Showing papers in "Journal of Testing and Evaluation in 2009"

Crack Size Evaluation Using Unloading Compliance in Single-Specimen Single-Edge-Notched Tension Fracture Toughness Testing

Abstract: Crack-mouth-opening displacement (CMOD) unloading compliances of single-edge-notched tension (SE(T)) specimens, both pin-loaded and clamped, have been evaluated by finite element analysis (FEA), including evaluation of the effect of rotation during testing on compliance. For pin-loaded specimens, FEA results are compared with compliance correction equations based on a rigid-body rotation model recommended by Joyce and Link. The results agree reasonably well when the load line is far from the midsection of the ligament. However, the discrepancy increases when the load line approaches the midsection of the ligament where the bending load becomes small or negligible compared with the tension component and the rigid-rotation model breaks down. For clamped SE(T) specimens, factors affecting specimen rotation, such as the ratio H/W of span between load points H to width of the specimen W, normalized crack size, a/W, and material strain hardening coefficient, N, were investigated. This work was performed for specific application to surface circumferential cracks in pipes, for which the best constraint matching has been found to occur for clamped specimens with H/W = 10. For this geometry, an equation is proposed to correct compliance for rotation and to estimate crack size from rotation-corrected CMOD compliance. Crack sizes evaluated using this equation are compared with measurements on broken specimens. Excellent agreement has been achieved for initial and final crack sizes of both plain-sided and side-grooved SE(T) specimens.

Determination of Volumetric Properties for Permeable Friction Course Mixtures

Abstract: Current hot mix asphalt (HMA) mix design procedures used to determine the optimum asphalt content (OAC) for permeable or porous friction course (PFC) mixtures are based on volumetric properties, primarily total air void (AV) content. This calculated volumetric parameter depends on the bulk specific gravity (Gmb) and the theoretical maximum specific gravity (Gmm) of the mixture, which are generally difficult to measure in a laboratory due to the high asphalt contents, high total AV contents, and the use of modified asphalts for PFC mixtures. This study evaluated two methodologies for determining Gmb (vacuum and dimensional analysis) and two methodologies for determining Gmm (measured and calculated) for use in calculations of total AV content. For the mixtures assessed in this study, originally designed with a total AV content of 20 %, the alternative methodologies studied led to total AV content values outside the design range (18 to 22 %), which implies the necessity of gradation modifications or changes in the fiber content to meet AV requirements and define an OAC. Dimensional analysis and a calculation procedure, based on values of Gmm measured in the laboratory at low asphalt contents, are recommended for determining Gmb and Gmm values, respectively. In addition, dimensional analysis is preliminarily recommended to compute the water-accessible AV content of PFC mixtures based on the assessment of two methods (vacuum and a methodology proposed for dimensional analysis) to compute this parameter. Water-accessible AV content is considered as an alternative parameter for mix design and evaluation.

Flexural Strength of Ceramic and Glass Rods

Abstract: Flexural testing is the most common method used to measure the uniaxial tensile strength of ceramics and glasses. Although standard test methods have been developed for rectangular specimens, cylindrical rod specimens may be preferred in many cases. This paper summarizes how rods have been tested in the past, identifies key experimental errors and remedies, and serves as the foundation for a new standard test method for ceramics and glasses.

Evaluation of Semicircular Bending Test for Determining Tensile Strength and Stiffness Modulus of Asphalt Mixtures

Abstract: The semicircular bending (SCB) test has been shown to possess several advantages over other tests in characterizing asphalt mixtures in previous studies. This research study evaluates the SCB test for determining the tensile strength and stiffness modulus of the paving material with numerical simulation and laboratory experimentation. An analytical model describing the tensile stress at the middle point of the lower surface of the specimen in the SCB test was developed based on the plane assumption in mechanics of materials. Analysis using the finite element method indicated that the error induced by the model was within 2 %. Laboratory experiment carried out on three types of asphalt mixtures at various temperatures showed that the strength of the material by the SCB test was nearly 50 % higher on average than that by the flexural beam bending (FBB) test due to such factors as complexities in stress and strain states as well as nonlinearity and viscoelasticity of the material. Laboratory experiment also showed that the stiffness moduli for 10–40 % of maximum load from the FBB test and from the SCB test were in a well-defined linear relationship with differences less than 10 %. In addition, based on finite element analysis, a practical approach for determining stiffness modulus of asphalt mixtures using deflection at the middle point of the lower surface of the specimen in the SCB test was established.

