Strength Testing Of Materials Research Articles

Influence of measurement uncertainties on the determination of the Weibull distribution

Abstract The influence of measurement uncertainties (MU) on the determination of the parameters of a distribution function has been analyzed using a Monte Carlo simulation technique on the example of the Weibull distribution, which describes the strength of brittle materials. It is shown that in the parameter range which is relevant for strength testing of brittle materials (e.g. ceramics) very high precision measurements are necessary if the Weibull modulus of the parent distribution is m ≥ 20. In that case the MU should be lower than ±2% of the measured value to obtain the same confidence level compared to the ideal case (MU = 0). Otherwise a significant underestimation of m becomes very probable. However, if m ≤ 10, even relatively large MU (up to ±10%) are tolerable. In summary, the precision of the measurements is acceptable as long as the width of the error distribution be much smaller than the width of the parent distribution.

Digital control systems based on Matlab/Simulink software for strength machines

This paper presents the stands for strength tests of materials and structures with digital control systems, designed and built at the Department of Mechanics and Machine Design, Opole University of Technology. The authors described electrohydraulic strength stands for tests under uniaxial tension – compression, biaxial tension – compression of cruciform specimens, and electromechanical stands for tests under cyclic bending and torsion with phase shift, and under polyharmonic bending with torsion. Fatigue tests which could be performed on these stands as well as algorithms of controllers were presented.

Production of Brick Materials from Municipal Solid Waste Ash

A lot of research is currently being done recycling, into how to reuse the waste we produce in our daily lives. This paper presents some of the results from a continuous study of recycling municipal solid waste ash (MSW-ash) into brick materials. In present study, the mixture of municipal solid waste ash and clay are used to make standard bricks fired at 900?C & 950?C. Physical characteristics including density, firing shrinkage, compressive strength and water absorption test of brick materials are reported and discussed. The results of test indicated that the municipal solid waste ash proportion and firing temperature were the two key factors determining the quality of bricks.

Test on Grouting Reinforcing Technique of Bridge Abutment Bump in Express Way

For the bridge abutment bump of express way in operation, through physical simulation experiment on the bridge-head settlement were studied to obtain the general rules of bridge-head settlement as well as the effects and parameters while grouting below the bridge-head tie-board. Grouting reinforcing method was applied to the Ning-Su-Xu West Wei River Highway Bridge; deal with the problem of bridge abutment bump. Through slurry material strength test, drill core sampling method and ground penetrating radar detect effects of grouting. Experimental results show that: By the grouting treatment below the bridge-head tie-board, which take the empty area to be filled with slurry material and make it dense, forming a whole curtain, and the density and integrity of the padding were enhanced, so, strengthening effect is very good. The practice of grouting reinforcing proves that the technique is low-cost, short construction period, and good results. So it is especially true of treating for the abutment bump of express way in operation.

Device for long-term strength testing of unidirectional polymer composite materials

An experimental device is described for testing the long-term strength of polymer composite materials. The model used is a specimen of microplastic, loaded to failure by means of a hydraulic cylinder. The case of simple tensile static loading is considered.

Strength by atomic force microscopy (AFM): Molecular dynamics of water layer squeezing on magnesium oxide

