Neural-network modeling of hot-compression test curves for calendering gasket materials

In this paper, we report on the use of neural networks (NNs) to estimate hot-compression test (HCT) curves for calendering gasket materials on the basis of their formulas. The NNs were used to demonstrate their potential during optimizing formulas for new calendering gasket materials. In the past, and to a large extent even now, the optimization of a new calendering gasket material was based on a process of trial and error, which takes a long time and is expensive because of the need for repeated experimental tests. And even after the completion of all this testing the final formula of the gasket material need not necessarily be the optimum one. We have shown that it is possible, with the assistance of a NN that was trained with appropriate data from just a small number of HCT curves, to satisfactorily investigate the valid ranges of the input data. On the basis of this investigation some valuable information was obtained that will make it easier to develop new calendering gasket materials. Using NNs, the speed of convergence to the final formula of the calendering gasket material can be much faster, because there is no need carry out many experimental HCT tests.     

Slip resistance tests for flooring: Two methods compared

In the UK the two most commonly used tests for measuring the slip resistance of flooring are the BCRA Tortus test and the RRL skid test. The corresponding safety criteria usually associated with these tests are assumed to be equivalent. Experimental results obtained on a range of flooring materials tested dry, wet and treated with two different polishes indicate that different slip resistance values are obtained from the two testers, even when the same test slider material is used in each. The relationship of these tests to service conditions remains uncertain and it follows therefore that figures quoted for coefficient of friction in BS 5395 are largely meaningless since neither the test method nor the slider material is specified.     

A new biaxial compression fixture for polymeric foams

This article presents a new biaxial compression test fixture designed for polymeric foam materials. The main advantage of the new fixture is that it is designed for uniaxial testing machines, therefore the biaxial compression measurement does not require a multiaxial test system. The geometries of the fixture and the test specimen, respectively, ensure equibiaxial loading conditions. In order to demonstrate the performance of this new device, equibiaxial measurements of a polymeric foam material are presented. The particular material under consideration is a closed-cell polyethylene foam. In addition, the relation between uniaxial compression tests and equibiaxial compression tests are presented.     

Testing requirements for hydraulic hose

The performance required of hydraulic hose used for materials handling and especially as used on earth moving vehicles is of necessity much higher than hose used on say agricultural tractors and aircraft. This extra performance is not only one of pressure needs, but also includes extremes of temperature with a fairly high level of oil resistance at high volume flows, plus flexing at very small bend radius in some instances.Compound design and the correct choice of polymer is critical under such conditions, as also is the type and combination of the reinforcement materials, which can include both textile and fine wires of high tensile strength. All of these design features in the correct permutation make the difference between a mediocre field performance and a performance that is extremely reliable, safe and satisfactory.Hose design is discussed in the context of these parameters, together with testing procedures not only in current use but future requirements under discussion and test at national and international levels. The new secant square wave pressure impulse curve is included, together with superimposed flexing of various formats, and the results and effects of such laboratory tests are critically examined in the light of the operating conditions and quality assurance.     

A new test for 'sufficient homogeneity'

Certified reference materials and materials distributed in proficiency testing need to be 'sufficiently homogeneous', that is, the variance in the mean composition of the distributed portions of the material must be negligibly small in relation to the variance of the analytical result produced when the material is in normal use. The requirement for sufficient homogeneity suggests the use of a formal test. Such tests as have been formulated rely on the duplicated analysis of the material from a number of portions, followed by analysis of variance. However, the outcome is not straightforward. If the analytical method used is very precise, then an undue proportion of the materials will be found to be significantly heterogeneous. If it is too imprecise, the test may be unable to detect heterogeneity. Moreover, the Harmonised Protocol Procedure (M. Thompson and R. Wood, Pure Appl. Chem., 1993, 65, 2123) seems to be unduly prone to the rejection of material that is in fact satisfactory. We present a simple new statistical approach that overcomes some of these problems.     

Experimental investigation on the yield loci of PA66

Compression, tensile and mixed compression/shear tests were performed on PA66 by using a universal material testing machine in order to identify the experimental yield loci of PA66. For the mixed compression/shear tests, instead of using a complex loading device, SCS (shear-compression specimens) were used to generate the additional shear stresses. Then, the mechanical behavior of materials under complex stress states can be obtained for further analysis. Results show that the experimental yield loci of PA66 obtained by the test method proposed in the present paper agree well with the theoretical model based on three stresses invariant, which indicates the reliability of the test method.     

