Coefficient Of Thermal Contraction Research Articles

Evaluating the effects of cement asphalt emulsion paste as a grouting material on the fatigue and thermal contraction properties of semi-flexible asphalt composite pavement

Semi-flexible asphalt (SFA) composite pavement is widely used in pavement engineering for its high load-bearing capacity, enhanced durability, impermeability, and resistance to fuel and oil spillage. However, its cracking resistance remains a concern, influenced by repeated vehicle loads and thermal contraction stresses. This study investigates the impact of cement asphalt emulsion paste as a grouting material on SFA’s fatigue and thermal contraction. SFA specimens were grouted with cement paste (CP) containing 20%, 40%, and 60% asphalt emulsion. These specimens were subjected to indirect tensile strength, resilient modulus, and fatigue tests, along with evaluation of thermal contraction behavior using coefficient of thermal contraction. Results indicated that adding asphalt emulsion to CP enhances the flexibility and ductility of SFA but reduces its indirect tensile strength and stiffness modulus. A mathematical model was introduced to predict the resilient modulus based on indirect tensile strength tests. The fatigue analysis demonstrated significant difference in fatigue resistance between SFA and AC16 materials. Incorporating asphalt emulsion also improved SFA’s thermal contraction behavior.

Evaluating the low-temperature performance of asphalt mixtures based on the contraction and relaxation properties

The thermal cracking of asphalt pavement has been the focus of research in cold regions of the world. The contraction and relaxation properties of asphalt mixtures were crucial for investigating the thermal stress of asphalt pavement based on the thermal cracking mechanism. This paper proposed a novel evaluation index for characterizing the low-temperature performance of asphalt mixtures by considering their contraction and relaxation properties. Firstly, the rank during the evaluation indexes for low-temperature performance was determined by comparative analysis of method. Secondly, the thermal contraction coefficient was used to characterize contraction properties and cumulative stress at per unit strain rate (CSSR) was used to characterize relaxation properties in this paper. According to the cumulation process of thermal stress, a novel index was constructed based on the contraction and relaxation properties. Finally, considering the correlation between the failure temperature and the novel indexes, the prediction model of low-temperature performance consistent with the order of failure temperature was established based on the multiple linear regression method. Through the standardized analysis of the prediction model, the influence of novel indexes for the low-temperature performance of asphalt mixtures under different temperature conditions was clarified. A novel evaluation index provided a theoretical basis for unifying the evaluation indexes of asphalt mixtures.

Pressure tuning reverse martensitic transformation in the Mn0.9Co0.1NiGe half-Heusler alloy

Here we investigate the structural properties of the Mn0.9Co0.1NiGe half-Heusler alloys under pressure up to 12 GPa by Synchrotron angle-dispersive x-ray diffraction (XRD). At room temperature and pressure, the compound exhibits only the hexagonal NiIn2-type structure. Lowering the temperature to 100 K at ambient pressure induces an almost complete martensitic phase transformation to the orthorhombic TiNiSi-type structure. With increasing pressure, the stable orthorhombic phase gradually undergoes a reverse martensitic transformation. The hexagonal phase reaches 85% of the sample when applying 12 GPa of pressure at T = 100 K. We further evaluated the bulk modulus of both hexagonal and orthorhombic phases and found similar values (123.1 ± 5.9 GPa for hexagonal and 102.8 ± 4.2 GPa for orthorhombic). Also, we show that the lattice contraction induced is anisotropic. Moreover, the high-pressure hexagonal phase shows a volumetric thermal contraction coefficient α v ∼ −8.9(1) × 10−5K−1 when temperature increases from 100 to 160 K, evidencing a significant negative thermal expansion (NTE) effect. Overall, our results demonstrate that the reverse martensitic transition presented on Mn0.9Co0.1NiGe induced either by pressure or temperature is related to the anisotropic contraction of the crystalline arrangement, which should also play a crucial role in driving the magnetic phase transitions in this system.

