Polymethylmethacrylate Plates Research Articles

Quasi-track technological dosimetry of narrow electron beams by means of transparent polymers

A simple method is presented for determining the beam electron energy E e within the 4 – 18 MeV range. The method is based on a linear dependence between E e and the distance the plane of the electron beam (EB) input into a sample of polymethylmethacrylate (PMMA) from the remote boundary of the visible traces of internal electric discharge. It is shown that the EB current density profile may be determined by a set of beam tracks in the form of porous mass produced in the irradiated sites of the PMMA plate due to radiation gas evolution.

CONCENTRATORS USING FLUORESCENT SUBSTANCES

In luminescent concentrators - plates of polymethylmethacrylate (PMMA) or other transparent material with a fluorescent compound dispersed within them - incident light is trapped and concentrated by internal reflection, and shifted to a longer wavelength, as it interacts with fluorescent particles. Experience with the use of luminescent concentrators for electricity generation in conjunction with solar cells, in solar heaters, in amplifiers for light intensity, in long-wave converters and in display panels is discussed. Solar energy conversion efficiencies of 4–5% have been obtained in generating systems combining concentrators containing Fluorol 555 or Rhodamin 6G with GaAs solar cells.

Determination and kinetics of platelet adhesion onto material surfaces

An apparatus for the quantitative measurement of platelet adhesion onto a material surface has been constructed by combining a rheoscope with video-image processors. Time courses of the adhesion were obtained by separating the video images of adhered spots from those of flowing platelets in microscopic video frames, and by encoding the area and number of these spots. p]The time course of human platelet adhesion was simulated numerically, on the basis of a simplified kinetic model. In the experiment with a polymethylmethacrylate plate, the rate constant of the platelet adhesion onto the free surface is far smaller than that onto the adhered platelets.

Measurements and simulation of the spatial charge distribution in electron-beam-irradiated polymers

The amount and profile of the charge distribution in a polymethyl methacrylate plate of 7.9-mm thickness were measured after electron beam irradiation. When the plate was irradiated by a beam whose energy was 1 MeV and the total dose was 3 kGy, a spatial charged layer was produced at approximately 2.5 mm from the irradiated side. The maximum charge density was 1.7 μC/cm3 . The charges of the irradiated side decayed faster than the charges which accumulated at positions further away from the irradiated side in the specimen. Computer simulations were carried out to study the charge decay phenomena, assuming that shallow trap levels were created at the irradiated side by the electron beam. The time dependence of the accumulated charge distribution agreed well with the experimental results.

Can natural faults propagate under Mode II conditions?

Various brittle geological structures form from the tip of preexisting joints. Experiments have been carried out to investigate their mechanical origin and to find out whether a planar defect can propagate in its ownplane under mode II geometrical conditions (displacement parallel to the defect plane and perpendicular to the edge) as supposed by the classical rupture mechanics model, and in particular, whether mode II can be an elementary fracture mechanism, which is not clear in the model and has not been experimentally demonstrated. A biaxial loading device (plane strain) allowed direct observation of fracture propagation from an angled slot in plates of Polymethylmethacrylate (PMMA, Altuglas) and sandstone (low and high porosity). Under uniaxial load, mode I propagation of the classical branch fracture occurred in both materials, but its development was inhibited under biaxial loading (low σ3/σ1 ratio). At higher stress/strain levels, shear zones (clearly distinguishable from the branch fracture) developed from the slot tip. In PMMA they consisted of the prograding development of en echelon shallow microcracks formed in mode I and more or less associated with plastic deformation. In sandstone a narrow shear zone propagated in the prolongation of the defect (slowly in the high‐porosity samples and abruptly in the low‐porosity ones) accompanied by conjugate shear fractures. The deformation mechanism was cataclasis, implying tensile (mode I) microfractures. These experiments suggest that mode II cannot exist as an elementary (primary) fracture mechanism but can only be a macroscopic fracture phenomenon which must necessarily involve tensile (mode I) microcrack formation. The latter is linked to stress concentrations in the prolongation of the existing joint. As such mode II initiated shear zones have not been generated in glass, a high density of small defects which can be mobilized under shear stress would seem essential. These ideas can be used to interpret some types of natural faults.

