Analysis of machining-induced residual stresses of milled aluminum workpieces, their repeatability, and their resulting distortion

Machining-induced residual stresses (MIRS) are a main driver for distortion of thin-walled monolithic aluminum workpieces. Before one can develop compensation techniques to minimize distortion, the effect of machining on the MIRS has to be fully understood. This means that not only an investigation of the effect of different process parameters on the MIRS is important. In addition, the repeatability of the MIRS resulting from the same machining condition has to be considered. In past research, statistical confidence of MIRS of machined samples was not focused on. In this paper, the repeatability of the MIRS for different machining modes, consisting of a variation in feed per tooth and cutting speed, is investigated. Multiple hole-drilling measurements within one sample and on different samples, machined with the same parameter set, were part of the investigations. Besides, the effect of two different clamping strategies on the MIRS was investigated. The results show that an overall repeatability for MIRS is given for stable machining (between 16 and 34% repeatability standard deviation of maximum normal MIRS), whereas instable machining, detected by vibrations in the force signal, has worse repeatability (54%) independent of the used clamping strategy. Further experiments, where a 1-mm-thick wafer was removed at the milled surface, show the connection between MIRS and their distortion. A numerical stress analysis reveals that the measured stress data is consistent with machining-induced distortion across and within different machining modes. It was found that more and/or deeper MIRS cause more distortion.

Technical note: Continuous fluorescence-based monitoring of seawater pH in situ

Electrical conductivity (salinity), temperature and fluorescence-based measurements of pH were employed to examine diel fluctuations in seawater carbonate chemistry of surface waters in Sydney Harbour over two multiple-day periods. A proof-of-concept device employing the fluorescence-based technique provided a useful time series for pH. Alkalinity with pH and temperature were used to calculate the degree of calcite and aragonite saturation (ΩCa and ΩAr, respectively). Alkalinity was determined from a published alkalinity–salinity relationship. The fluctuations observed in pH over intervals of minutes to hours could be distinguished from background noise. While the stated phase angle resolution of the lifetime fluorometer translated into pH units was ±0.0028 pH units, the repeatability standard deviation of calculated pH was 0.007 to 0.009. Diel variability in pH, ΩAr and ΩCa showed a clear pattern that appeared to correlate with both salinity and temperature. Drift due to photodegradation of the fluorophore was minimized by reducing exposure to ambient light. The ΩCa and ΩAr fluctuated on a daily cycle. The net result of changes in pH, salinity and temperature combined to influence seawater carbonate chemistry. The fluorescence-based pH monitoring technique is simple, provides good resolution and is unaffected by moving parts or leaching of solutions over time. The use of optics is pressure insensitive, making this approach to ocean acidification monitoring well suited to deepwater applications.

Determination of Ethanol in Kombucha, Juices, and Alcohol-Free Beer by EnzytecTMLiquid Ethanol: Single-Laboratory Validation, First Action 2017.07

EnzytecTMLiquid Ethanol is an enzymatic test for the determination of ethanol in kombucha, juices, and alcohol-free beer. The kit contains two components in a ready-to-use format. Quantification is based on the catalytic activity of alcohol dehydrogenase, which oxidizes ethanol to acetaldehyde and converts NAD+ to NADH. Measurement is performed in 3 mL cuvettes at 340 nm within 20 min. Samples with alcohol contents around 0.5% alcohol by volume need to be diluted 1:20 or 1:50 with water before measurement. Acetaldehyde interferes at concentrations higher than 3000 mg/L, whereas sulfite interferes at concentrations higher than 300 mg/L. The linear measurement range is from 0.03 up to 0.5 g/L ethanol, whereas LOD and LOQ are 1.9 and 3.3 mg/L ethanol, respectively. Kombucha with concentrations between 2.85 and 5.82 g/L showed relative repeatability standard deviation around 1%, whereas juices were below 2%. Results from a reproducibility experiment revealed that at a concentration of 0.1 g/L, the RSDR was at 2.5%, whereas at higher concentrations between 0.2 and 0.3 g/L, coefficients around 1% were obtained. Trueness was checked by using Cerilliant aqueous ethanol solutions and beer with concentration of 0.4 and 4 g/L (BCR-651 and BCR-652). Spiking of kombucha and juice samples resulted in recoveries between 95% and 104%. Acceptable stability was found for the whole test kit under accelerated conditions at 37°C for 2 weeks. The kit is also not susceptible to short freezing–thawing cycles and harsh transport conditions.

Interlaboratory study on the quantification of calcium phosphate phases by Rietveld refinement

An interlaboratory study (ILS, round robin) was conducted to assess the accuracy and precision of the phase quantification of calcium phosphate (CaP) bioceramics by X-ray diffraction (XRD) and Rietveld refinement. For that purpose, a mixture of hydroxyapatite and β-tricalcium phosphate, two CaP phases commonly used in synthetic bone graft substitutes, was prepared and sent to 12 laboratories for XRD analysis. Results from 26 different instruments were received and evaluated statistically according to ASTM E691 – 13. The statistical analysis revealed that the reproducibility standard deviation of phase quantities was approximately two times greater than the repeatability standard deviation, which is obtained by repeating the analysis on a single instrument configuration multiple times. The 95% reproducibility limit for phase quantities was R = ±1.67 wt%. The study also demonstrated that several participants overinterpreted their data in an attempt to refine crystallite sizes of the minor phase.

