Aging effects of aqueous environment on mechanical properties of calcium carbonate-modified epoxy resin

The purpose of this study was to assess the effects of different aqueous environments (i.e., demineralised, distilled and spring water) on the mechanical properties of a cold-cured bisphenolic epoxy resin modified with the addition of calcium carbonate filler, typically employed as structural adhesive. The parameters selected for the analysis have been; the kind of curing agent employed to cure the epoxy resin at ambient temperature (i.e., Mannich base and triethylenetetramine); the load of calcium carbonate added to liquid epoxy (i.e., from 1 to 3 g per 100 g of resin) and; the duration of the exposure to the different aging conditions (i.e., from 1 to 10 months). Cylindrical specimens of calcium carbonate-modified epoxy systems were tested in compression mode, before and after each of the aging regimes. The effect of the selected curing agents is very small, and they are both suitable for a cure at ambient temperature, on the unfilled epoxy on compressive maximum strength and strain at break; the choice of the hardener affects instead the compressive modulus. The CaCO3 amount was demonstrated to have a significant effect on the mechanical characteristics of un-aged epoxy systems, leading to growth in compressive modulus and maximum strength with reductions in strain at break. Generally speaking, the aging time noticeably affects the compressive properties of calcium carbonate-modified epoxies while almost negligible is the kind of water employed in each exposure regime. Notwithstanding the adverse effects of an aqueous environment on compressive mechanical properties of CaCO3-filled epoxies, these systems keep compressive modulus and maximum strength greater than, and close to, respectively, the same characteristics measured on unaged unfilled control epoxies, demonstrating the positive effect of the addition of this kind of filler to epoxy-based structural adhesives, especially with the addition of 2 and 3 g of CaCO3 per 100 g resin. The results obtained in this study demonstrated that it is possible to contrast the detrimental effects observed in cold-cured epoxy-based structural adhesives due to their aging in water upon the addition of limited amounts (particularly at 2 and 3 g per 100 g resin) of a cheap CaCO3 filler

Research on influence of cyclic degradation process on changes of structural adhesive bonds mechanical properties

ArticleThe paper deals with an influence of a cyclic degradation process on changes of a shear tensile strength of single lap-shear adhesive bonds and their elongation according to ČSN EN ISO 9142. Five one-component structural adhesives used in a construction of car body works were used within the research. The degradation of adhesive bonds is a significant factor which influences a quality and a service life of adhesive bonds exposed to environment. A main requirement in production companies is not only reaching satisfactory initial mechanical properties but namely ensuring a reliability and a safety of adhesive bonds during their usage. These reasons show a great importance of adhesive bonds tests either directly in the operating environment or by a simulation of operating conditions in laboratories. The degradation process of adhesive bonds worsens mechanical properties of not only the bond itself but also of the bonded material. This process is progressing and it is usually permanent and irreversible. It is a change of mechanical and physical properties which can endanger a safety and a reliability of parts, prospectively of the whole equipment. It can leads up to a complete failure of its function in the extreme case. A temperature, a moisture, a direct contact with water and chemicals or an atmospheric corrosion belong among the most serious degradation agents. It is important to take into regard time of the processes influence at the same time which can act either independently or concurrently when their effects grow stronger. From that reason the adhesive bonds were exposed to the cyclic degradation process according to the standard ČSN EN ISO 9142. Subsequently, the adhesive bonds mechanical properties were tested on universal testing machine and by means of SEM analysis (TESCAN MIRA 3). Results of mechanical tests proved a fall of the shear tensile strength of single lap-shear adhesive bonds after 42 cycles of the degradation process of 12.8 to 21.7%. The bond strength fall was gradual and it showed a linear trend at some adhesives. Other adhesives showed a significant fall after the exposition to the degradation process after which the strength fall stabilized

Search for shower's duplicates at the IAU MDC. Methods and general results

Observers submit both new and known meteor shower parameters to the database of the IAU Meteor Data Center (MDC). It may happen that a new observation of an already known meteor shower is submitted as a discovery of a new shower. Then, a duplicate shower appears in the MDC. On the other hand, the observers may provide data which, in their opinion, is another set of parameters of an already existing shower. However, if this is not true, we can talk about a shower that is a false-duplicate of a known meteor shower. We aim to develop a method for objective detection of duplicates among meteor showers and apply it to the MDC. The method will also enable us to verify whether various sets of parameters of the same shower are compatible and, thus, reveal the false-duplicates. We suggest two methods based on cluster analyses and two similarity functions among geocentric and heliocentric shower parameters collected in the MDC. 8 new showers represented by two or more parameter sets were discovered. 31 times there was full agreement between our results and those reported in the MDC. 23 times the same duplicates as given in the MDC, were found only by one method. We found 27 multi-solution showers for which the number of the same duplicates found by both method is close to the corresponding number in the MDC database. However for 60 multi-solution showers listed in the MDC no duplicates were found by any of the applied methods. The obtained results confirmed the effectiveness of the proposed approach of identifying duplicates. We have shown that in order to detect and verify duplicate meteor showers, it is possible to apply the objective proposal instead of the subjective approach used so far

