Surface Temperature Of Specimens Research Articles

Self-heating curing and its influence on self-sensing properties of ultra-high performance concrete with hybrid stainless steel wires and steel fibers

This study aims to develop ultra-high performance concrete (UHPC) with self-heating curing and self-sensing properties by incorporating hybrid stainless steel wires (SSWs) and steel fibers (SFs) to advance the safety, function/intelligence, and resilience of infrastructures. 0.2 vol% SSWs with micro diameter can already form overlapped conductive network inside UHPC together with SFs to decrease the electrical resistivity and enhance high-efficiency conversion rate from electric energy to Joule heat. As 20 W input power is applied and sustained, the electrical resistivity of UHPC with hybrid 0.2 vol% SSWs and 1.6 vol% SFs (W02F16) first decreases from 45.1 Ω∙cm to 8.3 Ω∙cm and then to 7.88 Ω∙cm due to the field emission effect and the microscopic thermal expansion of SSWs. The surface temperature of W02F16 specimens reaches 78.6 ℃ for 73 minutes self-heating with an average heating rate of 0.821 ℃/min and a temperature difference lower than 11.6 ℃. Meanwhile, the fractional change in electrical resistivity and sensitivity corresponding to peak flexural stress of W02F16 after 8 h self-heating curing can reach 58.3 % and 3.22 %/MPa, higher 2.1 and 3.6 times than that after 28 d standard curing. Furthermore, self-heating curing UHPC composites at 28 d possesses more stable and sensitive self-sensing performance especially within pre-peak flexural stress period, resulting from the coarsening effect of direct current on SSWs’ interface to regulate and control of conductive pathway in concrete. This is the innovative demonstration that self-heating curing process can endow hybrid SSWs and SFs reinforced UHPC with stable/high self-sensing sensitivity to rapidly fabricate multifunctional/smart infrastructures with the abilities of structural health monitoring, snow and ice self-melting, and indoor heating.

Online and Ex Situ Damage Characterization Techniques for Fiber-Reinforced Composites under Ultrasonic Cyclic Three-Point Bending.

With ultrasonic fatigue testing (UFT), it is possible to investigate the damage initiation and accumulation from the weakest link of the composite material in the very high cycle fatigue (VHCF) regime in a shorter time frame than conventional fatigue testing. However, the thermal influence on the mechanical fatigue of composites and the scatter in fatigue data for composites under ultrasonic cyclic three-point bending loading still need to be investigated. In this study, we conducted interrupted constant-amplitude fatigue experiments on a carbon-fiber satin-fabric reinforced in poly-ether-ketone-ketone (CF-PEKK) composite material. These experiments were carried out using a UFT system, which operates at a cyclic frequency of 20 kHz with a pulse-pause sequence. Various parameters, such as the CF-PEKK specimen's surface temperature, acoustic activity, and the ultrasonic generator's input resonance parameters, were measured during cyclic loading. During experiment interruption, stiffness measurement and volumetric damage characterization in the CF-PEKK specimens using 3D X-ray microscopy (XRM) were performed. The locations of damage initiation and accumulation and their influence on the changes in in situ parameters were characterized. Under fixed loading conditions, damage accumulation occurred at different locations, leading to scattering in fatigue life data. Further, the damage population decreased from the surface to the bulk of the composite material.

Thermoelectric properties of cement mortar doped with steel fiber under heating conditions

In order to supply the multifunctional demand for building materials in modern construction industry, research on the thermoelectric properties of cement mortar mixed with steel fibers (diameter 0.22 mm) for engineering purposes has been carried out in this paper. The self-built thermoelectric response test system is used to collect the thermoelectric power, surface temperature and conductivity of the cement-based composite specimens in real time. Based on the comparative measurement method, the thermal conductivity of large-sized specimens was obtained. The effect of different SF content on thermal conductivity, Seebeck coefficient and ZT of the specimens were investigated. The results show that the specimens doped with steel fiber is p-type thermoelectric material, and the maximum value of thermoelectric figure of merit ZT of the cement mortar doped with 7.5 wt% steel fiber at 50℃ is 0.175. The ZT of cement mortar specimens mixed with steel fibers is relatively low, but it has good application prospects as a low-cost and widely used building material.