Laboratory investigation of solid wastes combined with tunnel slag in cement stabilized base of asphalt pavement

To coordinate the disposal and resource utilization of bulk solid waste iron ore tailings sand (IOTS) and hazardous solid waste phosphogypsum (PG), this paper has carried out the research of using the two and the tunnel slag in the pavement base, including unconfined compressive strength, splitting strength, compressive resilience modulus, frost resistance, temperature shrinkage, and dry shrinkage tests. According to the characteristics of phosphogypsum (PG), the water stability, delayed compaction, and leaching of toxic substances were studied, and the mechanism was analyzed by SEM and XRD. It is concluded that tunnel slag and IOTS are great filling materials; The inclusion of PG inhibited the hydration of cement, which results in the reduction of unconfined compressive strength and splitting strength in the early stage, and the higher mean coefficient of thermal contraction; When the content of PG did not exceed 6%, the frost resistance, water stability, and drying shrinkage coefficient performed well, and the delayed forming strength had almost no loss, providing support for the continuous construction technology of the road base and the inhibition of reflective cracks. Applying a large number of solid wastes to road engineering can not only efficiently handle various waste buildup problems but also produce a new form of road materials with important social, economic, and environmental benefits.

Characterization of styrene-butadiene-styrene (SBS)-modified asphalt binders using the bending beam rheometer and the asphalt binder cracking device

The addition of styrene butadiene styrene (SBS) to asphalt binders has led to enhanced performance in pavements across the entire range of working temperatures. SBS-modified binders have also proven to be more difficult to characterize in terms of their rheological properties. Low-temperature properties of asphalt binders are typically evaluated using the bending beam rheometer (BBR), which was developed to measure creep stiffness. Recent refinements to the BBR analysis have led to the development of Δ Tc which is meant to provide more insight into the relaxation properties of the binder. The Asphalt Binder Cracking Device (ABCD) was developed to improve on this characterization by also taking into consideration the failure strength and coefficient of thermal contraction. Previous research has shown that the ABCD provides more valuable insight into the effect of SBS on the low-temperature properties of asphalt binders. This paper will evaluate the ability of these two low-temperature tests to characterize the performance of five different asphalt binders with increasing concentrations of SBS. It was found that the evaluation of the materials using Δ Tc was inconsistent with binder type and generally indicated that SBS reduced cracking resistance, while the ABCD critical temperature and the proposed Δ Tf parameter generally showed an improved correlation with SBS concentration.

Effect of 3D aggregate shape on thermo-mechanical properties of asphalt concrete using a mesostructure-based homogenisation method

ABSTRACT Morphological characteristics of aggregates have long been recognised as an essential factor influencing the thermo-mechanical behaviour of asphalt concrete. However, studies on accurate quantification of this influence are still very limited. For this reason, the present study developed a mesoscale finite element method to investigate the effects of three-dimensional (3D) aggregate shape on the complex modulus, thermal expansion coefficient, thermal conductivity, and mesoscale responses of asphalt concrete. An upscaling homogenisation method was adopted to predict the effective thermo-mechanical properties of asphalt concrete. The 3D true sphericity (3DTS) was used as an index to characterise the aggregate shape. The computational results showed that the temperature and loading frequency significantly affect the role of aggregate shapes in determining the effective dynamic modulus of asphalt concrete. The high-angularity aggregates can increase the deformation resistance of asphalt concrete under thermal load, and thus reduces the thermal contraction coefficient of asphalt concrete. However, aggregate shape has no significant effect on the thermal conductivity of the asphalt concrete. In addition, the asphalt concretes with less angular aggregates have stronger low-temperature damage resistance, while the aggregates with high angularity can improve the rutting resistance of asphalt pavements.

Proposed Changes to Asphalt Binder Specifications to Address Binder Quality-Related Thermally Induced Surface Damage