The influence of selected factors on the strenght of wood adhesive joints

This paper examines the effect of selected factors on the wood bonded joint strength. The structural factor under scrutiny was the geometry of the surface area; however, other major dimensions of adherends were compared as well. The tests were per-formed on 6 joint types: butt, v-shaped, interlocking, scarf, tongue & groove, and single lap joints, which were formed on two types of substrate materials – pine and oak wood, and adhesively bonded. The joints were bonded with Prefere 6312 wood adhesive and Loctite 3430 two-component epoxy adhesive. Strength testing of the joints was performed on Zwick/Roell Z150 material testing machine, according to DIN EN 1465 standard. The results obtained from the tests indicate that bonded joints of oak wood exhibit higher strength properties than those of pine wood adherends, which was confirmed in nearly all strength tests

Showers with both northern and southern solutions

Meteoroids of a low-inclination stream hit the Earth arriving from a direction near the ecliptic. The radiant area of stream like this is often divided into two parts: one is situated northward and the other southward of the ecliptic. In other words, two showers are caused by such a stream. Well-known examples of such showers are the Northern Taurids, #17, and Southern Taurids, #2, or the Northern $\delta$-Aquariids, #26, and Southern $\delta$-Aquariids, #5. While the meteoroids of the northern shower collide with the Earth in the descending node, those of the southern shower collide with our planet in the ascending node of their orbits. Because of this circumstance and tradition, the northern and southern showers must be distinguished. Unfortunately, this is not always the case with meteor showers listed in the IAU Meteor Data Center (MDC). For the same shower, some authors reported a set of its mean parameters corresponding to the northern shower and other authors to the southern shower. We found eleven such cases in the MDC. In this paper, we propose corrections of these mis-identifications.Comment: Submitted: Planetary and Space Scienc

New Nomenclature Rules for Meteor Showers Adopted

The Shower Database (SD) of the Meteor Data Center (MDC) had been operating on the basis of stream-naming rules which were too complex and insufficiently precise for 15 years. With a gradual increase in the number of discovered meteor showers, the procedure for submitting new showers to the database and naming them lead to situations that were inconsistent with the fundamental role of the SD - the disambiguation of stream names in the scientific literature. Our aim is to simplify the meteor shower nomenclature rules. We propose a much simpler set of meteor shower nomenclature rules, based on a two-stage approach, similar to those used in the case of asteroids. The first stage applies to a new shower just after its discovery. The second stage concerns the repeatedly observed shower, the existence of which no longer raises any doubts. Our proposed new procedure was approved by a vote of the commission F1 of the IAU in July 2022.Comment: Submitted to: New Astronomy Review

Modification of the Shower Database of the IAU Meteor Data Center

The Shower Database (SD) of the Meteor Data Center (MDC) has been operating for 15 years and is used by the entire community of meteor astronomers. It contains meteor showers categorised in individual lists on the basis of their status. Since the inception of the SD, no objective rules for moving showers between individual lists have been established. The content of the SD has not yet been checked for the correctness of the meteor data contained therein. Our aims are (1) to formulate criteria for nominating meteor showers for established status, (2) to improve the rules for the removal of showers, (3) to verify and enhance the content of the SD, and (4) to improve the user area of the MDC SD. The criteria for moving showers from the Working list to the Lists of established or removed Showers were generated using an empirical evaluation of their impact on the registered showers. The correctness of the parameters of each stream included in the SD was checked by comparing them with the values given in the source publications. We developed a set of criteria for nominating showers to be established. We objectified rules for the temporary and permanent removal of meteor showers from the Working list. Both of our proposed new procedures were approved by a vote of the commission F1 of the IAU in July 2022. We verified more than $1350$ data records of the MDC SD and introduced $\sim$1700 corrections. We included new parameters for shower characterisation. As a result of our verification procedure, 117 showers have been moved to the List of removed showers. As of October 2022, the SD contains 923 showers, 110 of which are in the List of established Showers and 813 are in the Working list. We also improved the user area of the SD and added a simple tool to allow a quick check of the similarity of a new shower to those in the database