On the elastic properties of depleted refilled solids near percolation

Experiments have been carried out on a polymethyl methacrylate plate in which holes were drilled randomly in order to investigate the elastic behaviour of this depleted system near the percolation threshold. Compression and traction tests were conducted on the plate with both hollow holes and refilled holes. A comparison of the elastic moduli for both situations shows that there is a significant difference between the elastic properties of the structures of 'depleted refilled' solids and the 'depleted' solids. When extrapolated to the case of fractured rocks with small porosity, the authors' results lead to the conjecture that the critical exponent T for the elastic modulus could be closer to De Gennes' universal exponent (t=1.3) than to the exponent for depleted solids (T=3.96).

An Electric Stress-Pulse Technique for The Measurement of Charges in A Plastic Plate Irradiated by an Electron Beam

The distribution profile and quantity of charges in insulators have been studied by various methods, some of them utilizing thermal, mechanical, and electrical stimulations. A new method, incorporating pulse electric stimulations and pulse acoustic detection, is reported here along with preliminary results of the measurement of the amount and approximate distribution profile of charges in electron-beam irradiated polymethyl methacrylate (PMMA) samples. The amount and the mean penetration depth of charges in the sample are obtained from the height of the first acoustic signals produced in response to a HV impulse applied to the sample. A 5 mm thick PMMA plate irradiated with a 1 MeV electrons at 0.5 to 3.0 Mrad was found to trap charges of approximately -0.3 ?C/cm2 at a mean depth of about 2 mm.

Fabrication of microstructures with high aspect ratios and great structural heights by synchrotron radiation lithography, galvanoforming, and plastic moulding (LIGA process)

Under the LIGA process for fabricating microstructures having high aspect ratios and great structural heights, synchrotron radiation lithography produces a primary template which is filled with a metal by electrodeposition. The metallic structure so produced is used as a mould insert for fabricating secondary plastic templates which, in mass production, replace the primary template. This is a report about the status of work performed by the Karlsruhe Nuclear Research Center with the cooperation of Siemens AG and the Fraunhofer Institute for Solid State Technology: By irradiation and development of polymethyl methacrylate (PMMA) plates, primary templates were produced which, for structural heights of several hundred μm, exhibit deviations in critical dimensions of less then some 0.1 μm. The best results were obtained with an X-ray mask consisting of a 25 μm thick beryllium foil and 18 μm thick absorber structures consisting of copper and gold. Practically perfect metallic replicas were obtained by electrodeposition of nickel in the PMMA microstructures and even details in structure of less than 0.1 μm size were reproduced. Moulding was done with a methacrylate-based casting resin with an internal mould release agent. By electrodeposition of nickel in the secondary templates, secondary metal structures were produced which practically do not differ from the primary structures. The LIGA process can be expected to be superior to other methods for fabricating microstructures with high aspect ratios if, in series production of microstructures with complex shapes, stringent requirements are imposed on the resolution, the aspect ratio, the structural height, and the parallelism of the structural walls.

Statistical determination of red cell adhesion to material surface, by varying shear force

A rapid, quantitative method for determining the red cell adhesion to a material surface has been developed, counting the adhered cell number as a function of the applied shear stress in several steps, by means of a rheoscope consisting of an inverted microscope and a transparent cone-plate viscometer. As a typical example, the experimental results on red cell adhesion to a polymethylmethacrylate plate are demonstrated. A theoretical treatment shows that the empirical relation between the number of adhered cells and the applied shear rates is converted to the distribution profile of the adhesive force. Thus the shear stress for 50% dissociation ( τ 50) gives an estimate of the median of the adhesive force. The inhibition of cell adhesion occurs by adding human albumin and fibrinogen, and is quantitatively expressed by the reduction of τ 50 as protein concentrations increase: fibrinogen shows a stronger inhibitory effect than does albumin. The influence of proteins on surface adhesion and on rouleau formation is discussed.

