Effects of thawing-induced softening on fracture behaviors of frozen rock

Due to the presence of ice and unfrozen water in pores of frozen rock,the rock fracture behaviors are susceptible to temperature.In this study,the potential thawing-induced softening effects on the fracture behaviors of frozen rock is evaluated by testing the tension fracture toughness(KIC)of frozen rock at different temperatures(i.e.-20℃,-15℃,-12℃,-10℃,-8℃,-6℃,-4℃,-2℃,and 0℃).Acoustic emission(AE)and digital image correlation(DIC)methods are utilized to analyze the microcrack propagation during fracturing.The melting of pore ice is measured using nuclear magnetic resonance(NMR)method.The results indicate that:(1)The KIC of frozen rock decreases moderately between-20℃ and-4℃,and rapidly between-4℃ and 0℃.(2)At-20℃ to-4℃,the fracturing process,deduced from the DIC results at the notch tip,exhibits three stages:elastic deformation,microcrack propagation and microcrack coalescence.However,at-4℃e0℃,only the latter two stages are observed.(3)At-4℃e0℃,the AE activities during fracturing are less than that at-20℃ to-4℃,while more small events are reported.(4)The NMR results demonstrate a reverse variation trend in pore ice content with increasing temperature,that is,a moderate decrease is followed by a sharp decrease and-4℃ is exactly the critical temperature.Next,we interpret the thawing-induced softening effect by linking the evolution in microscopic structure of frozen rock with its macroscopic fracture behaviors as follow:from-20℃ to-4℃,the thickening of the unfrozen water film diminishes the cementation strength between ice and rock skeleton,leading to the decrease in fracture parameters.From-4℃ to 0℃,the cementation effect of ice almost vanishes,and the filling effect of pore ice is reduced significantly,which facilitates microcrack propagation and thus the easier fracture of frozen rocks.

Study on temperature field and settlement of thawing soil under static and dynamic loading

A series of tests were conducted to analyze temperature field distribution and thawing settlement of a thawing soil under static and dynamic loading at various cooling and thawing temperatures. The results demonstrate： （1） the temperature field distribution of the thawing soil was not significantly influenced by the loading form under the tested loading conditions; similar results were obtained for samples at different dynamic loading frequencies and different dynamic loading ampli- tudes, which verified the independence of loading form and temperature field; （2） changed temperature field distributions were found in thawing soil with different cooling and thawing temperatures, and the cooling and thawing temperature of the samples were the main factors affecting their temperature distributions; （3） under the tested conditions, thawing set- tlements were little influenced by the thawing temperature and the dynamic loading frequency; and （4） a linear relation- ship existed between the thawing settlement and the cooling temperature, and a logarithmic function could be used to describe the relationship between the thawing settlement and the loading amplitude.

Effects of Storage Temperature on the Effective Activity of Straw Frozen Semen after Thawing

The aim was to discuss the optimal storage environment and proper insemination time after thawing of 0.25 mL straw frozen semen. Straw frozen semen was thawed at 40 ℃ for 20 s, and then stored at 0 -4 ℃, 14 - 16 ℃, 25 -27 ℃ for 2, 4, 6, 8 and 10 h, respectively. The sperm motility was detected. After thawing, semen was stored at 0 - 4 ℃ and 14 - 16 ℃ for 10 h. Their sperm motilities （0.434 ±0. 016 7 and 0.423 ±0.019 6） had no significant differences （P 〉 0.05） with initial thawing motility （0.441 ± 0.030）. Sperm motility reduced as the storage time prolonged at 25 -27 ℃. Sperm motility after 6 h had signifi- cant differences with that of initial thawing motility （P 〈 O. 05 ）, and sperm motilities after 8 and 10 h showed extremely significant differences （P 〈 0.01 ）. Thus, sperm motility after thawing was still very high after stored at 0 -4 ℃ and 14 - 16 ℃ within 10 h, which met the requirements for insemination. Under this temperature and time ranges, sperm could be carried over long distances, which had small effects on sperm quality and reached the expected insemination effects. However, under the temperature of 25 - 27 ℃, semen should be used for insemination within 6 h after thawing.

Effect of Different Thawing Methods on Post-thaw Motility of Cow Semen in Cryopreservation Straws

The study was to investigate the effects of different thawing temperatures(5,15,40,75,90 ℃) and times(1- 120 s) on properties of post-thaw cow semen by detecting frozen-thawed semen motility,acrosome integrity and tail membrane integrity,further obtaining the optimal thawing method of straw frozen semen from dairy cow. The results showed that(1) Thawing of the straw frozen semen of dairy cow at 75 ℃ for 3 s yielded the highest semen motility,followed by 40 ℃for 20 s,and the least by low temperature 5 ℃ and room temperature 15 ℃ with a semen motility of 0. 3,moreover thawing at high temperature 90 ℃ was not suitable for large scale production due to the difficult control of the temperature;(2) The acrosome intact rate and plasma membrane integrity rate of semens thawed at90 ℃ were remarkably lower than that at 40 ℃ and 75 ℃ significantly(P 【 0. 05),while its semen malformation rate was significantly higher than that at 40 ℃and 75 ℃(P 【 0. 05);(3) The Survival time of semens at 37 ℃ varied largely among different thawing temperature,in detail by 40 ℃ 】 75 ℃ 】 90 ℃. In practice,the thawing method of straw frozen semen of dairy cow should be selected according to the specific circumstance and inseminated immediately,with the recommended condition of thawing at 75 ℃ for 3 s. If the thawed semen could not be inseminated immediately,the thawing should be performed at 20 s for 40 ℃to maintain the motility for a longer term.