Effects of Various Long-Term Aging Procedures on the Rheological Properties of Laboratory Prepared Rubberized Asphalt Binders

Abstract: Rubberized asphalt has been used to improve the mechanical characteristics (e.g., rutting resistance, fatigue life, friction, and skid resistance) of hot mix asphalt mixtures. The objective of this research was to investigate the rheological characteristics of the rubberized asphalt binders after various long-term aging procedures, using the penetration index, the dynamic shear rheometer, the bending beam rheometer, and high pressure-gel permeation chromatographic testing. The experimental design included the use of three binder sources, three binder grades (PG 64-22, PG 64-22+10 %-40 ambient rubber, and PG 76-22) and three aging states, i.e., virgin, rolling thin film oven, and pressurized aged vessel [four test temperatures (65, 80, 100, and 110°C) and five aging durations (15, 20, 40, 80, and 144 h) under the pressure of 2070 kPa]. The test results show that, as expected, the use of crumb rubber can effectively improve the PG grade and aging resistance of the virgin asphalt binder. A series of rheological properties (e.g., penetration, stiffness, m-value, and percentages of large and small molecular sizes) illustrate that the PG 64-22 binder, mixed with 10 %-40 ambient rubber, yields similar or improved rheological properties in comparison with PG 76-22 using 3 % styrene-butadiene-styrene polymer after various long-term aging procedures.

Connected Air Voids Content in Permeable Friction Course Mixtures

Abstract: Current hot mix asphalt (HMA) mix design procedures used to determine the optimum asphalt content for permeable or porous friction course (PFC) mixtures are based primarily on total air void (AV) content. Durability and functionality of PFC mixtures are also related to the total AV content. However, the connected AV content (defined as the proportion of AV that form connected pathways for air and water transport through PFC mixtures) may provide more insight into the mixture structure in terms of the AV content directly associated with functionality and durability properties and constitute an alternative parameter to conduct PFC mix design and evaluation. This study evaluated two laboratory methodologies (vacuum and dimensional analysis) for determining water-accessible AV content and two types of analysis to compute interconnected AV content based on X-ray Computed Tomography (X-ray CT) and image analysis techniques. Although both the interconnected AV content and water-accessible AV content constitute determinations of connected AV content, different nomenclature was used to differentiate the origin of the calculation. Dimensional analysis with application of vacuum and X-ray CT and image analysis with inclusion of surface AV are recommended for determining water-accessible AV content and interconnected AV content, respectively. Future work should focus on investigating the use of connected AV content as an alternative parameter to integrate in mix design and laboratory and computational evaluation of PFC mixtures.

Measurement and Simulation of Thermal Stability of Poly(Lactic Acid) by Thermogravimetric Analysis

Abstract: The thermal degradation of poly(lactic acid) (PLA) biopolymer was studied as used by the thermogravimetry analyzer in a nitrogen atmosphere in the temperature range of 100–500°C. The reaction was found under these experimental conditions to be of first order with an activation energy of 94.0 and 105.3 kJ/mole and pre-exponential factor 6.43×105 and 1.91×106 1/s, respectively. Slight differences have been found in activation energy depending on the analytical methods used and reported in other previous articles. It was found that the activation energy of thermal degradation increased with increasing the molecular weight of PLA. Moreover, the behaviors involved in the thermal degradation of PLA in nitrogen atmosphere were studied by using the numerical simulation of the kinetic model to dynamical thermogravimetric data. The maximum decomposition temperature, shape index for dynamic condition and life, and degree of decomposition for the isothermal condition of thermal behavior of PLA are predicted via mathematical simulation in this study.