Flexure strength and fracture of polymethylmethacrylate plates

The flexure strength of a polymethylmethacrylate (PMMA) plate is investigated. The plate resting on a ring foundation is subjected to either a quasi-static contact load or the impact load of a spherical projectile. The dynamic fracture load required to fracture the plate specimen is measured to be about 30% higher than the quasi-static fracture load. The piezoelectric accelerometer used to measure the impact load clearly detects the occurrence of fracture as a sudden drop in its signal output. General formulas for the contact between the spherical indenter and the thin plate specimen are obtained to determine the normal contact stress and the critical tensile stress in the plate.The speed of a crack propagating in a PMMA plate specimen under transverse loadings is measured experimentally. Since small in-plane stretching stress is produced in the specimen in the experimental arrangement, the crack speeds measured are small, compared to the limiting crack speed of the material.

Brittle fracture of plates in tension static field radiated by a suddenly stopping crack

Large plates of PMMA (polymethylmethacrylate) containing a long edge crack were subjected to a tensile fracture. The brittle crack was brought to an abrupt stop a pre-determined point. A new technique of crack-arrest, which produces a large discontinuity in fracture toughness while introducing only a small discontinuity in the acoustical properties is described. The strain field emitted during the run-arrest event has been measured in detail using conventional strain gage technique. The fractures take place under a state of nearly plane stress. Consistent with the plane strain analysis of Freund, the field becomes static behind the shear (Rayleigh) wavefront at points lying directly ahead (behind, i.e. on crack face) the arrested cract tip. For points not lying on the crack plane, the analysis predicts that the field is always time-dependent. It is experimentally shown that in a circular region of radius roughly equal to the run-arrest length, the field becomes static (for all practical purposes) behind the shear wavefront emitted by the arrested tip. A fairly strong discontinuity is propagated with the Rayleigh wave emanating from the arrested tip. Finally, the strain field radiated during the run-arrest event is strongly angle-dependent: loading waves are propagated in a small sector in front of the crack while waves of unloading are propagated in all other directions.

Experimental Investigation of the Angled Elliptic Notch Problem in Tension

Polymethylmethacrylate (PMMA) plates with angled elliptic notch are experimentally investigated under monotonic tension. The major interests of this investigation are the direction of crack initiation on the boundary of the notch and the critical stress that causes the crack initiation. It is found that the “fracture angle” in this investigation is generally smaller than that obtained from PMMA plate with slit crack which was reported in the literature. Furthermore, the paths of crack propagation are experimentally determined and “lance-like” fracture surface is observed.

Growth of arterial cracks in polymethyl methacrylate plates containing "silver" cracks

1. We have studied the influence of previously formed surface SC of various orientations on the force and kinetic characteristics of a slowly growing arterial FC. The subject of investigation was industrial glass based on polymethyl methacrylate. Steady growth of the FC was achieved in our experiments by applying torque in order to split lamellar samples.

Fracture trajectories in a biaxially stressed plate

A specially designed rig has been used to examine the phenomena of crack growth in centrallynotched plates of polymethyl methacrylate under biaxial stress. Attention has been directed particularly towards investigating the phenomenon of path instability, viz. the deviation of a crack from its expected path with increasing transverse stress. Cracks grown under a biaxial stress system, whose transverse component, acting parallel to the crack, exceeds the normal component, do so in an S-shaped curve centred on the original, straight notch. Stress intensity factors for such a crack are estimated by superposition of related known solutions. On the assumption that crack extension takes place with opening displacements only at the tip, that is, the crack tip stress field remains symmetrical, the observed dependence of path geometry on the degree of stress biaxiality is explained.

Fracture under complex stress — The angled crack problem

Experiments are described in which thin plates of polymethylmethacrylate were fractured with cracks set at various angles to an applied uniaxial stress. While there is substantial agreement with previous analytical predictions, it is shown that inclusion of the stress component parallel to the crack can improve the correlation between linear theory and experiment, using a critical stress at a critical distance interpretation of the stress intensity factor criterion.

Propagation of steady shock waves in polymethyl methacrylate

The particle-velocity histories associated with the compression waves produced by the planar impact of polymethyl methacrylate plates were observed by means of laser interferometry. The impact velocity and the thickness of material through which the wave passed were varied from 0.06 to 0.64 mm μsec and from 6 to 37 mm respectively. Over this range of impact velocities, the observations disclosed a shock followed by a smooth transition to the maximum particle-velocity; the speed and magnitude of the shock varied non-linearly with the impact stress. For impact velocities below 0.3 mm μsec , the wave was steady. A steady-wave analysis based on finite linear viscoelasticity theory has been shown to be in good agreement with the experimental observations.