Localised strength testing of materials is often carried out in an atomic force microscope (AFM), as foreseen by Kelly in his book Strong Solids (Clarendon Press, Oxford, 1966). During AFM indentation experiments, contamination can strongly influence the observed strength and theoretical interpretation of the results is a major problem. Here, we use molecular dynamics computer modelling to describe the contact of NaCl and MgO crystal probes onto surfaces, comparable to an AFM experiment. Clean NaCl gave elastic, brittle behaviour in contact simulations at 300 K, whereas MgO was more plastic, leading to increased toughness. This paper also considers the strength of an oxide substrate contaminated by water molecules and tested by indentation with a pyramidal probe of oxide crystal. Recent theory on the effect of liquid contaminant layers on surface strength has been mainly focussed on Lennard Jones (LJ) molecules with some studies on alcohols and water, described by molecular dynamics, which allows the molecules to be squeezed out as the crystal lattice is deformed. In this work, we have focused on water by studying the forces between a magnesium oxide (MgO) atomic force microscope (AFM) probe and an MgO slab. Force versus separation has been plotted as the AFM probe was moved towards and away from the substrate. Simulation results showed that the water layers could be removed in steps, giving up to four force peaks. The last monolayer of water could not be squeezed out, even at pressures where MgO deformed plastically. Interestingly, with water present, strength was reduced, but more in tensile than compressive measurements. In conclusion, water contaminating the oxide surface in AFM strength testing is structured. Water layer squeezing removal can be predicted by molecular modelling, which may be verified by AFM experiments to show that water can influence the strength of perfect crystals at the nanometre scale.

Uniaxial compaction behaviour and elasticity of cohesive powders

The compression and compaction behaviour of bentonite, limestone and microcrystalline cellulose (MCC) — three cohesive powders widely used in industry were studied. Uniaxial compression was performed in a cylindrical die, 40 mm in diameter and 70 mm high, for three selected cohesive powder samples. The initial density, instantaneous density and tablet density were determined. The influence of maximum pressure and deformation rate was examined. The secant modulus of elasticity E sec was calculated as a function of deformation rate v, maximum pressure p and powder sample. After compaction experiments in hydraulic press at three pressures – p = 30, 45 and 60 MPa – and two different deformation rates, the strength of the produced tablets was examined in a material strength testing machine. From uniaxial compression tests performed on the universal testing machine for loading and unloading, the modulus of elasticity E was calculated on the basis of the first linear phase of unloading. The total elastic recovery of tablets was also obtained.

An improved collagen scaffold for skeletal regeneration

Bone repair and regeneration is one of the most extensively studied areas in the field of tissue engineering. All of the current tissue engineering approaches to create bone focus on intramembranous ossification, ignoring the other mechanism of bone formation, endochondral ossification. We propose to create a transient cartilage template in vitro, which could serve as an intermediate for bone formation by the endochondral mechanism once implanted in vivo. The goals of the study are (1) to prepare and characterize type I collagen sponges as a scaffold for the cartilage template, and (2) to establish a method of culturing chondrocytes in type I collagen sponges and induce cell maturation. Collagen sponges were generated from a 1% solution of type I collagen using a freeze/dry technique followed by UV light crosslinking. Chondrocytes isolated from two locations in chick embryo sterna were cultured in these sponges and treated with retinoic acid to induce chondrocyte maturation and extracellular matrix deposition. Material strength testing as well as microscopic and biochemical analyzes were conducted to evaluate the properties of sponges and cell behavior during the culture period. We found that our collagen sponges presented improved stiffness and supported chondrocyte attachment and proliferation. Cells underwent maturation, depositing an abundant extracellular matrix throughout the scaffold, expressing high levels of type X collagen, type I collagen and alkaline phosphatase. These results demonstrate that we have created a transient cartilage template with potential to direct endochondral bone formation after implantation.

Relationship between bond strength tests and other in vitro phenomena

ObjectivesThe objective of this manuscript is to outline the relationship between bond strength tests of adhesive materials and other in vitro phenomena by reviewing the literature generated over the thirty years. MethodsInformation was gathered from nearly 30 published articles appearing in dental literature. Studies were predominantly identified through a search of the PubMED database with a few additional studies published in Japanese domestic journals. ResultsStudies were included that provided evidence for the relationship between results of evaluations of the bond strengths and other in vitro phenomena such as micro-leakage, nanoleakage, structural of bonding interface and mechanical properties of bonding interface. An attempt was made to select articles that spanned the timeframe from approximately 1980 to today to try to ensure that the classic literature as well as the latest information was included. ConclusionsPrevious studies have indicated bond strength did not correlate with the results of micro-leakage tests nor gap formation at the cavity margin. The nanoleakage test and morphological and chemical characteristics of the bonding interface had potential to predict the dentin bond durability. SignificanceBond strength test results and other in vitro phenomena was not evenly correlated. According to the development of the materials, the most appropriate bond test and analysis of the in vitro phenomena should be also developed.