The ‘Horwitz ratio’—a study of the ratio between reproducibility and repeatability precisions in the analysis of foodstuffs

In the analysis of food, the ratio of reproducibility standard deviation to repeatability standard deviation is usually close to 2.0. This has implications in estimating uncertainty and detection capability.

Geological materials testing and uncertainty calculations: a simple GUM-based algorithm

We have applied a simple GUM-based procedure to estimate the uncertainties of physical and mechanical properties in geological materials. First, we define the quantity to measure and decide whether we want to work with units or relative quantities. Subsequently, we calculate the repeatability standard deviation (sr) and the standard uncertainty. If we have proficiency test data or use certified reference materials, we use them to estimate the laboratory bias, the reproducibility standard deviation (sR) and the reproducibility standard uncertainty. We also make sure that we know or have estimated the standard uncertainty of the instruments that we use in the measurements. The latter is typically taken from the instrument calibration or precision statement. We estimate the standard uncertainty of the reference materials and the standard uncertainty of the laboratory bias. The final two steps include the calculation of (1) the laboratory standard uncertainty uncorrected for bias and corrected for bias, and (2) the laboratory expanded uncertainty at the 95% confidence limit.

Research on the Detection Method of Emulsified Oil in Condensed Water

Emulsified oil is one of the main pollutants in condensed water. At present, the difficulties in demulsification of emulsified oil and dephenolization of petroleum ether are the main challenges in quantitative determination of emulsified oil in water by UV spectrophotometry. In this paper, second derivative ultraviolet spectrophotometry and demulsification with NaCl and ultrasonic were adopted to eliminate the disturbance of petroleum ether and avoid dephenolization process. Results show that the linear range of the standard oil is from 0 to 30mg/L, the recovery lies between 90.4%-101.6%, the relative errors are no more than 3%, the coefficient of variation are no more than 1.4%, and the repeatability standard deviation is only 0.1366. These results indicate that the emulsified oil detection method established has such advantages as high sensitivity, little interference, simple determination procedure, and accurate and reliable measuring result.

A Simple Mathematical Standardized Measurement of Acetabulum Anteversion after Total Hip Arthroplasty

We invented a standardization method to measure the cup's anteversion after total hip arthroplasty without the influence of patient's position. We measured 68 radiographs of 10 patients after total hip replacement (THR) and calculated the error of each measurement, defined as the difference with the average of the same measuring method on the same patient. We also calculated the repeatability standard deviation (RSD) of each method according to the American Society for Testing and Materials, ASTM E691.Mean absolute inter-examination angle error, defined as the average of the absolute deviations, was 0.75° for standardized anteversion (range 0.03–2.51°), as compared with those without standardization, 2.30° (range 0.04–13.04°). The inter-examination measurement reliability (precision), defined as one RSD, was 0.99° for standardized anteversion, as compared with those without standarization, 3.50°. There is no difference between patients four and five without (p = 0.097). There is a significant difference with standardization (p < 0.0001).Our study demonstrated that this mathematical method is a precise tool to measure the anteversion of the acetabular cup. We hope that it can be used widely in the future.

Liquid Chromatographic Determination of Maleic Hydrazide in Technical and Formulated Products: Collaborative Study

Fourteen collaborating laboratories assayed maleic hydrazide (MH), 6-hydroxypyridazin-3(2H)-one, in technical and formulated products by reversed-phase liquid chromatography (LC) with sulfanilic acid as an internal standard. The active MH in the samples (6 lots) ranged from 16% (expressed as the potassium salt) to 98% (MH in the technical). A small amount of 1 M KOH was added to the technical MH and analytical standards to create the potassium salt of the analyte which is soluble in water. Test samples and standards were extracted with water containing the internal standard before analysis by LC on a C8 column with an ion-pairing eluting solution and UV detection at 254 nm. The concentration of MH was calculated by comparing the peak area response ratios of the analyte and the internal standard with those in the analytical standard solution. Eleven laboratories weighed each test sample twice with single analysis. Three laboratories weighed each sample once and made duplicate injections on the LC system. The data were analyzed using the 11 laboratories' results. A second data analysis was done including all laboratory results using a Youden pair approach, selecting one of 2 duplicate assay values randomly for each laboratory and sample. In the first data analysis, the repeatability standard deviation ranged from 0.07 to 1.39%; reproducibility standard deviation ranged from 0.22 to 1.39%. In the second data analysis (using all laboratory data), repeatability standard deviation ranged from 0.09 to 0.86%; reproducibility standard deviation ranged from 0.22 to 1.31%.