Temperature Changes Of Specimens Research Articles

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.

Heat transfer and mechanical properties of wood-plastic composites filled with flake graphite

Wood plastic composites (WPCs) are a new generation of green composites which can come mostly from recycled materials. The addition of the flake graphite (FG) fillers has a significant influence on the properties of WPCs and this study focuses on the heat transfer and mechanical properties of WPCs. The thermal conductivity increases with the increase of addition amount of FG and decreases with the increase of temperature. By comparing the temperature changes of specimens during heating and cooling process, WPCs with higher FG contents presents higher average equilibrium temperature. The WPCs adding FG fillers obtain a greater flexural modulus but a lower flexural strength due to the heterogeneous distribution of the stress. In general, the mechanical properties of WPCs decrease slightly with increasing content of the FG.

Thermal and mechanical properties of wood‐plastic composites filled with multiwalled carbon nanotubes

ABSTRACTWood plastic composites (WPCs) are a new generation of green composites which can come mostly from recycled materials. This study focuses on the thermal conductivity and mechanical properties of WPCs filled multiwalled carbon nanotubes (MWCNTs). The thermal conductivity increases with increasing amount of MWCNTs and decreases with increasing temperature. By comparing the temperature changes of specimens during heating and cooling processes, WPCs with higher MWCNTs contents presents higher average temperature when heated until equilibrium temperature. From differential scanning calorimeter test, the melting temperatures of MWNTs reinforced WPCs change slightly, but the crystallinity is reduced with the increasing amount of MWCNTs. Based on a series of laboratory experiments carried out to investigate the mechanical performance, it can be concluded that the addition of the MWCNTs decreases the mechanical properties of WPCs due to the decohesion between thermoplastic matrix and MWCNTs particles under stress. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46308.

Infrared thermographic analysis of shape memory polymer during cyclic loading

In this paper we present the effects of thermomechanical couplings occurring in polyurethane shape memory polymer subjected to cyclic tensile loadings conducted at various strain rates. Stress–strain characteristics were elaborated using a quasistatic testing machine, whereas the specimen temperature changes accompanying the deformation process were obtained with an infrared camera. We demonstrate a tight correlation between the mechanical and thermal results within the initial loading stage. The polymer thermomechanical behaviour in four subsequent loading-unloading cycles and the influence of the strain rate on the stress and the related temperature changes were also examined. In the range of elastic deformation the specimen temperature drops below the initial level due to thermoelastic effect whereas at the higher strains the temperature always increased, due to the dissipative deformation mechanisms. The difference in the characteristics of the specimen temperature has been applied to determine a limit of the polymer reversible deformation and analyzed for various strain rates. It was shown that at the higher strain rates higher values of the stress and temperature changes are obtained, which are related to higher values of the polymer yield points. During the cyclic loading a significant difference between the first and the second cycle was observed. The subsequent loading-unloading cycles demonstrated similar sharply shaped stress and temperature profiles and gradually decrease in values.

Temperature Changes Induced by the Portevin-Le Châtelier (PLC) Effect during Tensile Test Based on the Example of CuZn37 Brass

This paper presents results of research on PLC effect in CuZn37 brass. A thermographic camera was applied in the tests for determining surface temperature distributions of the tested specimens during tension. Spatial-temporal diagrams were prepared on the basis of those distributions. The tests were performed at two strain rates. No significant difference in the tension curve course depending on the above rate was found. Significant difference was observedas regards the course of specimen temperature changes. Increased frequency of the permanent strain wave propagating along the specimen centerline was observed together with the increase of the wave propagation speed for the higher strain rate. Simultaneous initiation of two propagating waves in opposite directions was observed in case of the higher strain rate.