Material Strength Considerations in Dimension Stone Anchorage Design

Abstract One of the most important aspects of designing dimension stone cladding involves determining the configuration, size, and spacing of the anchorages that will affix the stone panels to the underlying building substrate. Information from many sources, including material strength testing, anchorage strength testing, and knowledge of the stress states created within stone cladding panels by loaded anchorages, is crucial to this process. In this paper, relationships are examined between material strength, anchorage strength, and induced stress states for four common anchorage configurations: edge dowels, Type 31 back anchors, and edge kerfs with strap and split-tail anchors. For each of these four anchor types, the relevant material and anchorage strength test data obtained for a medium-grained granite, in conjunction with finite element computer analyses of the stress states induced in the stone panels by the anchors and within the material strength test specimens, are presented. Material strength test configurations evaluated include ASTM C 880 Standard Test Method for Flexural Strength of Dimension Stone, ASTM C 99 Standard Test Method for Modulus of Rupture of Dimension Stone, and a proposed test for punching shear currently under consideration by ASTM Subcommittee C18.01. All anchorage strength tests were performed in accordance with ASTM C 1354 Standard Test Method for Strength of Individual Stone Anchorages in Dimension Stone.

The ball on three balls test—Strength and failure analysis of different materials

The ball on three balls (B3B) test is a new method for biaxial strength testing of brittle materials. A detailed analysis of the stress field in the specimens and of possible measuring errors has been made recently. The B3B-testing method has several advantages compared to common three- or four-point bending tests: for example, the edges of the specimen have no influence on the testing results, small geometrical inaccuracies of the specimens or of the test jig have only a little effect on the maximum tensile stress and friction is of minor significance. Therefore the B3B-test seems to be suitable for miniaturisation. In this paper the practical applicability of the B3B-test is investigated by measuring the strength of three ceramic materials having a low (electro ceramics), an intermediate (alumina) and a high (silicon nitride) strength. Specimens of different size (the smallest specimens had a volume of less than 1 mm 3) with polished or with as-sintered surface were tested. The results are compared with bending test results. In total more than 600 strength tests were performed. A pronounced size effect on strength could be observed, which is discussed in the framework of fracture statistics (Weibull theory). In summary the B3B-test has been proven to be a cheap and easy new testing method, which can be used to determine the biaxial strength of brittle materials and which is particularly well suited for the testing of very small specimen.

Fuzzy transition probability: a new method for monitoring progressive faults. Part 1: the theory

This paper presents a new method for condition monitoring, especially for monitoring progressive faults such as wear and fatigue. Based on the literature survey, the existing condition monitoring methods are based on either probability or fuzzy logic. The new method, called the fuzzy transition probability (FTP), combines the transition probability (Markov process) as well as the fuzzy set. From a theoretical point of view, the new method uses the available information from the training samples to the maximum extent (finding both the transition probability and the fuzzy membership) and hence, is more effective than the existing methods. This paper is the first part of a two-part paper. It presents the basic theory and shows how to compute the transition probability from the available training samples step by step. A simple demonstration example is also included. The second part of the paper presents two practical applications: one is material tensile strength testing and the other is tool condition monitoring in boring. Based on the testing results, the new method outperforms the popular artificial neural networks. Future research and applications are also discussed.

