Crack growth kinetics in three-dimensional polymethyl methacrylate specimens under internal dynamic loading

Literature data and our experimental results obtained in the studies on crack kinetics in three-dimensional polymethyl methacrylate specimens with an inner cavity made in various shapes over a wide range of loading rates are summarized. Crack initiation and steady propagation velocities as well as energy spent for fracture are found to increase nonlinearly, and the delay time of crack initiation decreases with the rate of internal cavity loading. Subbotin Institute of Geophysics, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 1, pp. 86–94, January–February, 1999.     

Strength of irradiated polymethyl methacrylate

The effect of the form of radiation (reactor and-radiation, X-rays and ultraviolet light) and absorbed energy on the strength of polymethyl methacrylate was studied. It was shown that the strength of this polymer depends in the first place on the size of radiation-induced defects and not on their distribution across the specimen thickness. When therefore the absorbed radiation energy is nonuniformly distributed along the specimen cross section, the mechanical properties of irradiated materials are determined by the radiation dose absorbed by the specimen surface layers.     

Rib formation in the fracture of polymethyl methacrylate

Polymethyl methacrylate was fractured under a variety of loading conditions. Various linear features were observed on fracture surfaces but attention was centered on ribs of torn-out material. Such ribs were formed only in cases where loading conditions resulted in a tensile stress field ahead of the crack tip. Moreover the width of the ribs, and also their spacing, increased as the crack traversed the specimen into zones of increasing tensile stress. These observations, along with previously published data on the dependence of rib spacing on molecular weight and temperature, led to the conclusion that rib formation was due to secondary tensile fractures. These were identified to be showers of microcracks, from side views of the ribs. Fractographic evidence was obtained that the crack accelerates after formation of each rib (i.e. shower) and a “stick-slip” mechanism adopted.     

Statistical aspects in stress crazing of polymethyl methacrylate

The statistical nature of the stress crazing phenomena in polymethyl methacrylate (PMMA) has been investigated. The experiments suggest that the time required for the formation of crazes is an inherent, but statisticaL characteristic of the material itself incorporating a stress depending rate process reflecting to some extent the initial microscopic flaw distribution.

---

Zusammenfassung Es wurde der statistische Charakter der Polyfissuration in Polymethyl-Methacrylat untersucht. Die durchgeführten Versuche deuten darauf hin, daß die fur die Bildung von Poly-Rissen erforderliche Zeit eine dem Material eigene, wenn auch statistische, Eigenschaft ist. Diese Eigenschaft begreift einen spannungsabhängigen Geschwindigkeitsprozeß welcher in einem gewissen Masse die Verteilung der ursprünglichen mikroskopischen Fehlstellen reflektiert.

---

Résumé On a étudié le caractère statistique des phénomènes de polyfissuration dans le metacrylate de polyméthyle.Les essais exécutés laissant entendre que le temps nécessaire à la formation de criques multiples est une caracteristique inhérente, encore que statistique, du matériau lui-même. Cette caractéristique comprend un processus évolutif fonction de la contrainte appliquée, qui traduit, dans une certaine mesure, la distribution des défauts microscopiques présents à l'origine.

     

Diffusion of alcohol-rhodamine 6G in polymethyl methacrylate

Rhodamine 6G (Rh6G) is impregnated in polymethyl methacrylate by concentration difference diffusion method. The diffusion behaviour of ethanoic and methanoic Rh6G in polymethyl methacrylate at temperatures between 35 and 70° C were studied. The following results were obtained: (a) Visually observed sharp boundary, characteristic of Case II transport, during diffusion of alcohol penetrates at a rate of 1.7×10^–6 cm sec^–1 with an activation energy of 23 kcal mol^–1 for ethanol-polymethyl methacrylate system and 1.0×10^–5 cm sec^–1, with 23 kcal mol^–1 for methanol-polymethyl methacrylate, respectively, at 60° C. (b) Diffusion of alcoholic Rh6G in polymethyl methacrylate is greatly hindered since internal stresses exist in the swollen region of the glassy polymer. (c) Diffusion of alcoholic Rh6G in swollen polymethyl methacrylate with equilibrium alcohol concentration followed Fickian kinetics. The diffusion coefficient of Rh6G at 60° C is determined as 5.2×10^–8 cm² sec^–1 with an activation energy of 41 kcal mol^–1 for the wet ethanol-polymethyl methacrylate and 6.1×10^–8 cm² sec^–1, with 34 kcal mol^–1 for the wet methanol-polymethyl methacrylate systems, respectively.     