Development of Stress-Induced Martensitic Transformation in TiNi Shape Memory Alloy

TiNi shape memory alloy (SMA) was subjected to tension at strain-controlled test on quasistatic testing machine. The nucleation, development, and saturation of the stress-induced martensitic transformation were investigated, taking into account the obtained dependency of mechanical parameters and the specimen temperature changes measured by an infrared camera (IR). Three kinds of data obtained by the IR system were analyzed: the temperature distribution on the SMA sample surface, the temperature changes derived as average from the chosen sample area, and the temperature profiles obtained along the sample length. The temperature distribution shows nucleation of the transformation process and a creation of the transformation bands. The average temperature reflects the effects of thermomechanical coupling, accompanying exothermic martensitic forward and endothermic reverse transformation. The temperature profiles revealed the temperature difference between the band and the rest of the sample. The experimental results were supported with finite element method numerical analysis (FEM). The FEM software components for structural and heat transfer problems, coupled in partitioned approach, were used for thermomechanical analysis.

Development of transformation bands in TiNi SMA for various stress and strain rates studied by a fast and sensitive infrared camera

TiNi shape memory alloy (SMA) was subjected to tension at various strain rates for stress- and strain-controlled tests. The nucleation, development and saturation of the stress-induced martensitic transformation were investigated, based on the specimen temperature changes, measured by a fast and sensitive infrared camera. It was found that the initial, macroscopically homogeneous phase transformation occurs at the same stress level for all strain rates applied, regardless of the loading manner, while the stress of the localized transformation increases with the strain rate. At higher strain rate, a more dynamic course of the transformation process was observed, revealed in the creation of numerous fine transformation bands. An inflection point was noticed on the stress–strain curve, dividing the transformation range into two stages: the first heterogeneous, where transformation bands nucleate and evolve throughout the sample; the second, where the bands overlap, related to significant temperature increase and an upswing region of the curve. In the final part of the SMA loading a decrease of the average sample temperature revealed the saturation stage of the transformation. It was also observed that nucleation of the localized martensitic forward transformation takes place in the weakest area of the sample in both approaches, whereas the reverse transformation always initiates in its central part.

ダイカスト用 Zn-Al 合金の大気腐食特性に及ぼす第三元素添加の効果

The effects of third element addition on the atmospheric corrosion resistance of zinc die-cast alloys were investigated by using the cyclic wet and dry test which simulated a diurnal change in specimen temperature and relative humidity in an actual outdoor environment with a constant dew point of 301 K. The amount of chloride ion deposition on the specimen surface was adjusted to 1.0×10-3 g·m-2 by the formation of a uniform layer of diluted synthetic sea water. The addition of magnesium (Mg) improved the corrosion resistance of zinc alloys, while the addition of nickel (Ni) degraded the corrosion resistance. X-ray photoelectron spectroscopy measurements indicated that corrosion products formed on Mg-added alloys contained Mg compounds such as oxide, hydroxide, and carbonate. Electrochemical polarization curves of as-polished specimens indicated that the addition of Mg has little effect on anodic and cathodic reaction rates. On the contrary, the addition of Ni or Ti promoted cathodic reaction. The polarization curves measured on specimens after 1 cycle of the cyclic corrosion test indicated that the corrosion products formed on Mg-containing alloys leaded to anodic passivation and inhibited cathodic reaction, while those on Ni-containing alloys accelerated cathodic reaction. Scanning electron microscopic observation on specimens after 1 cycle of the cyclic corrosion test showed that Mg-containing alloys had smooth and uniform surfaces with dense corrosion products, while Ni- or Ti-containing alloys had rough surfaces. It is concluded that the formation of thin and dense corrosion product layer is responsible for the high corrosion resistance of Mg-containing alloys.

ダイカスト用亜鉛合金の大気腐食特性に及ぼす合金元素の影響

The effect of alloying elements on the atmospheric corrosion behavior of zinc die-casting alloys was investigated using the cyclic wet and dry test which simulated a diurnal change in specimen temperature and relative humidity in an actual outdoor environment. The deposition amount of chloride ions on the specimen surface was adjusted to 1.0×10-3 and 1.0 g•m-2 by forming of a uniform layer of diluted synthetic seawater. The addition of aluminum and mischmetal (MM) improved the corrosion resistance of zinc die-casting alloys, while that of Cu degraded the corrosion resistance. Polarization measurements indicated that Cu addition promotes the reduction reaction of dissolved oxygen. Corrosion products formed on Cu-containing specimens also promoted the cathodic reaction. On the contrary, the corrosion products on Al-containing and MM-containing alloys had the ability to suppress the anodic reaction. The value of average corrosion depth and the composition of corrosion products in the accelerated corrosion test were compared to those obtained by atmospheric exposure tests. It was concluded that the cyclic wet and dry test, in which diluted synthetic seawater is used as a test solution, is appropriate for an accelerated atmospheric corrosion test for zinc alloys.

