Radka Bálková

This paper investigates the temperature resistance of the load-bearing elements of bonded spruce joints subjected to static tensile shear stress immediately after thermal exposure. Four types of adhesives were used: one-component polyurethane, melamine-urea-formaldehyde, resorcinol-phenol-formaldehyde, and epoxy. The joints were exposed to temperatures of 100, 120, 140, 160, and 180 ° C for 1 and 2 h. To evaluate the influence of temperature on potential wood degradation and its effect on the thermal resistance of bonded joints, the wood itself was subjected to the same conditions and tests as the bonded joints. To isolate the effect of the adhesives, thin films were prepared and their change in stiffness during heating up to 180 ° C was measured using dynamic mechanical analysis. None of the adhesives were fully cured, and post-curing led to an increase in storage modulus and, in the case of MUF and PRF adhesives, significant shrinkage of the films. The strength of all joints decreased with increasing temperature. A continuous decrease was observed in epoxy joints, whereas the other joints exhibited fluctuations in strength. With respect to the decrease in strength, a temperature of 100 ° C already appears to be critical due to glass transition of all adhesives. Adhesives began to show thermal degradation at 140 ° C, which led to an increased incidence of adhesive failure in the joints, however the strength of the wood was also reduced above 140 ° C (a significant drop after 2 h). 1 C PUR-bonded joints exhibited the highest strength at 20 ° C and after thermal exposure, but all adhesive joints except EP demonstrated considerable thermal resistance. A significant effect of the duration of temperature exposure was also demonstrated.

The paper deals with the influence of temperature and cyclic loading on adhesion and transparency of the adhesive joint consisting of soda-lime-silica glass and polycarbonate (PC) bonded with polyurethane (PU) adhesive film. The tested joint represents critical part of transparent armored glass used in vehicles. Dynamic tension creep tests were performed at temperatures to which armored glass is commonly exposed (25, 50, 60, 70, and 80 °C). Sawtooth loading mode was performed to 650 N and the sine loading in the force range 0–1550 N. The aim of the paper was to discover conditions causing delamination of the adhesive joint and glass milky appearance during the use. Delamination of soda-lime-silica glass/PU adhesive interface occurred at 25 °C after load to 1550 N without the change of transparency. Both dynamic and static tension creep tests performed to 400 N led to plastic deformation of PU adhesive at and above 70 °C, in preference at both ends and circumference edges of adhesive joint, and thus, to loss of transparency, but extent of deformation differed. Milky maps observed after sawtooth load to 650 N at 80 °C reflected delaminated areas of highly deformed PU adhesive. Temperature of 70 °C was found out to be the critical parameter being in synergy effect with different thermal expansion of PC and PU adhesive.

One broken and three new polymeric constant-velocity boots (bellows) being a spare part of a constant-velocity joint in two military vehicles were analyzed to identify basic composition and to determine if composition or structure of broken bellows differ. Infrared spectroscopy, differential scanning calorimetry, and thermogravimetry were used for analyses. Bellows for both vehicles are produced from thermoplastic elastomer. Broken bellows is chemically degraded and material just from the fracture is deformed plastically. The life cycle of bellows depends especially on applied stress and temperature (that about −20°C seems to be critical due to crystallization of soft segments).