Early recognition of oxidative degradation in polymers by chemiluminescence

Most common polymers degrade readily during normal use by reaction with oxygen. Rapid screening tests are requested by industry to characterise the oxidative stability of the materials. The chemiluminescence (CL) method, which is based on the fact that oxidation reactions of most organic materials, including polymers, are accompanied by weak emission of light, has the potential for being such a test. Selected examples of CL measurements, in a commercially available instrumentation, on different kind of materials and material formulations (as used in industrial applications) clearly indicate that the CL technique is capable of determining the relative oxidative stability of polymers at very early stages of degradation.     

Fracture energy measurements in polycarbonate and PMMA

Fracture energies in polycarbonate and PMMA were measured using different test techniques. Results from instrumented impact tests and slow three-point bend tests on Charpy specimens were compared with tensile test results on Compact Tension (CT) specimens. The Charpy specimens were provided with a blunt Charpy V (0·25 mm radius) notch and sharp (25 μm radius) notch. It is shown that impact testing of Charpy specimens with blunt notches gives values of the fracture energy which are two to six times higher than those obtained from the CT tensile tests. Only by using a sharp, 25 μm notch and performing the three-point bend test at a low rate were similar results obtained.     

Constitutive model and failure locus of a polypropylene grade used in offshore intake pipes

BorECO^®™ BA212E is a polypropylene block co-polymer which has become a common material in the manufacturing of large diameter non-pressurized gravity offshore intake pipelines. These lines are used for transportation of sea water for cooling of petrochemical process plants. The pipe sections are joined by butt heat fusion welding to create the pipeline. Recently a few premature failures of such pipelines have been reported in the field. Hence, there is a need to characterize the constitutive behavior of the pipe and weld material in order to properly design these pipes. The aim of this work is to determine the material constitutive behaviors of the pipe material and the welded joint material. Uniaxial tensile tests of both the pipe and weld joint material are conducted at various strain rates. Both the pipe and weld material show a rather high strain rate dependency, with the weld material having about half the yield strength than that of the pipe material. An analytical constitutive material model is developed for both the pipe and weld material, incorporating the effect of strain rate. The failure locus, expressed in terms of the equivalent plastic strain at failure vs. the stress triaxiality, for both materials is also determined as part of the constitutive model using notched dumbbell specimens. The constitutive model and failure loci for the pipe and weld material are implemented in a finite element model (FEM) and are validated by conducting a series of independent four-point bend experiments on both material types. The validation is carried out by comparing the FEM results of the four-point bend model with the experimental results, which show a rather good agreement.     

Ceramic microsieves: influence of perforation shape and distribution on flow resistance and membrane strength

Ceramic microsieves with slit-shaped perforations were compared to sieves with circular-shaped perforations, regarding flow resistance and membrane strength. Destructive tests show that the highest strength is obtained if the perforations are placed in a non-alternating pattern. Especially for slits, alternating patterns should be avoided as they make the structure unnecessarily flexible. The highest stress occurs at the edges of the membrane where it is attached to the support. Flexible structures bend stronger and therefore cause a higher stress at the edge, resulting in an easier rupture of the membrane. Our results show that ceramic microsieves with slits show a four to five-fold decrease in flow resistance for comparable strength related to sieves with circular pores.     

Molecular Flexibility and Bend in Semi-Rigid Liquid Crystals: Implications for the Heliconical Nematic Ground State

The N_TB phase phases possess a local helical structure with a pitch length of a few nanometers and is typically exhibited by materials consisting of two rigid mesogenic units linked by a flexible oligomethylene spacer of odd parity, giving a bent shape. We report the synthesis and characterisation of two novel dimeric liquid crystals, and perform a computational study on 10 cyanobiphenyl dimers with varying linking groups, generating a large library of conformers for each compound; this allows us to present molecular bend angles as probability weighted averages of many conformers, rather than use a single conformer. We validate conformer libraries by comparison of interproton distances with those obtained from solution-based 1D ¹H NOESY NMR, finding good agreement between experiment and computational work. Conversely, we find that using any single conformer fails to reproduce experimental interproton distances. We find the use of a single conformer significantly overestimates the molecular bend angle while also ignoring flexibility; in addition, we show that the average bend angle and flexibility are both linked to the relative stability of the N_TB phase.     

