g/d, C) 64-73g/d, D) 75-110g/d. Milk from group D showed a higher content of FA from C4 to C10 and a lower content of monounsaturated FA (MUFA) and conjugated linoleic acids (CLA) than Group A (+12%, -11%, and -18%, for C4 to C10, MUFA and CLA, respectively), while Group B and C showed intermediate values. CLA content increased with days of lactation in a similar way for all groups. The mean correlation among all records within each individual lactation was 0.45 for CLA content. Six milk FA pair ratios representing a proxy for SCD activity were also evaluated: group A showed higher values of FA ratios than Group D (+26% on average for all FA pairs). In conclusion, increasing ability of daily milk fat yield was associated with lower milk content of MUFA and CLA and higher content of FA from C4 to C10

Designing statistical models for holstein rearing heifers’ weight estimation from birth to 15 months old using body measurements

Body measurements could be used to estimate body weight (BW) with no need for a scale. The aim was to estimate heifers weight based on their body dimension characteristics. Twenty-five Holstein heifers represent the study group (SG); another 13 animals were evaluated as a validation group (VG). All the heifers were weighed (BW) and their wither height (WH), shin circumference (SC), heart girth circumference (HG), body length (BL), hip width (HW) and body condition score (BCS) were measured immediately after birth, and then weekly until 2 months and monthly until 15 months old. Equations were built with a stepwise regression in order to estimate the BW at each time using body measures for the SG. A linear regression was applied to evaluate the relationship between the estimated BW and the real BW. Equations found were to be statistically significant (r2 = 0.688 to 0.894; p < 0.0001). Three variables or fewer were needed for BW estimation a total of 11/23 times. Regression analysis indicated that the use of HG was promising in all the equations built for BW estimation. These models were feasible in the field; further studies will evaluate possible modifications to our equations based on different growing rate targets

Transcriptome Adaptation of the Ovine Mammary Gland to Dietary Supplementation of Extruded Linseed

Several dietary strategies were adopted to reduce saturated fatty acids and increase beneficial fatty acids (FA) for human health. Few studies are available about the pathways/genes involved in these processes. Illumina RNA-sequencing was used to investigate changes in the ovine mammary gland transcriptome following supplemental feeding with 20% extruded linseed. Comisana ewes in mid-lactation were fed a control diet for 28 days (control period) followed by supplementation with 20% DM of linseed panel for 28 days (treatment period). Milk production was decreased by 30.46% with linseed supplementation. Moreover, a significant reduction in fat, protein and lactose secretion was also observed. Several unsaturated FAs were increased while short and medium chain saturated FAs were decreased by linseed treatment. Around four thousand (1795 up- and 2133 down-regulated) genes were significantly differentially regulated by linseed supplementation. The main pathways affected by linseed supplementation were those involved in the energy balance of the mammary gland. Principally, the mammary gland of fed linseed sheep showed a reduced abundance of transcripts related to the synthesis of lipids and carbohydrates and oxidative phosphorylation. Our study suggests that the observed decrease in milk saturated FA was correlated to down-regulation of genes in the lipid synthesis and lipid metabolism pathways

Pushing the envelope for high temperature nanoindentation measurements

One of the primary motivations for development of instrumented indentation was to measure the mechanical properties of thin films and individual phases/grains. Characterization of thin film mechanical properties as a function of temperature is of immense industrial and scientific interest. The major bottlenecks in elevated temperature measurements have been thermal drift, signal stability (noise) and oxidation of the surfaces. Thermal drift is a measurement artifact that arises due to thermal expansion/contraction of indenter tip and loading column. This gets superimposed on the mechanical behavior data precluding accurate extraction of mechanical properties of the sample at elevated temperatures. Vacuum is essential to prevent sample/tip oxidation and to push the envelope for high temperature testing. This poster will present the high temperature vacuum nanoindenter designed at Anton Paar that can perform reliable load-displacement measurements over a wide temperature ranges (up to 700 °C). This system is based on the Ultra Nanoindentation Tester (UNHT) that utilizes an active surface referencing technique comprising of two independent axes, one for surface referencing and another for indentation. The differential depth measurement technology results in negligible compliance of the system due to symmetric architecture and very low thermal drift rates at high temperatures as the thermal drift is actively compensated by the surface referencing technology. The sample, indenter and reference tip are heated separately and the surface temperatures matched to obtain drift rates as low as 10 nm/min at 700 °C on copper Test results on standard calibration materials like fused silica and oxygen free high conductive copper, used for validating the system, will be presented. The developed experimental protocol for minimizing thermal drift and the challenges associated with high temperature testing will be discussed