Superpave specifications address binder properties that may lead to rutting, transverse cracking, and fatigue damage with varying degrees of success. However, asphalt binder production and formulation has significantly changed and introduced much more variability in relation to quality since the development of the Superpave Performance-Grade system because of economic, technical, and environmental reasons. Consequently, aged-induced surface distresses under combined thermal and traffic loading have become the main challenge for highway agencies. Thermally induced surface deterioration appears in the form of traditional transverse cracking, block cracking, and raveling, or accelerating damage at construction joints. This study evaluated the limitations of the proposed linear viscoelastic (LVE) rheological cracking surrogates, such as ΔTc, R-value, and G-R parameters, and the ability of the Asphalt Binder Cracking Device (ABCD) failure test to overcome these limitations. ABCD is particularly appropriate to rank binder performance because the measured cracking temperature (Tcr) encompasses binder LVE properties, failure strength, coefficient of thermal contraction, and cooling rate. The proposed parameter (ΔTf = Tc(S = 300 MPa) from BBR—Tcr from ABCD) relates the failure temperature to the equi-stiffness temperature and gives credit to well-formulated and compatible polymer-modified binders expected to increase binder strength and strain tolerance. This paper proposes a specification framework based on both ΔTc and ΔTf, universally applicable, regardless of binder composition. Additionally, preliminary purchase specification limits for binders used in surface layers are proposed based on the analysis of 44 binders, 15 with corresponding field performance data. Obviously, as confirmed by a recent stakeholder workshop and industry feedback, these preliminary specification limits need further validation and possible adjustments to account for regional experience and local challenges.

A Composite Model for Predicting the Coefficient of Thermal Contraction for Asphalt Concrete Mixtures

Abstract Thermal cracking is one of the most prevalent types of distress found in asphalt concrete pavement sections. The coefficient of thermal contraction (CTC) is the intrinsic parameter that determines the thermal contraction of asphalt mixtures subjected to temperature drop. Thus, thermal stress and associated thermal damage are greatly affected by the CTC of the mixture. The direct measurement of a mixture’s CTC is the most reliable and at the same time cumbersome method for predicting the thermal contraction of asphaltic mixtures. In this study, for Level I analysis, we measured the CTCs of mixtures that have a wide range of properties and reported the data. In order to remedy the difficulties associated with directly measuring CTC, we herein propose a simple yet accurate composite model. The suggested approach enables pavement engineers to predict CTC values as the temperature drops. The formulation requires the mixture’s volumetric properties, elastic modulus, and CTC of the aggregate a priori. With regard to binder, the formulation requires the CTC and relaxation modulus as input parameters. This procedure constitutes the Level II analysis for which the binder CTC is required beforehand. A database that constitutes a basis for estimating binder CTC was developed from measurements reported in the literature. The database can be used to fill the value for binder CTC in the developed composite model for the sake of predicting mixture CTC. This procedure constitutes Level III analysis. Levels II and III only differ with respect to the input value for binder CTC. The CTC values from the measurements and predicted from the composite model (Levels II and III) are compared. In order to fully understand the effects of Level II and III errors in estimating mixture CTCs, we also compared the thermal stress obtained from the predicted and measured CTCs.

Low temperature characteristics of asphalt mixture based on the semi-circular bend and thermal stress restrained specimen test in alpine cold regions

Low-temperature crack resistance performance for preventing and controlling asphalt pavement cracking plays an important role in alpine regions. This study is to evaluate the low temperature characteristics of asphalt mixture in alpine cold regions. Three kinds of asphalt binders (SK90, SBS modified asphalt, SRA modified asphalt-an independent R & D type for the alpine cold regions) and three types of gradations (AC-13, AC-16, SMA-13) were selected. The fracture characteristics of asphalt mixtures based on the energy perspective were evaluated based on the semi-circular bend (SCB) test. The influences of asphalt binder type, gradation type, temperature and notch depth on the stress–strain curve were investigated. In addition, the thermal contraction coefficient of different kinds of asphalt mixtures were also analyzed. The temperature stress curves of asphalt mixtures were constructed based on the thermal stress restrained specimen test (TSRST). The results showed that the distribution characteristics of the coarse aggregate had a greater impact on the cracking path of the specimen. The asphalt mixture specimen exhibited brittle fracture at −15 °C and −35 °C, while it exhibited ductile failure at 15 °C based on the stress–strain curves. The unit reference fracture energy can be used as an effective index to evaluate the crack resistance. SRA asphalt mixture specimens had the largest fracture toughness and unit reference fracture energy. The higher the notch depth, the smaller the fracture energy; the fracture energy and the incision had a good linear correlation. The thermal contraction coefficients of SRA, SBS and SK90 asphalt mixtures were 10.46 × 10-6 ∼ 18.65 × 10-6/°C, 10.66 × 10-6 ∼ 22.85 × 10-6/°C, 13.45 × 10-6 ∼ 28.80 × 10-6/°C, respectively; they were closely related to the asphalt type and temperature, it changed exponentially under different temperatures. The freeze-break temperature was within a range and the difference was within 5 °C. SMA-13 had the strongest low-temperature crack resistance, followed by AC-16, and AC-13.

