Mechanical properties of unmodified and montmorillonite-modified epoxy compounds. Part I: compression test

The aim of the article was to determine the compressive strength and compressive strain of an unmodified and a modified epoxy compounds containing a montmorillonite filler, as well as to determine the effect of temperature and an aging time on the mechanical parameters of the considered epoxy compounds. The subject of the research was both the unmodified and the modified adhesive compounds. The unmodified epoxy compounds were made in four variants, which included the epoxy resins based on a bisphenol A as well as the curing agents: a triethylenetetramine and a polyamide curing agent. The modified compounds containing the montmorillonite filler, were also made in four variants. The samples were subjected in a thermal chamber at 80 °C for 1 and 2 months and in a thermal shock chamber in the temperature range from − 40 °C to 80 °C for 1 and 2 months. The reference samples were seasoned at room temperature 20–25 °C. The epoxy compounds samples were subjected to the compression strength tests in accordance with ISO 604 standard. The compressive strength is influenced by the environment and temperature, the aging time and the presence of the modifying agent. The epoxy compounds subjected at elevated or variable temperatures have higher compressive strength than the reference epoxy compounds. The operation of the climatic chamber or the thermal shock chamber makes the samples more deformable than the reference samples.

Experimental Study of Mechanical Properties of Epoxy Compounds Modified with Calcium Carbonate and Carbon after Hygrothermal Exposure

The objective of this paper is to analyze the effects of hygrothermal exposure on the mechanical properties of epoxy compounds modified with calcium carbonate or carbon fillers. In addition, comparative tests were carried out with the same parameters as hygrothermal exposure, but the epoxy compounds were additionally exposed to thermal shocks. The analysis used cylindrical specimens produced from two different epoxy compounds. The specimens were fabricated from compounds of epoxy resins, based on Bisphenol A (one mixture modified, one unmodified) and a polyamide curing agent. Some of the epoxy compounds were modified with calcium carbonate (CaCO3). The remainder were modified with activated carbon (C). Each modifying agent, or filler, was added at a rate of 1 g, 2 g, or 3 g per 100 g of epoxy resin. The effect of the hygrothermal exposure (82 °C temperature and 95% RH humidity) was examined. The effects of thermal shocks, achieved by cycling between 82 °C and −40 °C, on selected mechanical properties of the filler-modified epoxy compounds were investigated. Strength tests were carried out on the cured epoxy compound specimens to determine the shear strength, compression modulus, and compressive strain. The analysis of the results led to the conclusion that the type of tested epoxy compounds and the quantity and type of filler determine the effects of climate chamber aging and thermal shock chamber processing on the compressive strength for the tested epoxy compounds. The different filler quantities, 1–3 g of calcium carbonate (CaCO3) or activated carbon (C), determined the strength parameters, with results varying from the reference compounds and the compounds exposure in the climate chamber and thermal shock chamber. The epoxy compounds which contained unmodified epoxy resin achieved a higher strength performance than the epoxy compounds made with modified epoxy resin. In most instances, the epoxy compounds modified with CaCO3 had a higher compressive strength than the epoxy compounds modified with C (activated carbon).

Investigation of the Effect of Operational Factors on Conveyor Belt Mechanical Properties

This paper aims to present the effect of specific operational factors (temperature and humidity) on the selected mechanical properties of a conveyor belt. The tests were conducted in a climatic chamber, simulating the effect of both minus and plus temperatures −30 °C to 80 °C (243 K to 353 K) at specific humidity, and in a thermal shock chamber where a varying number of ageing cycles was applied for a specific range of thermal shocks. Six different tests in the climatic chamber and four different tests in a thermal shock chamber were conducted. The results of the climatic chamber tests demonstrate that many strength parameters have undesired values at a temperature of 10 °C (283 K) and 80 °C (353 K) at a relative humidity of 80%. Interestingly, the results revealed that tensile strength, tensile modulus and yield strength are higher at below 0 °C temperature than at above 0 °C temperature. For example, comparing the temperature −30 °C (243 K) and +30 °C (303 K) obtained a difference of tensile modulus of nearly 10%, and comparing the temperature −30 °C (243 K) and +10 °C (283 K) the differences were 22%.