Stability Monitoring of Electrolytic Conductivity Reference Materials Under Repeated Use Conditions by the Primary Measurement Method

This work presents the results from stability studies for several electrolytic conductivity (EC) reference materials submitted to repeated use conditions, as required by the last version of the ISO 17034 standard. Eight batches of reference materials, composed of water or water/n-propanol and HCl or KCl (at different concentrations), were studied, with nominal EC values ranging from 5 to 12,825 µS·cm−1. The materials were submitted to a simulation of repeated use, with the manipulation of bottles once a week and their storage under refrigeration with air gaps inside them. They were then analyzed once a month by the EC primary measurement method. The measurement results were evaluated to check for deviations from conventional long-term stability monitoring and for variation trends using normalized error and linear regression statistical tests. The results indicated that the repeated use simulation caused deviations in the EC for the 100 and 500 µS·cm−1 reference materials and variation trends in the EC for the 5000 and 12,825 µS·cm−1 reference materials. From the results, the uncertainty related to stability monitoring under repeated use conditions was calculated for each reference material.     

Experimental approach for microscale mechanical characterization of polymeric structured materials obtained by additive manufacturing

In this paper, an original experimental method is developed for local strain characterization at the surface of additively manufactured polymeric materials. The process used herein is material extrusion. This experimental method is based on the use of microscopic speckle pattern deposited at the surface of micro single edge notched specimen (μ_SENT) made of acrylonitrile butadiene styrene (ABS). Two configurations of filament orientation were used for the specimen manufacturing. Images of the μ_SENT specimen surface were recorded during in-situ tensile test. The quantitative analysis of images was made by digital image correlation (DIC). The evolutions of the local strain heterogeneities and the crack tip are evidenced on the kinematic fields. It is shown that the crack propagates in the low resistance path which is the interface area between filaments. It is also evidenced that the intersection of perpendicular filaments in two adjacent layers blocks crack growth. The local strain evolutions at the surface of the specimen are compared to the macroscopic response of the material. The method developed herein allows the determination of the materials mechanical properties. The identification of the crack tip location using digital image correlation (DIC) and J-integral calculation lead to plot the J-R curve. The J-R curves comparison of the two specimen configurations shows that the fracture toughness is directly related to the material structure.     

Determination of non-linear dynamic properties of carbon-filled rubbers

A forced non-resonance test method is described for determining the dynamic mechanical properties of polymeric materials over wide ranges of strain and frequency. The use of this method for carrying out studies on carbon-filled rubbers is illustrated by results which demonstrate the variation of the dynamic shear modulus and damping factor of a tyre tread material with dynamic strain amplitude, frequency and temperature. Procedures are discussed for the analysis and presentation of such data.

Two methods are described for the determination of loss factor, and results from these are compared in order to assess the validity of phase angle measurements on non-linear materials.

Brief reference is made to dynamic testing under compressive and combined compression and shear modes of deformation. The prediction of performance under this combined loading situation from experimental data obtained in shear is demonstrated.     

Creatinine determination in urine from the point of view of reference values

In this paper, the creation of a certified reference material for urinary creatinine is described. We used the Jaffe method and HPLC method for establishment of the certified value. Homogeneity tests are also described. We obtained material with sufficient homogeneity, stability, and with certified value (expanded uncertainty, k=2 for CI 95%) (7.77±0.27) mmol·L⁻¹. This material was consequently used for the interlaboratory comparison (EQA Czech Republic for clinical chemistry). Twenty-nine percent of the participants obtained measurement results within the interval of the certified value ± expanded uncertainty, while 85% of the participants obtained values inside the interval of the certified value ± target measurement uncertainty. Direct use of the certified reference materials for method evaluation in EQA programs means a significant advance for monitoring and documentation traceability of results in routine measurements.     

In-house quality control material of nicarbazin and narasin in eggs: preparation and inter-laboratory evaluation

Coccidiostats are a group of pharmacologically active substances widely used in veterinary practice. Their residues are detected relatively often in poultry tissues and egg samples analyzed as part of official residue control programs in the European Union. Therefore, accuracy of quantitative results needs to be monitored through internal and external quality control studies. In addition, the use of materials containing incurred residues would be welcome to for ongoing monitoring of the method accuracy. Unfortunately, in the field of veterinary drug residues, certified reference materials are often unavailable. Therefore, in-house quality control material of incurred lyophilized eggs containing narasin and nicarbazin has been produced and characterized. The eggs originated from hens receiving feed with coccidiostat premix Maxiban were mixed to obtain presumed concentrations of residues and freeze-dried. Homogeneity of the material was verified by the duplicate analysis of ten random samples, and the results proved that the between samples variation was negligible in comparison with the method repeatability. No measurable loss of analytes was observed within 1 year; the slope of the regression line of the results of stability measurements was not significantly different from zero. The assigned values were expressed as medians of the results of inter-laboratory comparison performed in four different European laboratories; the uncertainty of the material was estimated, taken into consideration all above tests, resulting in (14.4 ± 2.53) µg/kg for nicarbazin and (7.91 ± 1.52) µg/kg for narasin.     