The Effect of Curing Regime on Pervious Concrete Abrasion Resistance

Abstract: The current method of curing pervious concrete is to cover with plastic for 7 days, although no studies have been performed to determine if that is sufficient or even required. This paper presents results of combinations of four different pervious concrete mixtures cured using six common curing methods. The surface abrasion of the concrete was tested using a rotary cutter device according to ASTM C944. The results show that the concrete abrasion resistance was improved with a majority surface-applied curing compounds; however the surfaces covered with plastic sheets produced the lowest abrasion levels. A majority of the curing regimes also produced higher flexural strength than the control concrete. There was no significant difference observed in the strength between curing under plastic sheets for 7 or 28 days. Of the surface-applied curing compounds, the best abrasion resistance and highest strength concrete was that applied with soybean oil. The best abrasion resistance and highest strength overall was the mixture containing fly ash and cured under plastic for 28 days.

Calibration Procedures for the Intelligent Asphalt Compaction Analyzer

Abstract: The intelligent asphalt compaction analyzer (IACA) is a device based on neural network technology that can measure the density of an asphalt pavement continuously in real time during its construction. It was shown during limited field trials that the IACA could, in real time, measure the density of an asphalt pavement during its construction with accuracy comparable to existing point-wise measurement technologies. In this paper, the procedure to calibrate the IACA and the validation of the performance, i.e., accuracy of density measurements, are addressed. The results demonstrate that the IACA can be used to determine the density of the asphalt mat during compaction with an accuracy needed for quality control operations in the field.

Effects of Densification on Permeable Friction Course Mixtures

Abstract: Compaction of permeable or porous friction course (PFC) mixtures is generally considered a process without major issues, and field density requirements (or corresponding total air voids [AV] content) are not currently specified for this type of hot mix asphalt. However, proper densification is one of the most important aspects to control during construction to prevent raveling, the distress most frequently reported as the cause of failure in these mixtures. This paper presents an evaluation of the effect of densification on PFC mixtures. This evaluation included both the study of the internal structure of compacted mixtures and a comparison of performance based on macroscopic response. Results from this study showed that differences encountered in the internal structure of road cores and specimens compacted using the Superpave Gyratory Compactor limit the use of these laboratory compacted specimens in durability and functionality evaluations of PFC mixtures. In addition, changes in densification, after reaching stone-on-stone contact, modified the mixture properties and performance. The magnitude of these modifications provided evidence of the ease of verifying not only stone-on-stone contact during mix design, but also of the importance of controlling the density during construction to ensure an equilibrium density that guarantees the balance between mixture durability and mixture functionality.

Reliability Life Prediction of VFD by Constant Temperature Stress Accelerated Life Tests and Maximum Likelihood Estimation

Abstract: In order to obtain the life information of vacuum fluorescent display (VFD) in a short time, four constant stress accelerated life tests (CSALT) are conducted with the cathode temperature increased. Lognormal function is applied for describing the life distribution of VFD. Assuming an Arrhenius model, the lognormal parameters are computed by using the maximum likelihood estimation. Furthermore, a self-developed software is employed in predicting the VFD life. The statistical analysis of the results indicates that the test design of CSALT is correct and feasible, that the average life of VFD is over 30,000 h, and that the life-stress relationship satisfies linear Arrhenius equation completely. The precise accelerated parameter is shown to be particularly useful to predict the VFD life within shorter time. Thus, this work provides significant guidelines to help engineers make decisions in design and manufacturing strategy from the aspect of reliability life.