High Resolution Magnetic Resonance Imaging of Excised Atherosclerotic Carotid Tissue: The Effects of Specimen Temperature on Image Contrast

Previous Magnetic Resonance (MR) studies of carotid endarterectomy (CEA) specimens have been directed at interpreting image contrast to determine plaque composition and stability. Such studies may give misleading results since it is believed that the acquired MR data is affected by the conditions used to store the excised tissue. This has been investigated in a high-resolution imaging study of the changes in contrast occurring with a change in specimen temperature. MR images were acquired from 20 CEA specimens. The initial MR examination was made within four hours of excision in tissue maintained and imaged at body temperature. Specimens were subsequently cooled and then re-examined at different times. The MR data was interpreted by comparison with histology obtained from equivalent sections. With the exception of signals arising from blood, changes in MR image contrast occurring in the 24-hour period after the CEA were relatively slight. Plaque lipid T2-weighted image intensity was initially relatively hyperintense in some samples and decreased with time on cooling reflecting a decrease in the lipid transverse (T2) relaxation time. High-resolution imaging allowed a detailed description of plaque calcification and showed that clot retraction was probably responsible for the marked change in the distribution of signals assigned to intraluminal blood. The use of high-resolution MR imaging to examine freshly excised specimens at body temperature showed previously unreported image features. This is important in the design of in vivo MR studies directed at assessing plaque stability by identifying the composition of the atheromatous tissue.

Effect of internal heating during hot compression on the stress-strain behavior of alloy 304L

The temperature change due to the conversion of mechanical deformation to internal heat and its effect on the as-measured stress-strain behavior of alloy 304L was investigated by means of initially isothermal (compression specimen, dies, and environment at same temperature at initiation of test), constant strain rate, uniaxial compression of laboratory-sized cylindrical specimens. Strain rate was varied in the range 0.01 to 1 s−1, where the thermal state of the test specimen varied from nearly isothermal to nearly adiabatic, respectively. Specimens were deformed in the temperature range of 750 °C to 1150 °C to a strain of 1. The change in specimen temperature with applied strain was calculatedvia finite-element analysis (FEA) from the asmeasured stress-strain data. Selected predictions were confirmed with embedded thermocouples to verify the model employed. Temperature was found to increase monotonically with strain at a strain rate of 1 s-1, consistent with what is theoretically expected for the adiabatic case. At the 0.1 and 0.01 s-1 rates, the sample temperature initially increased, peaked, and then decreased as the sample thinned and the contact area between the sample and the cooler dies increased. As-measured stress was corrected for softening associated with deformational heating by interpolation between the various instantaneous stress-temperature behaviors. The resulting isothermal flow data are compared to those predicted by a conventional method that employs an empirical estimate of the heat retention efficiency of the test specimen, assumed dependent on strain rate but independent of strain, to reduce the increase in temperature calculated for the adiabatic case. Differences between the calculated isothermal stress-strain data from the two methods are discussed. Values for the apparent activation energy of deformation and the strain to the peak in the flow curve, which is associated with the onset of dynamic recrystallization, determined from isothermal stress-strain data differed significantly from those obtained from the as-measured compression test data.

Anomalous Transmission of Thermally Scattered X-Rays in Germanium Crystal

Strong excess lines were observed across the 111 diffuse spots of CuK α and CuK β radiations in the Bragg arrangement and across the 220 diffuse spot of CuK α radiation in the Laue arrangement on photographs of germanium crystals taken by using unfiltered radiation from copper target operated at accelerating voltage 30 kV. Crystal orientation dependence of the excess line and intensity variation of the excess line similar to that of thermal diffuse scattering with change in specimen temperature strongly suggest that the excess line is caused by anomalous transmission of the thermally scattered characteristic X-rays in the perfect crystal.