Three-dimensional microstructure based model for evaluating the coefficient of thermal expansion and contraction of asphalt concrete

The coefficient of thermal expansion (CTE) and contraction (CTC) are critical parameters for pavement design and thermal analysis. This paper develops a 3-D microstructure-based FE model to evaluate the CTE and CTC of asphalt concrete. The 3-D random microstructure of asphalt concrete was generated with an image-aided algorithm. In the presented algorithm, the random 3-D geometry of a single aggregate was generated with a single 2-D image captured by Aggregate Image System 2 (AIMS2). The randomly generated 3-D aggregates were packaged with PFC 3D to construct the 3-D microstructure for asphalt concrete with prescribed gradation. Then the 3-D microstructure of asphalt concrete was imported into FE software ABAQUS to calculate the CTE and CTC. To validate the results from the numerical simulation, a laboratory experiment was conducted to test the CTE/CTC of the asphalt concrete with the same material composition. With the validated FE model, the effect of aggregate type, shape, and spatial orientation on the CTE/CTE was analyzed. Results show that the relative differences between the average values of numerical and experimental data were 1.63%∼4.64% for the CTE, and 3.01%∼7.20% for the CTC. With the increase of temperature, the CTE first decreased and then increased, while the CTC first increased and then decreased. Compared with the 3-D microstructure-based model, both the 2-D plain stress and plain strain models tended to overestimate the CTE of asphalt concrete. When the aggregate orientation tended to be inclined to a certain direction, the CTC and CTE of the asphalt concrete parallel to that direction tended to be smaller. Asphalt concrete prepared with quartz gravels and sand stones tended to have higher CTC and CTE. While the CTC and CTE of asphalt concrete could be reduced by using limestones.

Critical Current Under Uniaxial Strain on High-Pressure Heat Treatment Bi-2212 Round Wire

China Fusion Engineering Test Reactor project (CFETR), the next generation of Tokamak, has been incorporated into the important development of nuclear fusion in the future. Compared to the low temperature superconducting materials, Bi-2212 is one of the most promising superconducting materials due to the high irreversible field and outstanding current-carrying capacity. In particular, its critical properties can be improved dramatically by high-pressure heat treatment, which could enlarge its application range. The critical current performance of Bi-2212 round wire (RW) with high-pressure heat treatment under uniaxial strain are studied at 4.2 K in 12 T background field at Institute of Plasma Physics, Chinese Academy of Science (ASIPP). All samples are provided by Northwest Institute for Non-ferrous Metal Research (NIN) in China with new techniques. The results showed that samples with 1 bar pressure heat treatment presented a more drastic degradation under compressive and tensile stress than that the samples heat-treated with 30 and 50 bar pressure. In order to study the influence of different thermal contraction coefficient between the substrate and sample, two springs with different materials were used for the experiment. According to the results, it was found that Cu-Be alloy spring is more compatible for Bi-2212 RW than Ti-6Al-4V alloy spring. In this paper, the experiment setup and results are fully presented.

Universal and practical approach to evaluate asphalt binder resistance to thermally-induced surface damage