Effects of Binders on Resilient Modulus of Rubberized Mixtures Containing RAP Using Artificial Neural Network Approach

Abstract: The prediction of the resilient modulus values of rubberized mixtures containing reclaimed asphalt pavement (RAP) materials involves a number of interacting factors or engineering parameters (variables) and is a very complex issue. Artificial neural networks (ANN) are useful tools in place of conventional physical models for analyzing complex relationships involving multiple variables and have been successfully used in many civil engineering applications. The objective of this study was to develop a series of ANN models to simulate the resilient modulus of rubberized mixtures (ambient and cryogenic rubbers) at 5, 25, and 40°C using seven input variables including material components such as rubber and RAP percentages as well as the rheological properties of modified binders (i.e., viscosity, G*sin δ, stiffness, and m-values). The sensitivity analysis and important index of each variable were performed in this study. The results indicated that ANN-based models are more effective than the regression models and can easily be implemented in a spreadsheet, thus making it easy to apply. In addition, the validation analysis of the models showed that ANN-based models might be used for other types of mixtures. Moreover, the results of the sensitivity analysis and important index of input variables in ANN models also indicated that the rheological properties of asphalt binders can be employed to predict the resilient modulus values effectively at various testing temperatures. The validation of the model also illustrates that the developed ANN can be used to predict the resilient modulus values from other research projects.

Yield Strength Evaluation by Small-Punch Test

Abstract: Because of the mechanical property degradation experienced by the nuclear power plant components, it is important to evaluate the evolution of the mechanical properties during service, such as the yield strength. A lack of materials available from nuclear power plants has led to the development of more and more small-sized specimen tests such as the small-punch test that has the advantage of using very small amounts of material with very simple working conditions (machining and test). In this study, we will present a new method for the yield strength estimation. This method is based on the elastic deformation energy method and is compared with the current methods which include the “two tangents” method and the offset method. This new method consists of the determination of the yield strength by measuring the energy beneath the load-displacement curve in the elastic deformation domain. The elastic deformation domain is defined by measuring the elastic reverse displacement during an unloading phase. Subsequently, the elastic displacement reverse is applied at the beginning of the load-displacement curve. Good agreement has been found between the elastic deformation energy and the square of the tensile yield strength. This method allows a better evaluation of the tensile yield strength and with a reduced scatter compared to the current conventional methods.

A Critical Review of the Methodologies Employed for Determination of Tensile Strength of Fine-Grained Soils

Abstract: Tensile strength of fine-grained soils plays a significant role in assessing their cracking characteristics, which govern their suitabil- ity as a construction material for landfill liners and covers, earthen dams, embankments, and pavements. As such, determination of this property of these soils becomes essential. In this context, various experimental techniques that have been developed by earlier researchers to determine tensile strength of fine-grained soils are worth appreciating. Based on the experimental results obtained from these studies, several empirical relationships have been proposed. However, these relationships relate tensile strength of the soil with a single parameter (i.e., suction, plasticity index, liquid limit, CEC, clay content, or water content).This necessitates: (a) critical evaluation of such relationships, and (b) development of a generalized relationship that employs multiple soil properties. With this in view, investigations were carried out on some fine-grained soils and their tensile strength was determined by conducting undrained triaxial tests and suction measurements. Details of the methodologies adopted are presented in this paper and efforts have been made to achieve the two objectives mentioned above.

Method of Compaction has Significant Effects on Stress-Strain Behavior of Hydraulic Asphalt Concrete

Abstract: Four different laboratory compaction methods, i.e., the Marshall, vibration, static, and gyratory methods, were used to study the effects of type of compaction method on the triaxial stress-strain behavior of asphalt concrete. The behavior was compared to that of asphalt concrete compacted in the field by a vibratory roller. Although the asphalt concrete specimens were all made of the same mix and compacted to approximately the same density (air voids), the resulting stress-strain curves were very different. The secant modulus up to 1 % axial strain for the gyratory compacted specimens was six times that of the field compacted specimen, and the axial strain of the field specimen at failure was six times that of the gyratory specimen. The reason is that, although the asphalt concrete density is the same for the different specimens, the aggregate particle arrangement and interlocking (skeleton structure) after compaction are very dependent upon the method of compaction used. For field quality control, common practice is to compare the behavior of field compacted specimens to specifications based on laboratory specimens. Therefore, it is important to use laboratory compaction methods that yield specimens with behavior similar to that resulting from roller compaction in the field. Two such methods are proposed, a modified Marshall method and a special compaction method.

