Volume 7, Issue 5, 01 May 1936
Index of content:
7(1936); http://dx.doi.org/10.1063/1.1745382View Description Hide Description
Measurements of the penetration tensions in paper of a series of creosotes distilled from a single coal tar are reported (the penetration tension being the product of the surface tension and the cosine of the contact angle). It is found that these data conform to two equations: one, previously developed by others from theoretical considerations of the effects of variation in size and distribution of capillary pores upon the theoretical equation of flow, the other, an empirical relationship which is less difficult to apply in more practical problems where many data must be analyzed. The creosote‐paper contact angles are shown to be zero or extremely small. Possible errors in the paper strip method are discussed and the importance of calibrating each strip with a reference liquid is demonstrated. The failure of Washburn's equation, which has received considerable attention in the field of fibrous penetration, is shown to be due to the neglect of the hydrostatic head term. The penetration tensions of these creosotes are unaltered by the presence of adsorbed water.
- RHEOLOGY SECTION
7(1936); http://dx.doi.org/10.1063/1.1745383View Description Hide Description
Data are given showing that it is possible for rubber to soften in one direction and stiffen in another direction simultaneously during a test in the St. Joe Flexometer. Both effects are mainly the result of heat, the softening being due to plastic flow, while the stiffening is due to the substantial elimination of plastic flow because of the rapidity of flexure. Static and dynamic tests on heated test pieces, and stress‐strain data on various sections of test specimens at several stages of breakdown indicate that failure in dynamic tests is due partially to mechanical fatigue, but mainly to heat effects. Results on anisotropic pigments such as asbestine, clay, magnesiumcarbonate, and acicular and non‐acicular zinc oxides show that the heat generation, breakdown time, flexing load, and vertical deflection are functions of the shape and orientation of the pigment particles. Variations in breakdown time from 16 to 160 minutes have been obtained by changing the orientation of pigment particles. Data on ``grain'' effect in high gum stocks are also given.
7(1936); http://dx.doi.org/10.1063/1.1745384View Description Hide Description
The stresses around large obstacles in strained rubber were studied with the assumption that the effects would be similar with actual pigment particles. The effects of variations in the size and shape of the obstacles on the stress concentration were investigated and an explanation offered for the stiffiening of rubber by pigments based on the change in slope of the rubberstress strain curve. The various average diameters of a series of zinc oxide samples were measured and their relationship with some physical properties of rubber compounds determined.
7(1936); http://dx.doi.org/10.1063/1.1745385View Description Hide Description
A solution of the three‐dimensional elasticity equations for a homogeneous isotropic solid is given for the case of a concentrated force acting in the interior of a semi‐infinite solid. This represents the fundamental solution having a singular point in a solid bounded by a plane. From it may be derived, by a known method of synthesis, the solutions for the semi‐infinite solid which correspond to the solutions known as nuclei of strain in the solid of indefinite extent.