Influencing factors for static immersion tests of compatibility between elastomeric materials and lubricants

Material compatibility is an important factor to consider during the development of new lubricants and sealing materials. Static immersion tests provide a first idea about the compatibility between elastomeric materials and lubricants. For the same material combination, significant deviations among the test results of different laboratories have been reported. In order to identify the relevant factors affecting the results, a systematic investigation was carried out. Reproducibility tests show that the estimation of the compatibility is compromised due to the deviations that appear for the change of the mechanical properties of the considered reference elastomers. The influences of the closure of the test apparatus and the volume ratio, as well as the development of the aging process, were investigated. The results showed that, in order to differentiate between elastomer-lubricant material combinations, standard test durations of approximately 1008 h are preferred. Volume ratios of 64 and 80 and small variations of the vessel closure did not lead to significant deviations of the results. In contrast, tests with open and closed vessels showed significant deviations for the hardness and mechanical properties of the elastomeric materials.     

Trace element determination in a mussel reference material using short irradiation instrumental neutron activation analysis

The production of certified reference materials in Brazil, and the consequent availability to national end users, is an important task for the enhancement of Metrology in Chemistry status in the country, as these materials are used for method validation, equipment calibration and for establishing metrological traceability links. In this study, Instrumental Neutron Activation Analysis (INAA) was applied to the determination of bromine, chlorine, magnesium, manganese, potassium and vanadium in a mussel reference material produced at IPEN-CNEN/SP. For the determination of these elements via the comparative INAA method, the respective analytical radionuclides, ⁸⁰Br, ³⁸Cl, ²⁷Mg, ⁵⁶Mn, ⁴²K and ⁵²V, are short lived and then, short irradiations are used. Six subsamples from two bottles of the Perna perna mussel reference material were analyzed. Each subsample was simultaneously irradiated with elemental standards for 10 s at the IEA-R1 research nuclear reactor through a pneumatic transfer system. After suitable decay periods, gamma radioactivity measurements were carried out, using a hyperpure germanium detector. The accuracy of the method was checked by using the NIST SRM 1566b–“Oyster Tissue” certified reference material. The comparison of the results obtained in this study to the robust mean of the interlaboratorial collaborative trial used for the characterization of the mussel reference material was performed via z-score tests. The comparison showed that the short irradiation INAA method is suitable for the characterization of new reference materials.     

Comparative mechanical property characterization of three indirect composite resin materials compared with two direct composites

Various new indirect composite materials have been developed with required advantages. In this study three indirect composite material (Artglass, Belleglass HP, Targis) were tested for flexural strength, fracture toughness, wear resistance and hardness against Filtek P60 and Z‐100. Five specimens of each material were fabricated according to the manufacturer's directions. The flexural strength and fracture toughness was measured using the bending test. The wear test was performed to accelerated wear in a toothbrushing apparatus. Vickers hardness was measured for each of the tested materials. The statistical tests used for flexural strength, fracture toughness, wear and hardness were One‐way ANOVA and Kruskal–Wallis test. The level of statistical significance chosen was p = 0.05. Results of the study showed that Filtek P60 was superior to the other composites in all tests. Significant differences were found among the materials. The differences in flexural strength, fracture toughnes, wear and hardness may have been due to differences in chemistry or method of polymerization of the composites. Copyright © 2003 John Wiley & Sons, Ltd.     

Design of a modified three-rail shear test for shear fatigue of composites

There are various ways of determining the static in-plane shear properties of a fibre-reinforced composite. One of them is the standard three-rail shear test, as described in “ASTM D 4255/D 4255M The standard test method for in-plane shear properties of polymer matrix composite materials by the rail shear method”. This setup, however, requires drilling holes through the specimen. In this study, a new design based on friction and geometrical gripping, without the need of drilling holes through the composite specimen is presented. Quasi-static tests have been performed to assess the symmetry of the setup and the occurrence of buckling. Then, fatigue tests were done to assess the behaviour of the grips under fatigue loading conditions, yielding excellent results; the specimen fails under shear loading conditions in the loaded area. The material used to validate this setup was a carbon fabric-reinforced polyphenylene sulphide.

During fatigue, this material shows an increase in permanent deformation and a decrease in shear stiffness until a certain point in time, after which a drastic increase in deformation and temperature, higher than the softening temperature of the matrix occurs. Furthermore, the maximum value of the shear stress for fatigue with R=0 has a large influence on the fatigue lifetime.