An Efficient Inverse Method for Identification of the Location and Time History of an Elastic Impact Load

Abstract: An inverse method to identify the location and time history of a single elastic impact load based on the time dependent structural responses is presented. At first, the unknown impact location is found through an inverse analysis without any information about the time history of the load. Two different methods are presented for the location identification. In both methods, an objective function expressing relationship between pairs of structural responses is minimized to find the optimal impact location. In the first method, the steepest descent technique is used to find the impact location precisely. In the second method, a zero-order search technique is developed for fast, but a little less accurate, identification of the impact location. After determining the location, the time dependent value of the impact load is reconstructed using the least-squares method. In-plane strain and its time integrals at sampling points are used to find the location and history of the impact load. In case of high strain fluctuation, time integration of strain removes fluctuations without introducing any additional error. This significantly simplifies the time history determination of the impact load. Two examples are presented to show the validity and effectiveness of the proposed method.

Significance Evaluation of Material and Additive Factors Influencing Moisture Susceptibility of Asphalt Mixtures

Abstract: Many factors have been identified to have influences on the moisture susceptibility of asphalt mixtures. This research study attempts to evaluate such factors as binder type, aggregate type, mixture type, additive usage, additive type, additive application approach, and additive organic nature. Tensile strength ratio (TSR) was tested on twelve asphalt mixtures of three types, with two binders and three aggregates, and with improving measures as three antistripping additives and two application approaches. Multiple variable statistical analyses were employed on the TSR data in assessing the significance of the factor. Test results and data analyses indicate that the extent of the influence varies considerably from one factor to another. The styrene-butadiene-styrene modified binder is superior to neat petroleum binder for producing asphalt mixtures subject to damp conditions. Granite, basalt, and limestone aggregates make asphalt mixtures that are least, in-between, and most resistant to moisture damage, respectively. Compared with dense graded asphalt concrete (AC) and stone matrix asphalt (SMA) mixtures, porous asphalt macadam (AM) mixtures are more prone to stripping. The usage of inorganic hydrated lime and Portland cement, and organic amine antistripping agent can substantially improve the moisture susceptibility of asphalt mixtures; the wet approach for applying the inorganic additives can result in better effects than the dry approach. Different additives show little difference in improving effects with mixed trends and the inorganic and organic additives are similar in performance with variations that are immaterial.

Estimation of Subgrade Soils Resilient Modulus from in-situ Devices Test Results

Abstract: Field and laboratory testing programs were conducted to develop resilient modulus prediction models for application in the design and evaluation procedures of pavement structures. The field testing program included conducting several in-situ tests such as Geogauge, Light Falling Weight Deflectometer, and Dynamic Cone Penetrometer (DCP). The laboratory program consisted of performing repeated load triaxial resilient modulus tests, physical properties, and compaction tests on soil samples obtained from tested sections. A total of four subgrade soil types at different moisture-dry unit weight levels were considered. Comprehensive statistical analyses were conducted on the field and laboratory test results. Two sets of models were developed. The first set (direct model) directly relates the laboratory measured resilient modulus values with the results of each of the three in-situ devices, whereas the second set (soil property model) incorporates soil properties in addition to the results of each of the three in-situ devices. A good agreement was observed between the predicted and measured values of the resilient modulus. Furthermore, the results showed that the resilient modulus prediction was enhanced when the soil properties were included as variables within the models. Among the models developed, the DCP-soil property model had the best prediction of resilient modulus followed by the DCP-direct model. The effectiveness of the DCP models were further evaluated during a forensic analysis of pavement section failure in a highway within Louisiana.