The Law and Mechanism of the Effect of Surface Roughness on Microwave-Assisted Rock Breaking

In physical engineering, a rock surface, whether naturally or artificially formed, is rough. When irradiating rocks, microwaves produce reflections and diffractions on the surface of rough rocks, which significantly affect the absorption of microwave energy by rocks, thus influencing the result of microwave irradiation. In order to explore the influence of rough rock surfaces on the effect of microwave-assisted rock breaking, microwave irradiation tests were carried out on basalt samples with different values of roughness to test the temperature and P-wave velocity of the samples before and after microwave irradiation. Numerical test methods were used to systematically study the influence of rough rock surfaces on microwave irradiation. The results show that, under the same microwave irradiation conditions, the effect of microwave irradiation on rough surface basalt is more significant than that of flat surface basalt. The surface temperature distribution range of flat surface specimens is narrow, the surface temperature range of rough surface specimens is wider and more inhomogeneous, and the maximum surface temperatures of rough surface specimens are much higher than those of flat surface specimens. After irradiation, new macroscopic cracks were generated on the surface of the samples, and the crack propagation of the rough surface samples was more obvious. The decrease in P-wave velocity before and after the irradiation of flat surface samples is small, and that of rough surface samples is larger. The main factors affecting the effect of microwave irradiation on the rough surface are the refraction and reflection of electromagnetic waves, heat conduction, and stress concentration on the surface.

Thermal Behavior of Carbon-Phenolic/Silica Phenolic Dual-Layer Ablator Specimens through Arc-Jet Tests.

We studied the behavioral characteristics of a newly developed dual-layer ablator, which uses carbon-phenolic as a recession layer and silica-phenolic as an insulating layer. The ablator specimens were tested in a 0.4 MW supersonic arc-jet plasma wind tunnel, employing two different shapes (flat-faced and hemispherical-faced) and varying thicknesses of the carbon-phenolic recession layer. The specimens underwent two test conditions, namely, stationary tests (7.5 MW/m2, ~40 s) and transient tests simulating an interplanetary spacecraft re-entry heat flux trajectory (6.25↔9.4 MW/m2, ~108 s). During the stationary tests, stagnation point temperatures of the specimens were measured. Additionally, internal temperatures of the specimens were measured at three locations for both stationary and transient tests: inside the carbon-phenolic recession layer, inside the silica-phenolic insulating layer, and at the recession layer-insulating layer intersection. The hemispherical-faced specimen surface temperatures were about 3000 K, which is about 350 K higher than those of flat-faced specimens, resulting in higher internal temperatures. The recession layer internal temperatures rose more exponentially when moved closer to the specimen stagnation point. Layer interaction and insulating layer internal temperatures were found to be dependent on both the recession layer thickness and the exposed surface shape. The change in exposed surface shape increased mass loss and recession, with hemispherical-faced specimens showing ~1.4-fold higher values than the flat-faced specimens.

Experimental study on self-heating phenomena of CMDB/HTPB propellant under intermediate strain rate compression load

Self-heating behaviour of solid propellants under intermediate strain rate compressive loading have been studied. Effects of two intermediate strain rate (1 s-1 and 150 s-1) of the CMDB/HTPB propellants were investigated. The compression test was conducted using a hydraulic testing machine and the self-heating temperatures were measured by an infrared camera. The results show the following: (1) For CMDB propellant, the surface temperature of specimens rapidly increased at the initial period, then decreased due to the movement of the high temperature region caused by deformation, and then increased again. Finally, the surface temperature slowly decreased due to heat transfer to the surroundings. Infrared thermography showed the formation of a hot spot. Cracks were initiated and gradually expanded to the interior area during compression. (2) For HTPB propellant, the surface temperature of specimens increased slightly. Compared with CMDB specimens, there was no significant damage to HTPB specimens. (3) For both CMDB and HTPB propellants, the temperature distribution of specimens was non-homogeneous. At the centre of the specimen surface, the temperature is the highest. The self-heating temperatures of propellant increased with increasing the strain rate. However, the difference is slight for HTPB propellant, whereas it is considerable for CMDB propellant.

Combined Surface Heating by Laser Beam and Subsonic Nitrogen Plasma Jet

The paper describes new combined heating capability of the IPMech RAS inductively coupled plasma facility VGU-4. A 200 W ytterbium laser was added to the facility as a source of radiative heating. The cylindrical specimen made of the Buran orbital vehicle’s heat-shielding tile material with a black low catalytic coating was exposed to subsonic pure nitrogen plasma jet and laser radiation. The specimen surface temperature reached 1325 ∘C during combined radiative and convective heating. The maximum heat flux obtained in the combined mode for a laser incident power of 47 W and a VGU-4 HF-generator anode power of 22 kW was 32.1 W/cm2. The convective heat flux from the nitrogen plasma jet at the same anode power was 12.6 W/cm2. Adding a laser to an existing inductively coupled plasma facility gives the future opportunity to better simulate entry into the atmospheres of Mars, Venus, the outer planets and their moons.