Economic drivers, changing material streams, environmental regulations, and formulation changes driven by the climate-based PG grading system itself have led to substantial changes in the production and modification of paving grade asphalt since the development of Superpave Performance-Graded (PG) binder specifications during the 1990s. Superpave specifications and mechanistic-empirical pavement design criteria attempt to address pavement distresses such as rutting, transverse cracking, and fatigue damage with varying degrees of success. Unexpectedly though, aged-induced surface distresses have worsened to become the primary cause of pavement damage for many highway agencies. Thermally-induced surface deterioration, which may not be directly linked to traffic loading, appears in the form of traditional evenly spaced transverse thermal cracking, block cracking, raveling, or accelerating damage at joints or other areas where density is insufficient to prevent moisture and oxygen from permeating into the asphalt surface layer. The source of damaging stresses leading to such failures are not well-understood, nor have binder properties contributing to early pavement surface damage been completely and effectively controlled by PG specifications.Transverse cracking damage is known to require external restraint in one-dimension to impose tensile stresses on the asphalt concrete mixture as it cools and contracts. Recent experimental results from mixture bending beam testing (BBR Sliver), acoustic emissions, and finite element analysis (FEA) provide evidence that asphalt concrete can be damaged on cooling even when no external restraint is imposed. A second “Internal Restraint” damage mechanism has been theorized to create localized tensile stresses due to differential contraction between mastics and the surrounding aggregate skeleton as a pavement surface cools. This recently proposed concept is now thought to be one of the primary causes for surface block cracking and raveling. Moreover, damage accumulating via the internal restraint mechanism acts cumulatively with other sources of stress on the mixture, such as the top-down fatigue cracking that initiates near the tires edge, transverse cracking due to externally restrained cooling, thermal fatigue cycling without sufficient healing, longitudinal cracking at the construction joints or reflective cracking from cracks in the underlying layer that propagate through the overlays at the surface.Other researchers have proposed various rheological parameters measured in the linear-viscoelastic region (LVE) to be indicators of problematic binders that are prone to age-induced surface damage. Most of these parameters can be fundamentally or empirically related to binder stress relaxation properties at low temperatures. Although these LVE rheological surrogates can be used to rank binder performance for straight-run asphalts produced by conventional vacuum distillation, these materials typically have a narrow strain tolerance and strength range. Limitations of LVE parameters, such as ΔTc, R-value, or G-R parameter, are more noticeable when used to characterize the performance of complex binders. This study indicates that rheological surrogates in the LVE region are not a direct measure of binder failure properties such as strength, ductility, strain tolerance, fracture toughness, or fatigue resistance, particular after a bitumen has been modified with polymers (PMA). Hence, rheological surrogates within the LVE domain are important, but not sufficient for a universal and blind approach to evaluate binders without knowing their composition or production process. LVE surrogates alone cannot rank performance for a wide range of complex systems such as incompatible blends, recycled materials (crumb rubber, shingles, plastics, biomaterials) or PMA’s using the same thresholds for pass/fail specifications. This paper proposes a practical approach to rank a binder’s resistance to low-temperature age-induced surface damage by combining LVE rheological measurements with failure parameters using the Asphalt Binder Cracking Device. ABCD is particularly appropriate to ranking surface damage via the internal restraint cooling model because the binder cracking temperature measured in this test depends upon both failure strength, cooling rate, and the binder’s coefficient of thermal contraction (CTC).

Viscoelastic finite element evaluation of transient and residual stresses in dental crowns: Design parametric study

Porcelain-veneered zirconia (PVZ) are one of the popular choice for crown restorations. Veneer layer of these dental restorations, however, is susceptible to chipping and delamination due to the development of transient and residual stresses during the cooling phase of veneer firing. The aim of this study is to elucidate the effect of material property mismatch, veneer to core thickness ratio, and cooling rate on these transient and residual stresses of PVZ restorations. Three-dimensional viscoelastic finite element modelling (VFEM) was performed. The VFEM model was developed using the UEXPAN subroutine in ABAQUS software and was validated for transient and residual stresses in a sandwich seal problem with experimental data available. A good agreement between the simulated VFEM results and experimental data was obtained. Using validated VFEM, two PVZ systems (PM9/zirconia and ZirPress/zirconia), three veneer to core thickness ratios (2:1, 1:1 and 1:2), and two cooling rates controlled slow cooling at 1.74E-5 W/mm2°C (i.e. ~30 °C/min) and fast bench cooling at 1.74E-4 W/mm2°C (i.e. ~300 °C/min) were used. The results showed that PM9/zirconia has smaller thermal contraction mismatch, resulting in lesser residual stress (33.36 MPa) as compared to ZirPress/zirconia (37.94 MPa) for controlled cooling and 2:1 veneer to core ratio. In addition, in both systems with the decrease in veneer thickness, we observed a decrease in residual stresses developed. We also observed some effect of cooling rate on residual stresses. The controlled cooling resulted in lower residual stress (24.35 MPa) for PM9/zirconia with a 1:1 veneer to core thickness ratio as compared to bench cooling (28.04 MPa). The effect of cooling rate was more evident on transient stresses. For instance, in the PM9/zirconia with 1:1 thickness ratio model, the difference in transient stresses was 9.93 MPa between controlled and bench cooling. Therefore, properties such as elastic modulus and coefficient of thermal contraction (CTC), as well as the thickness ratio and cooling rate all play an important role in transient and residual stresses developed in the studied ceramic systems.