The Influence of Aggregate Interaction and Aging Procedure on Bitumen Aging

Abstract: Bitumen, like many other organic substances, is affected by the presence of oxygen, ultraviolet radiation, and by changes in temperature. These external influences result in the phenomenon known as “aging” and cause changes in the chemical composition and therefore the rheological and mechanical properties of the bitumen. Aging is primarily associated with the loss of volatile components and oxidation of the bitumen during asphalt mixture production (short-term aging) and progressive oxidation of the in-place material in the field (long-term aging). Both factors cause an increase in viscosity (or stiffness) of the bitumen and consequential stiffening of the asphalt mixture. Aging at moderate levels is generally accepted and can even enhance performance, but at significant levels results in embrittlement of the bitumen, significantly affecting its adhesive characteristics and usually resulting in reduced cracking resistance of the asphalt mixture under repeated loading. It has long been recognized that the characteristics of bitumens are affected by the mineral aggregate with which they come into contact and that age hardening is influenced by both the bitumen and the mineral aggregate as reported by Bell and Sosnovske in 1994. This paper investigates the influence of aggregate type and aging procedure on the rheological and chemical fractional properties of aged bitumen. Asphalt mixtures comprising limestone or granite aggregate have been artificially aged in the laboratory and the rheological properties and chemical composition of the recovered bitumen from the mixtures determined after different durations of aging. In addition, the influence of bulk aging versus thin film aging has been assessed on the same bitumen aged in the presence of aggregate.

Performance of Composite Modified Asphalt with Trinidad Lake Asphalt used as Waterproofing Material for Bridge Deck Pavement

Abstract: Performance of composite modified asphalt with Trinidad Lake Asphalt (TLA) used as waterproofing material for bridge deck pavement was studied through the shear test, pull-out test, and water permeability test. The results showed that shear strength at 20°C of composite modified asphalt with TLA was affected by the material dosage and the optimum dosage was 1.2 kg/m2. Shear strength at 20°C of composite modified asphalt with TLA increased with the increase of TLA content and then decreased with the further increase of TLA content. However, the shear strength at 50°C shows different results. Based on shear strength at 20°C, the optimum TLA content was 20 % by total weight of composite modified asphalt. Bond strength at 20°C of composite modified asphalt with TLA was very close to that of styrene-butadiene-styrene (SBS) modified asphalt but the bond strength at 50°C of composite-modified asphalt with TLA was 47 % higher than that of SBS modified asphalt. Both composite modified asphalts with TLA and with SBS modified asphalt met the impermeability requirement. Composite modified asphalt with TLA could be used as waterproofing material for bridge deck pavement for better performance.

Revised Incremental J -Integral Equations for ASTM E1820 Using the Crack Mouth Opening Displacement

Abstract: The incremental J-integral equations used in ASTM E1820 were developed utilizing the work input to the test specimen, and utilize the load versus load-point/line displacement (LLD) data obtained from the fracture test. The analysis of Ernst [Fracture Machanics: Thirteenth Conference, ASTM STP 743] was then used to obtain crack growth corrected estimates of the J-integral as needed for an accurate J-R curve evaluation. For the compact type specimens, the crack mouth opening displacement (CMOD) gage was moved to the load line so that an adequate estimate of LLD could be obtained from the clip gage and utilized for compliance-based crack extension and incremental J-integral estimates. For the single edge-notched bend [SE(B)] specimens, however, it has been necessary to measure both CMOD for compliance-based crack length estimates and LLD for the crack growth corrected J-integral calculations. Additional experimental complexity and expense are thus added. ASTM E1820 includes a “basic” procedure which allows evaluating the J-integral using CMOD without crack growth corrections if the result is used only for evaluation of initiation toughness. Recently, Annex A16 based on work of Wallin and Laukkanen [Engineering Fracture Mechanics, Vol. 71, 2004, pp. 1601–1614] has been added to ASTM E1820 that presents a multiple-step procedure to obtain a crack growth corrected J-R curve from the basic method data. A more direct approach was proposed recently by Zhu [Journal of ASTM International, Vol. 5, No. 5, 2008, paper ID: JAI 101532] using an incremental procedure to obtain the desired, crack growth corrected J-R curve from the CMOD data of SE(B) specimens with two geometry factors ηCMOD and γCMOD similar to the parameters presently used in the existing LLD-based J-integral analysis. Using fracture toughness test data for SE(B) specimens, detailed comparisons and discussions are made between the proposed method and the ASTM E1820 CMOD methods in determination of J-R curves for HY80 steels. As the basis of comparison, the “accurate” solutions obtained from the standard LLD-based incremental J-integral method are provided for all specimens considered. The difference between the CMOD and LLD methods are then quantified. The results show that the proposed CMOD incremental J-integral equations are simple and effective, and thus are recommended here for use in ASTM E1820 for testing J-R curves and for reducing test costs and complexity.