Investigation of time-to-rupture of polymethyl methacrylate under the combined influence of active liquid media and γ-radiation

Time-to-rupture and creep of polymethyl methacrylate (PMM) under the combined influence of stress, active liquid media, and -radiation were studied. It was shown that time-to-rupture of PMM under these conditions is determined mainly by the influence of the working medium when the absorbed radiation dose is less than about 10 Mrads and that -radiation increases the creep rate of PMM in active liquid media.     

含稀土配合物的甲基丙烯酸甲酯荧光性能研究

含稀土有机配合物的高分子材料综合了稀土材料和高分子材料的优异性能,在制备光学器件方面有广泛的应用前景.本文制备了含铕的噻吩甲酰三氟丙酮(TTA)和二苯甲酰甲烷(DBM)配合物的聚甲基丙烯酸甲酯(PMMA)体系,并考察了配合物含量、配体、小分子掺杂剂和PMMA分子量对体系荧光性能的影响.分析表明要想获得高效发光的稀土配合物高分子体系需要选用对称性较差,含氟取代基较多的配体,并找到合适的配体或小分子掺杂剂的含量,且尽量增大基体的分子量.     

聚甲基丙烯酸甲酯和有机硅材料的复合研究

采用本体聚合的方法,以DMC和甲基丙烯酸甲酯为原料,合成了聚甲基丙烯酸甲酯(PMMA)和聚二甲基硅氧烷(PDMS)的复合粘液。研究了PDMS和MMA的质量比、引发剂AIBN的用量、MMA的聚合温度对复合粘液的影响。采用乌氏黏度计测量出双组分聚合物复合粘液的黏度,并考察了水的用量对硅油黏度的影响及MMA聚合前后共混物黏度的变化情况。结果表明:PDMS和MMA的质量比为6∶1、引发剂AIBN的用量为0.5%、MMA的聚合温度为90℃时,所得复合粘液最稳定;水的用量越大,硅油的黏度越小;水的用量越小,硅油的黏度越大;DMC的聚合时间也能影响硅油的黏度,聚合时间越长,硅油黏度越大;MMA聚合后硅油黏度变大。     

The wave front problem in dynamic photoelasticity

Summary This paper addresses the problem: where to draw the wave front ahead of a fringe pattern in dynamic photoelastic recordings of wave propagations?. The analysis shows that the velocity field of the isochromatic fringes completely determines the location of the wave front.With 5 Figures     

Some effects at ion beam modification of polymethyl methacrylate

Measurements of the sensitivity of polymethyl methacrylate to ion irradiation are presented. The results of these studies show for ion energies (40 keV—1.8 MeV) and for the heavier ions (He⁺, Ar⁺) a higher sensitivity of the resist than in H⁺, electron or X-ray exposures. The measured sensitivity shows a dependence on electronic stopping power. In order to understand this relation an electron excitation spike mechanism is suggested. This mechanism is in accordance with investigations of sputtering rate of PMMA during ion bombardment. The effects of low energy ion induced nuclear reactions in the polymer layer and in masks and wafer are also discussed.     

Effect of polymethyl methacrylate on the grinding of a metal-polymer system

We demonstrate that grinding of metallic turnings in the presence of a destroyable high-molecular-weight compound intensifies the grinding process and contributes to plasticization of the metal. The grinding of the metal-polymer system is accompanied by reduction reactions and desulfurization of the metal being dispersed.