Sliding contact performance of injection moulded and selective laser sintered polyamide under dry and lubricated conditions

PurposeThis paper aims to understand the effect of the manufacturing process on the frictional and wear performance of polyamide.Design/methodology/approachPin specimens were manufactured through injection moulding (IM) and selective laser sintering (SLS) manufacturing processes. The friction and wear performance was evaluated using a pin-on-disc configuration under dry and oil-lubricated conditions. The friction coefficient, wear resistance and surface temperature of specimens were measured, and failure morphology analysis was carried out to understand the mechanism.FindingsSLS material exhibited significantly less friction, wear and surface temperature than IM material under dry conditions. Reduced ductility due to the sintering contributes to reduced friction, wear and heat generation. Under the dry condition, IM material exhibited plastic flow and roll-shaped deformation, whereas SLS material exhibited only local degradation due to its lesser ductility. Lubrication reduced friction and temperature for both SLS and IM materials. The porous nature of the sintered surface absorbed the lubricant and released it while sliding, which is confirmed by the brown-coloured wear track.Originality/valueThe study provides valuable input to the designers on the sliding contact performance of commonly adopted two different manufacturing processes of polymers; IM and SLS manufacturing.

Heat Dissipation Behavior of a Low-Strength-Steel Welded Joint in Ultrasonic Fatigue

The coupled effects of heat and frequency in very-high-cycle fatigue are known under ultrasonic testing, while the heat dissipation behavior of welded joints is less investigated. In this work, the specimen surface temperature of a low-strength-steel welded joint and its base metal were monitored by infrared thermal imaging technique under ultrasonic fatigue loading. Results showed that the surface temperature distribution of both welded and base metal exhibited a parabola shape, and the temperature evolved with three stages. The location of the highest temperature within the weld metal correlated well with fatigue failure location. The inhomogeneity and asymmetry of temperature distribution implied a dominant role for heat transfer mode and insignificant influence of microstructure heterogeneity or specimen type. The nature of heat dissipation in low-strength steel in ultrasonic fatigue was thermal–mechanical coupling effect, which should be paid close attention in the standardization of ultrasonic fatigue testing.

Effect of Al addition on the single and cyclic ablation properties of C/C–SiC composites

This article focuses on the damage behavior and mechanism of aluminum addition on reactive melt infiltrated C/C–SiC composites in single and cyclic ablation environments. Plasma ablation tests were performed on C/C–SiC composites containing 20 wt % and 40 wt % aluminum respectively. Coupled with TMA, XRD, SEM and EDS, the results showed that composites with 40 wt % Al had better ablation resistance during the cyclic ablation, while the composites with 20 wt % Al had excellent ablation damage resistance during a single ablation. This difference was due to higher number of microcracks formed inside the composites containing 40 wt % Al than 20 wt % Al, the lower specimen surface temperature during ablation, and the thermal stresses can be released by pore crack expansion during gas reciprocal loading. While in the single continuous loading of gas, the 20 wt % Al composite formed a protective oxide layer with smaller pores and fewer gas and oxygen entry channels, resulting in good resistance to ablation.

Characterization of Thermal Barrier Coatings Using an Active Thermography Approach

The aim of this paper is to define and set up an experimental procedure, based on active thermography, for the characterization of coatings for industrial applications. This procedure is intended to be a fast and reliable method, alternative to the consolidated one described in International Standards. In more detail, a classical active thermographic set up, and not a dedicated apparatus, was used for that aim, and data processing techniques referred to the analytical approach described in Standards. The active thermography procedure provided the measurement of the surface temperature of specimens undergoing a thermal excitation, applied by means of a laser pulse (Pulsed Technique). Temperature data processing, according to and adapting the Standard procedures, allowed to obtain thermal conductivity and diffusivity information. In particular, two coating processes (Atmospheric and Suspension Plasma Spray) applied to the same base material, Inconel 601, and the same coating material were investigated. These results were compared in terms of thermal properties variation with respect to base and coated materials, and in terms of different coating processes (APS and SPS). Obtained results were also compared to those available in literature.