Sensitivity of Road Unevenness Indicators to Road Waviness

Abstract: Currently used single-number indicators of longitudinal road unevenness suffer from their nonuniqueness due to the ignorance of waviness, which is the measure of wavelength distribution in road profile spectrum. Six single-number unevenness indicators were taken into account, viz. unevenness index, straightedge index, International Roughness Index for two velocities (80 and 120 km/h), spectral evenness index, and equivalent unevenness index. A simulation study was conducted, in which the waviness varied in the range from w = 1.5 to 3.5. In addition two representative road vehicles, a personal car and a truck, and three different travel speeds v = 60, 90, and 120 km/h were considered. The ranges of ten different vibration responses were established and related to the reference. The lowest sensitivity to varying waviness has been found for an equivalent unevenness index, which is the standard unevenness index multiplied by a correction factor accounting for the influence of waviness, and for IRI estimated for v = 120 km/h.

Ductile Damage Analysis for Small Punch Specimens of Type 304 Stainless Steel Based on GTN Model

Abstract: Based on small punch (SP) tests on Type 304 stainless steel at room temperature, a finite element (FE) model with Gurson-Tvergaard-Needleman (GTN) constitutive equations was established to analyze the ductile damage in SP specimens. Influences of the friction coefficient between SP specimen and steel ball and element size to the FE results were discussed. The evolution of void volume fraction (VVF) with time along different paths and the relation between VVF and equivalent plastic strain (PEEQ) under constant punching velocity were analyzed further by using the FE model. Good agreements between experimental results and simulation data were proved by load-displacement curves and failure locations. The numerical results show that initial crack occurs at the bottom surface about 0.86 mm away from the centre and damage localization phenomenon is extraordinarily severe in the SP specimen, and PEEQ has great effect on the evolutional rate of VVF.

Influence Treatment in Laboratory of Stone Surface on the Surface Roughness

Abstract: Adhesion properties of asphalt mixtures are very important. Especially for porous asphalt adhesion problems are immediately a possible cause of low durability. At Delft University of Technology, research on the adhesive zone between the bituminous mortar and the stone is in progress. Small test specimens were produced and the aggregates received all kinds of treatments (sawing, coring, sandblasting, etc). An important question is if these test specimens are representative for the actual surfaces of the aggregates in the mixture. In this paper the possible influence on bitumen-aggregate adhesion of different stone surface characteristics is discussed. For this purpose, roughness tests are conducted on treated aggregate surfaces for columns used in the laboratory tests and the real stone particles as used in mixtures. Roughness (stereo-, confocal, and electron microscope), specific surface area (stereo- and confocal microscope), and surface free energy (sessile drop) are determined. It is concluded that sawing and sandblasting influence the roughness strongly compared to the aggregate surface. Also, the specific surface area of 4/8 aggregate is much larger than of the treated specimens. It is important to take this in consideration when using test results.

Developing a Project Evaluation and Testing Model to Assess Stable Photovoltaic Slicing Machine

Abstract: This study discusses and develops a project selection model for the purchase of diamond cutting machines for 12-in. photovoltaic silicon wafer slicing based on an analytical network process and preference by similarity to ideal solution (ANP-TOPSIS) method. Simultaneously, process capability indices are presented to test and verify the feasibility and effectiveness of the proposed method. The proposed method can help decision makers to establish a project evaluation and testing mode to affect and choose the best mode for diamond cutting machines of photovoltaic wafer slicing.