The ball on three balls test for strength testing of brittle discs: Part II: analysis of possible errors in the strength determination

Biaxial strength testing of brittle materials using the ball on three balls test (B3B test) is a useful tool for direct strength testing of disc specimens offering some advantages compared with the testing of bended beams: there are less problems with the alignment of the specimens in the fixture, in many cases the production of the specimens is easier, the area of maximum tensile stress amplitudes is far from the edges of the specimen (were often machining defects exist) and the testing procedure can easier be miniaturised. In a preceding paper, a proposal for a suitable testing set up was made, the stress fields in the disc specimens were analysed and first testing results were reported. A simple solution for the maximum tensile stress amplitude in the discs was given for a range of parameters concerning the geometry of the specimen, the supporting situation during the test and the material properties. In this paper, possible sources for deviations of this stress from the reported idealised solution (which would result in measuring errors) are discussed. For example, the not accounted influence of friction forces between the disc and the support balls, the influence of a possible buckling of the disc and the influence of geometric inaccuracies are analysed. It is shown, that the thickness of the disc is the most sensitive parameter determining the maximum tensile stress. Therefore it has to be determined with high accuracy.

A three-parameter Weibull-like fitting function for flip-chip die strength data

Die cracking in the assembly and reliability testing of flip-chip (FC) packages is often a major concern. A widely used die strength test is the so-called the four-point bending (4PB) test. In the 4PB test, the die is under pure bending and the strength of the die is determined by its breaking tensile stress. Although the 4PB test has been widely used, a well-established relation between the 4PB result and the die breaking in FC package has not been reported. This paper discusses the relation from a probabilistic mechanics point of view. The theory considers the following issues in the material strength test and the application loading conditions: (1) the die top in the 4PB test is under uniaxial tensile stress and the die in FC package is under multi-axial stress; (2) the 4PB test only puts part of the die top under tension and the die top in FC plastic package has almost 100% of the die top area under tension; (3) the die stress in the 4PB and in the package has a different distributions which contribute differently to die cracking. Weibull distribution will be used to analysis the 4PB test data. A three-parameter Weibull distribution fitting procedure will be presented. The function form of the cumulative density function of Weibull distribution is specially modified to take the above three issues into consideration and reflect the stress distribution difference between the test and application. The three-parameter Weibull fitting is compared to a two-parameter fitting. It turns out that some systems need three-parameter fitting and some other systems only need the two-parameter fitting. For systems need three-parameter fitting, a two-parameter fitting will be too conservative in design.

The ball on three balls test for strength testing of brittle discs: stress distribution in the disc

Biaxial strength testing of brittle materials is claimed to have some benefits compared to uniaxial testing, e.g. the much simpler specimen preparation, the avoiding of tensile loaded edges, the similarity of the stress state to those from typical loading (e.g. during a thermal shock loading) and the fact, that biaxial stress states are more revealing of defects than uniaxial stress states. The experience of the past showed, that biaxial strength testing has its own problems, to avoid these led to the development of several variants. One of these variants, the ball on three balls test, seems to be extremely simple: a disc is supported by three balls and then axially loaded from the opposite side via a fourth ball. In this system small deviations from the requested geometry, especially some out of flatness of the disc, are mentioned to be tolerable, but the threefold bending symmetry makes an exact analytical assessment of the stress state in the loaded disc extremely difficult. A numerical approach has yet not been performed. In this paper a FE analysis of the stress state in a ball on three balls tested disc is performed. The stress field scales with the maximum principle stress, which occurs in the centre of the tensile surface. For this stress an analytical approximation (which has been fitted to the numerical results) is given, which accounts for the influence of all relevant geometrical and material parameters. The investigated range of parameters considers the values typical for testing of brittle materials.

Mechanical response of a water-saturated core sample under opposite diametrical loadings

By use of the theory of poroelasticity, the analytical solutions were obtained for mechanical responses of a water-saturated core sample subjected to opposite diametrical loadings that vary like a step function of time (Problem I) and a linearly increasing function of time (Problem II). These loadings correspond to elastic moduli tests (by Hondros) and indirect tensile strength tests (the Brazilian tests) of dry brittle materials, respectively. The analysis showed how the diffusion of pore fluid affects these tests, if the tests are carried out for fluid-saturated samples. Furthermore, the accuracy of the Stehfest numerical Laplace inversion was checked based on the analysis. In addition, a method of determining poroelastic moduli was proposed.