Spatial control of heavy-fermion superconductivity in CeIrIn5.

Although crystals of strongly correlated metals exhibit a diverse set of electronic ground states, few approaches exist for spatially modulating their properties. In this study, we demonstrate disorder-free control, on the micrometer scale, over the superconducting state in samples of the heavy-fermion superconductor CeIrIn5 We pattern crystals by focused ion beam milling to tailor the boundary conditions for the elastic deformation upon thermal contraction during cooling. The resulting nonuniform strain fields induce complex patterns of superconductivity, owing to the strong dependence of the transition temperature on the strength and direction of strain. These results showcase a generic approach to manipulating electronic order on micrometer length scales in strongly correlated matter without compromising the cleanliness, stoichiometry, or mean free path.

Significant strengthening of a lithium disilicate glass by Li+/Na+ exchange at substantially lowered temperature

A lithium disilicate (LD) glass with stoichiometric composition and glass transition temperature (Tg) ∼ 470 °C was ion-exchanged over a wide temperature range below the Tg. The ion-exchange temperatures used were 380 °C or 315 °C in a pure molten NaNO3 bath, and 235 °C in a molten mixed salt bath of 50 mol% NaNO3＋50 mol% KNO3. Temperature-dependences of surface layer morphology and mechanical behavior of the ion-exchanged glass were investigated. It was found that similar surface Na+ concentrations were presented on the glass after the ion-exchange at all the three temperatures for different times. Surface failure occurred on the glass after the treatments at the two higher temperatures for longer time to increase the ion-exchanged depth. The surface failure could be completely avoid by substantially lowering the temperature to 235 °C in the mixed salt bath for much longer time to obtain a similar level of case depth. Similar strengthening effects were exhibited at the three temperatures as the ion-exchanged depth was shallower. With further increasing the depth, however, much more significantly strengthening effect could be achieved at the substantially lowered temperature. Flexural strength of the glass could be enhanced from ∼ 97 MPa to ∼ 520 MPa after the treatment at 235 °C for 128 h. The temperature-dependent effect to strengthen the LD glass by Li+/Na+ exchange was attributed to the combined effect of stress relaxation during ion-exchange and thermal contraction coefficient mismatch between the ion-exchanged surface layer and the internal bulk glass.

Viscoelastic finite element analysis of residual stresses in porcelain-veneered zirconia dental crowns.

The main problem of porcelain-veneered zirconia (PVZ) dental restorations is chipping and delamination of veneering porcelain owing to the development of deleterious residual stresses during the cooling phase of veneer firing. The aim of this study is to elucidate the effects of cooling rate, thermal contraction coefficient and elastic modulus on residual stresses developed in PVZ dental crowns using viscoelastic finite element methods (VFEM). A three-dimensional VFEM model has been developed to predict residual stresses in PVZ structures using ABAQUS finite element software and user subroutines. First, the newly established model was validated with experimentally measured residual stress profiles using Vickers indentation on flat PVZ specimens. An excellent agreement between the model prediction and experimental data was found. Then, the model was used to predict residual stresses in more complex anatomically-correct crown systems. Two PVZ crown systems with different thermal contraction coefficients and porcelain moduli were studied: VM9/Y-TZP and LAVA/Y-TZP. A sequential dual-step finite element analysis was performed: heat transfer analysis and viscoelastic stress analysis. Controlled and bench convection cooling rates were simulated by applying different convective heat transfer coefficients 1.7E-5 W/mm2 °C (controlled cooling) and 0.6E-4 W/mm2 °C (bench cooling) on the crown surfaces exposed to the air. Rigorous viscoelastic finite element analysis revealed that controlled cooling results in lower maximum stresses in both veneer and core layers for the two PVZ systems relative to bench cooling. Better compatibility of thermal contraction coefficients between porcelain and zirconia and a lower porcelain modulus reduce residual stresses in both layers.