Study on Low-Temperature Cracking Performance of Asphalt Mortar Modified by an Aluminate Coupling Agent

Abstract: The low-temperature performance properties of asphalt mortar modified by an aluminate coupling agent (ACA) were investigated and are reported in this paper. An orthogonal experiment design method was used, and the creep stiffness and m-value were adopted as the indicators to investigate the modifier effects of the filler-asphalt ratio, ACA, and stearic acid on the low-temperature performance of asphalt mortar. The influence of other factors on the high-temperature, anti-rutting performance and intermediate-temperature fatigue performance of asphalt mortar was also evaluated. Analysis indicated that ACA could improve significantly the low-temperature performance and intermediate-temperature fatigue performance of asphalt mortar but reduced the high-temperature performance. Asphalt mortar modified by a moderate filler-asphalt ratio, a significant amount of ACA, and stearic acid showed better low-temperature performance properties.

Measurement of Very Low Creep Strains: A Review

Abstract: Various experimental techniques using mechanical springs for high strain sensitivity creep testing are described. A theory of stress and strain using these techniques is briefly summarized. Problems and advantages of the helicoid spring specimen technique are also analyzed. The helicoid spring specimen technique provides high efficiency for low-stress creep experiments in the self-loaded mode, while the external load mode allows extraordinary strain sensitivity. A new machine for conducting high-sensitivity torsion creep tests is presented together with some examples of creep curves obtained by the technique. The machine was designed to enable high sensitivity creep tests of inherently brittle materials such as intermetallics and ceramics.

Experimental determination of coupled thermal-mechanical effects on fracture toughness of sandstone

Abstract: In situ observations of the microscopic failure evolvement of sandstone under the coupled thermal-mechanical loadings were carried out by a scanning electron microscope (SEM). These results indicate that the effects of temperatures on cracking behavior and fracture toughness of sandstone are obvious. And, it is found that a critical transforming temperature is about 150°C for the fracture toughness of sandstone. That is, the fracture toughness value is to increase exponentially when the range of the temperature is from 25 to 150°C, but decreases exponentially when the range of the temperature is from 150 to 300°C. Therefore, in the present work the exponential relationships between fracture toughness and temperature are reported first. This is in good agreement with existing experimental evidence for the growth of micro cracks and thermal cracking.

Preliminary Study on Asphalt Emulsion Used in Cement Asphalt Mortar

Abstract: Asphalt emulsion is an important component in the preparation of cement asphalt mortar. In the work reported here, different emulsifiers and basic asphalts were used to manufacture emulsions and their properties were investigated. Results indicate that a diamine-based emulsifier renders asphalt emulsion that exhibits better compatibility with cement; lower density and higher ductility basic asphalt; and that styrene-butadiene-styrene modifiers are more appropriate in the manufacturing of emulsion.

Evaluation and Expression of Uncertainty in the Determination of Alumina in Deodorants Using Complexometric Method

Abstract: Recent studies reveal that aluminum has several adverse effects on human life and causes several diseases. There are various sources by which aluminum call enter into a human body: The deodorant is one of them, In this paper, the concentration of alumina (%Al(2)O(3)) has been assessed for three different deodorants (namely, A, B, and C) using all indirect complexometric method along with all uncertainty budget. The uncertainty in the measurement has been evaluated and expressed according to the requirements of the standard ISO/IEC 17025:2005. It has been identified that the uncertainty in the measurement arises mainly from repeatability, standardization of zinc acetate, and volume measurement, which have been evaluated and combined according to the EURACHEM guidelines. The concentrations of alumina were 0.81 +/- 0.01, 0.73 +/- 0.01, and 0.49 +/- 0.01 g per 100 mL, respectively, for A, B, and C deodorants. The uncertainty in the measurement varies from 1.2 % to 2 % for the three deodorants. The results show that a person using A and B brand deodorants receives, respectively, 65 % and 48 % higher exposure to aluminum on the skin than a person using the C brand.