Identification of the thermal conductivity tensor for transversely isotropic materials

AbstractThe knowledge of the thermal conductivities is of particular interest for the thermo‐mechanical modeling of transversely isotropic composite materials. Hence, the identification of these material parameters by solving an inverse problem is significant, as they cannot be directly measured. In this study, a suitable experimental setup is presented, where infrared thermography is used to measure the surface temperatures of thin specimens. Further, a local identifiability concept is employed to study whether locally unique parameters can be obtained. This leads to a particular step‐wise identification concept. The parameter identification is performed applying a nonlinear least‐square approach and finite elements. In the step‐wise identification process the convection coefficient is required first, and, subsequently, the coefficients of the thermal conductivity tensor are determined. Due to the step‐wise identification, the uncertainties of previously identified parameters have to be considered in the subsequent identification steps. The resulting uncertainties are estimated using the Gaussian error propagation concept. It turns out that the thermal conductivities of transversely isotropic materials are generally identifiable from surface temperature data. Furthermore, since all uncertainties have an essential influence on the results of real numerical simulations, their error propagation should be considered in resulting boundary‐value problems. Thus, the uncertainty quantification is demonstrated by a validation experiment.

Experimental investigation on in-plane shear fatigue failure criteria of ± 45˚ angle-ply carbon epoxy composite

Designing load-bearing composite elements significantly relies on the material's response under different loading conditions, particularly fatigue. To improve the fatigue life prediction of composite structures, one of the role-playing properties, the in-plane shear properties variation, is focused on in this paper. Because of the ± 45˚ angle-ply tensile fatigue test advantages in terms of reliability and cost-efficiency, several fatigue experiments are conducted at certain stress levels using [±45]2s T300/L20 Carbon/Epoxy laminates. The surface temperature of specimens was measured using an infrared thermography camera during the fatigue test of Carbon/Epoxy composites. A strain-based fatigue life criterion capable of predicting the in-plane shear life is presented. The suggested maximum 5 percent strain limit could distinguish the in-plane shear fatigue failure from final laminate fracture. Furthermore, tangent shear modulus, secant shear modulus, strain energy density per cycle and cumulative strain energy density results approved the proposed strain-based life model, while each could be considered as a distinct criterion.

Ignition and burning of the composite sample impacted by the Bunsen burner flame: A fully coupled simulation

Experimental study and three-dimensional simulation of warming up, ignition, and subsequent burning out of the composite material impacted by the attached Bunsen burner flame is presented. The specimen is the fiberglass-reinforced composite with the epoxy resin binder. In the experiment, vertical specimen was located above the laminar diffusion flame, and transient variation of specimen mass and surface temperatures was recorded until the matrix polymer burned out. In the simulations, thermal decomposition of the composite was evaluated by the in-house pyrolysis model Pyropolis coupled with the general-purpose CFD solver, which simulated the flames generated by the burner and by the combustible volatiles. Formal kinetics of thermal decomposition of matrix polymer and the heat of combustion of volatiles have been derived from the microscale combustion calorimetry measurements. The simulation results include favorable comparisons of experimental and predicted dynamics of material degradation and flame behavior. Transient spatial distributions of surface temperature, burning rate, and heat fluxes (net, radiative and convective) are demonstrated. This study is the step towards developing the computational framework capable of replicating and predicting the outcome of standard fire tests UL94 and VBB.

On the kinetic formulation of fracture fatigue entropy of metals

AbstractThe kinetic concept of the strength of solids is used to determine the fatigue life of stress‐controlled cyclic loading and evaluate the fracture fatigue entropy. Unlike the traditional stress or strain‐based models, this theory uses the applied stress amplitude and the specimen's surface temperature to determine the lifetime. The degradation fraction in each cycle is used to calculate the life cycle. Then the material parameters of the final life equation are obtained for two materials: low carbon steel 1018 and aluminum 7075‐T6. The number of cycles to fracture and the cyclic plastic strain energy ( ) are used to calculate the fracture fatigue entropy (FFE). It is shown that the life cycle prediction of the proposed model agrees well with the experimental results from the literature. Results provide further evidence for the constancy of FFE.

Controlling the Specimen Surface Temperature During Irradiation With a Submillisecond Electron Beam Produced by a Plasma-Cathode Electron Source

In this article, the experimental and theoretical data are presented which demonstrate the possibility of controlling the specimen surface temperature during irradiation with a submillisecond electron beam produced by a plasma-cathode electron source. The specimen surface temperature is controlled by modulating the beam current via appropriate short-time variations in the emission plasma parameters. The temperature ripple factor, measuring less than 5% in our experiments, is defined as the product of the specimen surface temperature and the discretization degree of the beam current and its pulse duration. The efficiency of the method of temperature control is confirmed by numerical simulations. The proposed method opens the way to new applications of plasma-cathode electron sources in science and technology.