On the Unification of Material Strength Testing for MEMS Applications

AbstractIn MEMS, the geometry and applied loads between strength testing coupon and structures for design are usually different and the strength data cannot be directly applied without modification for designing brittle MEMS structures. In this paper, a method based on equal failure probability is proposed to find the equivalent strength for design by scaling the test strength with a parameter called stress ratio. By the same approach, it is also possible to correlate MEMS material strength data obtained by different testing schemes.

Mechanical strength testing of stalk materials and compacting energy evaluation

The great potential of cereal lignocelluloses for use as energy or as an industrial raw material source determines the necessity to investigate the mechanical properties of stalks, as the main parts of any herbaceous material. Annual world production of cereal straw is approximately of the same amount (around 2 billion tons) as wood material production. Latvia as a country with more than 2000 lakes has wide areas, covered with reeds, which are also an important stalk material resource. Stalk cross section and structural studies show that it is a complicated structure. Special test piece preparation and clamping methods, measuring devices, testing procedure for stalk material strength testing have been worked out. Ultimate tensile (118.7±8.63 N/mm 2) and shear (8.47±0.56 N/mm 2) strength, modulus of elasticity (13.1±1.34 GPa) and shear modulus (0.643±0.043 GPa) had been experimentally determined for wheat stalks in order to find methods for mechanical conversion with minimum energy consumption. Stalk biomass compacting methods and energy requirement for that are analysed on the basis of the results from the experiments. It has been stated, that energy for wheat straw pressing (≈40 kJ/kg up to pressure 160 MPa) is one order of magnitude less than that for heating of the same mass up to 200°C in the briquetting process (≈360 kJ/kg), if solid material has to be obtained. Depending on the target goals for usage, different energy saving compacting technologies can be developed. Thus the analysis of mechanical and physical properties of the stalk materials determines the profit of biomass usage.

USING REPEATABILITY AND REPRODUCIBILITY STUDIES TO EVALUATE A DESTRUCTIVE TEST METHOD

The Elmendorf tear test is a material strength test that originated in the paper industry but is now being actively used to assess quality of fiberglass shingles. A repeatability and reproducibility (R&R) study, consisting of two separate phases because..

Experimental Assessment of Fiber-Reinforced Ceramics for Combustor Walls

Experimental and theoretical work concerning the application of ceramic components in small high-temperature gas turbines has been performed for several years. The significance of some nonoxide ceramic materials for gas turbines in particular is based on their excellent high-temperature properties. The application of ceramic materials allows an increase of the turbine inlet temperature resulting in higher efficiencies and a reduction of pollution emissions. The inherent brittleness of monolithic ceramic materials can be virtually reduced by reinforcement with ceramic fibers leading to a quasiductile behavior. Unfortunately, some problems arise due to oxidation of these composite materials in the presence of hot gas flow containing oxygen. At the Motoren und Turbinen Union, Mu¨nchen GmbH, comprehensive investigations including strength, oxidation, and thermal shock tests of several materials that seemed to be appropriate for combustor liner applications were undertaken. As a result, C/C, SiC/SiC, and two C/SiC composites coated with SiC, as oxidation protection, were chosen for examination in a gas turbine combustion chamber. To prove the suitability of these materials under real engine conditions, the fiber-reinforced flame tubes were installed in a small gas turbine operating under varying conditions. The loading of the flame tubes was characterized by wall temperature measurements. The materials showed different oxidation behavior when exposed to the hot gas flow. Inspection of the C/SiC composites revealed debonding of the coatings. The C/C and SiC/SiC materials withstood the tests with a maximum cumulated test duration of 90 h without damage.