Effect of a Notch on Impact Resistance of the Epidian 57/Z1 Epoxy Material after "Thermal Shock"

Adhesive bonding is increasingly being applied as structural joining technique in highly reliable machines and appliances operating in the circumstances of variable thermomechanical loads.The manufactured specimens of the Epidian 57/Z-1 epoxy material had been subjected to cyclic thermal loading, with respect to a defined program, in a thermal shock chamber within a temperature range of ‑40°C to +60°C for 200 cycles. The accepted temperature range was typical for machinery maintenance, including the aircraft.The aim of the research was first of all determination of thermal load (fatigue), as well as the presence of notch effect on the resistance to fracture.A significant measure of the adhesive bonds quality is the repeatability of the strength examination results, both in the summary and long lasting tests. It is often more important criterion for the adhesive joint selection than higher strength of the joints using the particular adhesive.The obtained results of the conducted research have been elaborated statistically with respect to the appropriate scientific standards.

5‐HT depletion, but not 5‐HT1A antagonist, prevents the anxiolytic‐like effect of citalopram in rat contextual conditioned fear stress model

ObjectiveSelective serotonin reuptake inhibitors (SSRIs) have been widely used in the treatment of most anxiety disorders. In this study, to clarify the mechanism of the anxiolytic effect, we investigated the mechanism underlying the effect of the SSRI citalopram on rat contextual conditioned fear stress (CFS), an animal model of anxiety.MethodsRats individually received footshocks in a shock chamber. More than 1 day later, they were given citalopram and/or dl‐p‐chlorophenylalanine (PCPA), various subtype‐selective serotonin (5‐HT) receptor antagonists: the 5‐HT1A receptor antagonist WAY 100635, the 5‐HT2A receptor antagonist MDL 100907, the 5‐HT2C receptor antagonist SB 242084, the 5‐HT3 receptor antagonist tropisetron, the 5‐HT4 receptor antagonist GR 125487, the 5‐HT6 receptor antagonist SB 258585 or the 5‐HT7 receptor antagonist SB 269970. After drug administration, freezing behaviour, which was used as an index of anxiety, was analysed in the same shock chamber without shocks.ResultsCitalopram dose dependently reduced conditioned freezing behaviour. The anxiolytic‐like effect of citalopram was prevented completely by pretreatment with the 5‐HT‐depleting agent PCPA, but not by the 5‐HT1A receptor antagonist WAY 100635. Furthermore, none of the subtype‐selective 5‐HT receptor antagonists significantly affected conditioned freezing or affected the anxiolytic‐like effect of citalopram.ConclusionThe anxiolytic‐like effect of citalopram in contextual CFS model depends on 5‐HT availability. In addition, contextual CFS model is suggested to be completely different from conventional anxiety models in neural mechanism or manners of serotonergic involvement. However, further studies are needed to identify the pharmacological mechanisms responsible for the anxiolytic‐like effect of citalopram.

Failure Analysis of Thermally Shocked NiCr Films on Mn-Ni-Co Spinel Oxide Substrates

NiCr films were thermally evaporated on the Mn-Ni-Co-O thick-film substrates. The NiCr/Mn-Ni-Co-O bi-layer systems were tested in a thermal shock chamber with three temperature differences of 150, 175 and 200°C. The systems were considered to have failed when the sheet resistance of NiCr films changed by 30% relative to an initial value. As the cyclic repetition of thermal shock increased, the sheet resistance of NiCr coatings increased. The Coffin-Manson equation was applied to the failure mechanism of cracking of NiCr coatings and the SEM observation of cracks and delamination in NiCr coatings due to thermal cycling agreed well with the failure mechanism.

Paper 2: Accuracy in Cylinder Pressure Measurement

The paper commences with a definition of the requirements of cylinder pressure measurements for (1) general engine development work, (2) frequency spectrum analysis in engine noise investigation, and (3) thermodynamics and combustion analysis. Methods for the determination of the frequency response of cylinder pressure transducers are then treated both theoretically and experimentally. For the continuous recording type of transducer a shock chamber technique is used. For the balanced pressure type of pick-up a comparison with a continuous recording type, of known frequency response, is made. These techniques do not completely simulate engine conditions and comparisons of the two types of pressure transducers were made dynamically under engine conditions. The results showed that all the continuous recording types of pressure transducer so far tested were sensitive to transient heat transfer owing to combustion. A rig was therefore developed to simulate such conditions outside the engine. Detailed descriptions are given of examples of both types of pressure transducer as developed at C.A.V. The method of recording timing marks is presented in some detail and the advantage of the ‘closed circuit’ magnetic type of degree pick-up is described.