Heat Transfer Behavior During Water Spray Quenching of 7xxx Aluminum Alloy Plates

AbstractThe desired microstructure and mechanical properties of heat treatable 7xxx aluminum alloy can be achieved after spray quenching by controlling spray parameters. However, heat transfer behavior between specimen and quenchant is transient and complicated in quenching process. In this paper, a spray quenching system was utilized to quench for 7xxx aluminum alloy. The influence of spray parameters, including spray pressure and spray distance, on heat transfer behavior was examined and discussed. Heat flux (HF) and heat transfer coefficient (HTC) were calculated by iterative method. The results indicated that the aluminum alloy experienced transition boiling, nucleate boiling, and convection cooling regimes during spray quenching process. Heat transfer capability first increased and then decreased with the increasing of spray pressure or spray distance. A function of local heat transfer coefficient (L-HTC) which is variable in specimen surface temperature, spray parameters, and spatial location was constructed. Residual stress of 7xxx aluminum alloy plates was increased first and then slightly differed with the increase of volumetric flux.

Chloride-Induced Stress Corrosion Cracking Tester for Austenitic Stainless Steel

Abstract In this paper, a new experimental tester was designed to improve the stability in load measurement and imposed environment for chloride-induced stress corrosion cracking (CISCC) testing of austenitic stainless steels that are used to construct spent nuclear fuel dry storage canisters. By fabricating compact tension specimens using the UNS S30400 stainless steel, the test is conducted by immersing the specimen in 5 % salinity artificial seawater at 50°C. From the measured load, the stress intensity factor is calculated and the crack length is measured by an optical microscope. The present experimental data confirm the existing findings that the CISCC growth rate is insensitive to the stress intensity factor but is dominantly affected by the specimen surface temperature. The crack growth rate also confirms the existing model.

Change of Specimen Temperature during the Monotonic Tensile Test and Correlation between the Yield Strength and Thermoelasto-Plastic Limit Stress on the Example of Aluminum Alloys.

This paper presents an attempt to generalize the description of the course of specimen temperature changes during the tensile test and to connect the value of the thermoelasto-plastic limit stress with the value of a clear (physical) or proof strength (offset yield strength) on the example of tests of the following aluminum alloy sheets used in Poland for airplane structures: 2024-T3 and D16 in three grades: D16ATV, D16CzATV, and D16UTV. A thermographic camera was used for specimen surface temperature measurement during the tensile test. The Portevine–Le Chatelier effect (the so-called PLC effect) was observed for tests of specimens cut from sheet plates, which was strongly reflected in the temperature fluctuations. The course of temperature change during tensile tests was divided into four characteristic stages related to the occurrence of a clear or offset yield strength. It was found that if there is a clear yield strength, the value of the thermoelasto-plastic limit stress was greater than this yield strength. If there was an offset yield strength, the value of the thermoelasto-plastic limit stress was lower than this yield strength. The differences in the aforementioned values of individual yield strengths did not exceed several percent. Thus, it can be concluded that the thermoelasto-plastic limit stress determined on the basis of the course of specimen temperature changes during the tensile test is well correlated with the value of the yield strength of the material.

Fatigue Characterization of SiC/SiC Ceramic Matrix Composites in Combustion Environment

Abstract Fatigue behavior of woven melt infiltrated (MI) SiC/SiC ceramic matrix composites (CMCs) was investigated under a tension–tension fatigue condition in a combustion environment. A special experimental facility is designed to subject the CMCs under simultaneous mechanical and combustion conditions which is more representative of some conditions experienced by the hot section components of a jet engine. The MI SiC/SiC CMCs considered in this study consists of a SiC matrix densified with liquid Si infiltration, BN interphase, and reinforced with two different fibers, namely, Hi–Nicalon type S and Tyranno SA fibers. A high velocity oxygen fuel (HVOF) gun is used to create the representative combustion condition and a horizontal hydraulic MTS machine to apply the mechanical loading. Several fatigue tests were conducted at different stress levels with a stress ratio of 0.1, frequency of 1 Hz, and the specimen surface temperature at 1200 °C. Similar tests were conducted in an isothermal furnace condition at 1200 °C for comparison. Electrical resistance (ER) was used to monitor the tests. A reduction in the fatigue life was observed for the two MI systems under combustion conditions in comparison to the isothermal furnace condition at the same applied stress level. This is attributed to the presence of harsh combustion environment present in the burner rig. ER showed some promising results in monitoring the temperature and detecting damage in the specimen. Runout condition was set as 24 H (86400 cycles) in burner rig and 100 H (360000 cycles) in furnace environment. Specimens that achieved the runout condition were subsequently tested under monotonic tension testing at room temperature after cooldown to evaluate the residual properties. Residual strength results showed a significant strength reduction in both the furnace and burner rig environments. Post-test microscopy was conducted on the fracture surfaces of the failed specimens to understand the oxidation behavior and damage mechanisms.