Accuracy of the confirmatory diagnosis of tuberculosis

1. 1. The accuracy of the properly performed tuberculin skin test beginning with 1–1000 O.T. and followed by 1–100 O.T.), if negative with both dilutions, is so great in ruling out tuberculosis that it becomes the keystone in the diagnosis of the disease, since 59 per cent of patients even with roentgenographic changes sufficient (in miniature films) to arouse suspicion of tuberculosis have negative Mantoux tests. 2. 2. A positive Mantoux test in a child less than six years of age indicates active primary disease. A positive Mantoux test in a patient over six years of age indicates a prior primary infection, and if disease is present anywhere in the body, tuberculosis must be ruled out. 3. 3. In order to recover tubercle bacilli from lesions, repeated specimens cultured on two different media are required because the tubercle bacilli may not be present in sputum or gastric cultures every day and may grow better in one medium than another even though both will support tubercle bacilli in the positive control. 4. 4. Lowenstein's and Petragnani's media are complementary and equally effective in outpatient cultures. Petragnani's medium gives a higher percentage of positive results on inpatient cultures and a lower percentage of contaminations. 5. 5. A single positive smear or culture is sufficient reason to hospitalize a patient and to begin treatment. 6. 6. Many factors influence the recovery of tubercule bacilli: (a) total number of tubercle bacilli in the specimen; (b) the digestant material kills 80 per cent of the viable tubercle bacilli; (c) pH above or below 7 may rapidly kill the tubercle bacilli; (d) temperature changes of specimens above or below 30 °c. decrease the number of viable tubercle bacilli; (e) by-products of vitamin C in urine are bactericidal; and (f) antibiotics inhibit the growth of tubercle bacilli on culture media. 7. 7. Contamination is a major problem in culture work, the highest contamination occurring in outpatient specimens, drainage from sinus tracts, and aspirated fluids. The lowest contamination rate occurs with inpatient sputums. 8. 8. Using three specimens cultured on two different media, we have recovered tubercle bacilli from 22.5 per cent of primary cases, 94 per cent of patients with minimal tuberculosis, 95 per cent of patients with moderately advanced pulmonary tuberculosis, and 95 per cent of patients with far-advanced tuberculosis. 9. 9. The erythrocyte sedimentation rate is of no value in the diagnosis of active tuberculosis since we found it to be normal in over one-fourth of patients with positive cultures. 10. 10. A pathologic diagnosis of tuberculosis was not returned in thirty of 189 specimens sent even though one or more positive cultures had been obtained from each patient. There was disagreement between culture and pathologic diagnosis in 15.8 per cent of these cases. 11. 11. Since the advent of combined chemotherapy all our tuberculosis deaths occurred in patients with advanced disease, either pulmonary or extrapulmonary, which was present on admission; there were no deaths from primary or minimal pulmonary disease. 12. 12. When one realizes the difficulties in recovering tubercle bacilli and the ways in which these procedures can go amiss, the value of short-term work-up with three gastric specimens that can be cultured immediately by qualified technicians using culture media that grow tubercle bacilli, becomes of increasing importance. If the bacilli are dead on arrival, or viable tubercle bacilli are planted on culture media that will not support them, negative results mean nothing. 13. 13. Without the three-day period of hospitalization during which three gastric specimens are cultured, the diagnosis would have been missed on one-third of the total group; early disease, minimal and moderately advanced pulmonary and primary disease would have been missed most commonly. 14. 14. Tissue examination is of great value in the diagnosis of tuberculosis in extrapulmonary lesions since one-third of this group were diagnosed on the basis of pathology reports; it is of less value in diagnosing moderately and faradvanced disease and of no value in minimal and primary disease since these patients do not require resection nor do they die of the disease. 15. 15. Active tuberculosis is a clinical and not a pathologic diagnosis and it is best substantiated by the recovery of tubercle bacilli from the lesion.