Fracture behavior analysis of EuBaCuO superconducting ring bulk reinforced by a stainless steel ring during field-cooled magnetization

We have magnetized the EuBaCuO ring bulk reinforced by a stainless steel ring during field-cooled magnetization (FCM) at 50 K under the magnetic fields from 6.3, 7.3 or 8.3 T, in which the ring bulk was broken at the intermediate step of FCM from 8.3 T. To discuss the fracture behavior of the bulk, we have performed the numerical simulation using a three dimensional finite element method for the bulk with realistic superconducting characteristics, and obtained both the electromagnetic hoop stress, during FCM and thermal hoop stress, under cooling from 300 to 50 K. The difference of the thermal contraction coefficient between the bulk and the stainless steel ring caused an inhomogeneous profile with a tensile stress at the outermost edge on the bulk surface under cooling process. The maximum of the total hoop stress, was estimated to be +50 MPa and +59 MPa during FCM from 7.3 T and 8.3 T, respectively. These results suggest that the actual fracture strength of the present ring bulk is between 50 and 59 MPa. The value should be reduced as low as possible in the whole area of the bulk to avoid the fracture behavior during FCM.

Towards the local expansion and contraction measurement of asphalt exposed to freeze-thaw cycles

This paper aims at analyzing the local strain fields in several asphalt mixtures exposed freeze-thaw cycles. Four types of asphalt with different Recycled Asphalt Pavement (RAP) content (0%, 20%, 40%, and 100% of RAP) were considered. They were subjected to freeze-thaw cycles, in the temperature range of −11°C and 20°C. The local contraction/expansion of these samples during the cooling/heating was measured using the Grid Method (GM) and Digital Image Correlation (DIC). The strain distribution is very heterogeneous due to the difference between the thermal contraction coefficients of aggregates and mastic (i.e., bitumen and filler). The thermal responses of the mixture under study were compared at the micro- and the macro-scales.

Simulation studies of mechanical stresses in REBaCuO superconducting ring bulks with infinite and finite height reinforced by metal ring during field-cooled magnetization

We have performed the numerical simulation of mechanical stresses (hoop stress, σθ and radial stress, σr) in REBaCuO ring bulks with an infinite and finite height reinforced by metal (aluminum alloy or stainless steel) ring during field-cooled magnetization (FCM) using a solenoid coil with an infinite and finite height. The superconducting characteristics of the bulk material were assumed to follow Bean’s critical state model. The electromagnetic hoop stress, of the finite height ring bulk during FCM using the infinite coil was larger than that for the infinite ring bulk, and the time step dependence of was clearly different in each case. The value was reduced by the reinforcement by the metal ring, and the stainless steel ring was more effective than the aluminum alloy ring. The value of the finite ring bulk magnetized using the finite coil was slightly reduced, compared to magnetization using the infinite coil. The thermal hoop stress, which occurs in the ring bulk when cooling down to operating temperature due to the difference of thermal contraction coefficient between ring bulk and metal ring, was also estimated. The compressive, , was reduced comparatively at the uppermost surface of the ring bulk because of the larger thermal contraction of the metal ring along the axial direction. The actual total hoop stress, was analyzed for the finite ring bulk reinforced by the metal ring during FCM and the possibility of mechanical fracture due to this hoop stress is also discussed.

Factors affecting the properties of composites made by 4D printing (moldless composites manufacturing)

3D printing is the process where layers of materials are deposited to make structures of complex geometries. 4D printing is a process that combines 3D printing with the application of some activating agent in order to change the shape of the manufactured part after the process, e.g. the flat structure will change its shape to take up the desired complicated shape such as “curved” or “S” shaped. As such the 3D printing process does not have to spend time to print the intricate parts, and the process can be faster. The requirement for 4D printing is that materials with special characteristics that are responsive to an activating agent need to be used. 4D printing of composites utilizes the same concept of 4D printing, except that the materials used are long fiber composite materials. 4D printing of composites utilizes the shrinkage of the matrix resin, and the difference in coefficients of thermal contraction of layers with different fiber orientations to activate the change in shape upon curing and cooling. This behavior can be used to make parts with curved geometries without the need for a complex mold. As such manufacturing of pieces of curved shapes can be fast and economical. However, the degree of shape changing depends on the material properties, the fiber orientation, the lay up sequence and the manufacturing process. This paper presents the results obtained from a study on the effects of these aspects on the shape of the curved parts.