Use of polymethyl methacrylate plates for electron beam measurements at energies above 1 MeV

Flat plates of clear polymethyl methacrylate 1 8 in. thick exposed to an electron beam develop a characteristic coloration whose optical density can be measured with an ordinary photographic densitometer. Calibration of the optical density against electron exposure has been obtained together with information about fading exposure. The energy dependence of the calibration has also been measured. A few examples of the application of this technique to electron beam measurements are given.

輸血の血小板に及ぼす影響

1. In order to discide the method by which the platelet count in the circulating blood might be measured as accurately as possible, both Olef's and Fonio's methods were investigated. Glass and polymethyl methacrylate plates were used in both methods. Olef's method with glass plate was proved to be the best of the four methods, since it was accompanied by the least error, great convenience and comparatively good protective action on the platelets.2. The change of the platelets following the transfusion of 200cc of the compatible blood was investigated by measuring the platelet count prior to, and 30min., 1 hour, 2 hours and 24 hours after the transfusion in 30 patients. The red blood cell showed little change in number and the change of the white blood cell count was not consistent. The platelet count in the circulating blood, on the hand, revealed a marked change.A. Change of the platelet counta) Transfusion of ACD containing, preserved blood in 10 cases;The peak of the change came one hour following the transfusion, and ranged from 24 to 56 percent decrease in 8 cases, and from 20 to 57 percent increase in 2 cases.b) Transfusion of sodium citrate containing, fresh blood in 10 cases;Decreased in 8 cases and increased in 2 cases. The changes and their recovery in this group occurred earlier than in a).The rate of the change in this group was about the same as in a).c) Transfusion of heparin containing, fresh blood in 10 cases;Decreased in 6 cases and increased in 4 cases. The rate of change, especially the increase rate, was more marked than in a) and b).B. Incidence of complicationsThe most frequent of all complications associated with blood transfusion was urticaria.In sodium citrate group of twenty patients, there was mild urticaria in 4 cases and pruritus in 1 case, i. e. 25% out of 20 patients.There was thrombocytopenia in all patients with complications. No correlation between the severity of thrombocytopenia and the symptomatology of complications was detected.In the heparin containing fresh blood group of 10 patients, there were 4 cases of urticaria (severe in one and mild in three) and 1 pruritus out of 6 thrombocytopenic patients, and 2 (moderate in one associated with coughs and severe in another associated with fever) out of 2 thrombocytotic patients. The thrombocytosis of the last 2 patients was as marked as up to 75 and 73 percent in increase.3. In another group of 30 patients who were administered 20cc of intravenous MgSO4 solution 30min. prior to the transfusion of 200cc ACD preserved blood, the changes of the platelet count and complications following the transfusion were investigated. MgSO4 was administered in 10% in water in 10 cases and 10% in 5% glucose solution in 20 cases.The variation of the r. b. c. count was the same as the one encountered in 5 cases (17%) out of 30 patients in this group and, on the other hand, 15 cases (75%) out of a control or sodium citrate group of 20 patients. The difference above mentioned was statistically significant with less than 0.1% of significance level.As to the complications, there were two cases of urticax is (6.9%) in this group. The difference of the incidence of urticaria between this group and the control was again statistically significant with 7% of significance level.

Transformation of Adsorbed Water on Solid Surfaces and its Dielectric Losses and Conductivities

The adsorption isotherm of water vapor on nonalkali glass cloth was obtained at 25°C, and its dielectric power factor was measured also in the frequency range of 80 kc/sec∼11 mc/sec. The power factor of glass cloth and surface dc conductivities of nonalkali glass, soda glass, fused silica, Teflon, and polymethylmethacrylate plates increased rapidly to maximum peaks, when they were exposed to water vapor, and then gradually decreased to certain constant values. These phenomena may be interpreted as physical picture of phase changes in the adsorbed water phase from the amorphous state to the crystalline state, as well as the deposit films of evaporated metals on solid surfaces. But the surface conductivity of polycapramide increases as the moisture content increases with time, suggesting a rapid absorption of water molecules into the solid. An analysis of this process of phase change of adsorbed water is outlined.