Herbert F. Schiefer

Stress-Strain Relationships. in Yarns Subjected to Rapid Impact Loading

If a textile yarn, marked at intervals along its length, is struck transversely by a rifle bullet, a flash photograph taken shortly after impact will reveal a shifting of the marks caused by passage of a strain wave. Analysis of these shifts provides data on the dis tribution of strain and strain velocity in the wave. Tests were performed on specimens of a high-tenacity nylon and a high-tenacity polyester yarn, to determine strain-velocity distributions at various times after impact and at various impact velocities. The observed distributions were then compared with the predictions of a theory which assumed that stress-strain behavior was independent of strain rate. From discrepancies between theo retical and observed results, it was concluded that at strain levels up to 9%, significant creep and stress relaxation occurred within 30 μ sec after impact, but in the time interval 30 μ sec to 300 μ sec, creep and stress relaxation were negligible. For strains of the order of 1%, the 30 μ sec creep and stress ...

Stress-Strain Relationships in Yarns Subjected to Rapid Impact Loading Part IV: Transverse Impact Tests

If a textile yarn segment, clamped at each end, is impacted transversely at the mid point, the stress-strain curve for this yarn can be obtained from measurements on a high speed photographic record of the yarns motion. This paper describes the apparatus and procedure used. Stress-strain curves for high rates of straining, of the order 5000%/sec., obtained by this method are given for high tenacity nylon, Fortisan, and Fiberglas. Comparison with stress-strain data obtained at conventional rates shows that these mate rials have higher initial moduli, and that their stress-strain curves remain linear up to higher stress values, when the testing rate is high. The breaking tenacities are slightly greater and breaking elongation slightly smaller at these high test rates.

Stress-Strain Relationships in Yarns Subjected to Rapid Impact Loading Part I: Equipment, Testing Procedure, and Typical Results1,2

Equipment is described for elongating yarns by longitudinal impact at velocities rang ing from 10 to 100 m/sec. The rate of straining at impact varies from about 100,000 to 500,000% per min. A procedure is discussed for obtaining load-elongation curves for loading and for unloading of the specimen and for loading to rupture in a time interval of only a few milliseconds. The results of a typical loading and unloading test are presented.

Interpretation of Tests for Resistance to Abrasion of Textiles

The resistance to abrasion of sixteen cotton fabrics, which varied systematically in warp and filling yarn number and in ends and picks, was determined with the Schiefer abrasion testing machine, using No. 600A silicon carbide waterproof abrasive paper as the abradant and a total load of 2 lbs. on the specimen in one testing procedure, and a blade abradant and a total load of 20 lbs. on the specimen in a second testing procedure. The rate of abrasion in the first testing procedure was over ten times as great as that in the second. The results for the testing proce dures could be represented very well by the following equations: where R is the number of rotations of the abradant, W is the warp yarn number, F is the filling yarn number, E is the ends per inch, P is the picks per inch, and the other quantities are con stants. It was found that the rankings of the sixteen fabrics were different for the two testing procedures. This difference is due mainly to the fact that a given change in any one construc tion factor does not always result in quantitatively comparable changes in the resistance to abrasion obtained by the two procedures. This sort of difference is obtained, and should be expected, when comparing results of highly accelerated laboratory abrasion tests with results of comparatively slow rates of wear in service or performance tests. The resistance to abrasion of eight other fabrics of intermediate constructions obtained with each abradant agreed very well with the values computed by using the above two equations.

Textile Testing in Germany: Part II. Serviceability Evaluation of Textiles

aspects of the measurement of resistance to wear and the evaluation of serviceability have received considerable attention in recent years in the United States, England, and Germany. This work has resulted in the development of numerous wear-testing instruments. The research of the textile technologists of Germany on the evaluation of the relative serviceability of textile fibers was intensified during the war in an endeavor to obtain the optimum amount of

Solution of the Problem of Producing Uniform Abrasion and Its Application to the Testing of Textiles

A general mathematical solution to the problem of producing uniform abrasion over a plane area of a specimen from every azimuthal direction was worked out. This solution requires that the abradant and the specimen rotate in the same direction and with the same angular velocity. The specimen may revolve about the center of the abradant with any angular velocity in the same direction as or in the opposite direction from its direction of rotation. The specimen must not extend beyond the boundary of the abradant. Simple revolution of abradant about specimen and of specimen about abradant without rotation of either are special solutions. The special solution in which the specimen does not revolve about the center of the abradant is the simplest one from mechanical considerations. A machine based upon this special solution is described and pre liminary results obtained with it are discussed.

Improved Single-Unit Schiefer Abrasion Testing Machine

An improved single-unit Schiefer abrasion testing machine was developed. It can be adapted for testing a great variety of materials under a wide range of test conditions. Different types of specimen holders and abradants can be used with the machine. Both the pressure and the tension on the specimen can be fixed at selected values and maintained constant throughout the test period. A variety of materials, including woven, knitted, and coated fabrics, plastics, paper, leather, and other materials, were abraded with the machine. The abrasive wear of each material was found to be extremely uniform over the abraded area. The effect of the amount of plasticizer on the resistance to abrasion of plastics was readily measured. The rate of abra sion was directly proportional to the amount of plasticizer present. The abrasive wear in tests of woven fabrics appeared very similar to that which occurred in service. A quantitative method based upon the change in electrical capacitance of the specimen with abrasion was de scribed for evaluating the amount of abrasion. A quantity which is a measure of abrasive destruction or ruin was defined. This quantity was used to obtain an iso-ruin map of a large area of a trouser leg. This iso-ruin map showed very clearly a number of areas at which ex cessive wear in service had occurred. The change of the abradant during abrasion tests is discussed. Carborundum paper, a generally used abradant, decreased very greatly in abrasive power. The spring steel blade abradant remained essentially constant, although in testing one resin-finished fabric the surfaces of this abradant became coated with the resinous substance, which greatly increased its abrasive power.

Note on the Disintegration of Wool in Abrasion Tests

The coating which formed on the abradant when a specimen of wool fabric was abraded and caused the rate of abrasion to increase approximately ten times in three successive tests was examined critically. Microchemical analyses showed that it had the same composition as the unabraded fabric. Infrared absorption curves of the coating and of the powder of the unabraded fabric, ground in a vibratory ball mill, showed the same absorption characteristics. Electron micrographs of the coating showed that it contained extremely small particles, many of which were approximately spherical in shape and about 100 to 200 A. in size. Similar particles were observed in the abraded debris when the specimen was kept wet with water during the abrasion test, and also in the powder into which the unabraded fabric was ground in the vibratory ball mill. It was concluded that the coating which formed on the abradant consisted of extremely small particles of wool which appear to correspond in shape and size to the elemental structural units (keratin molecules) proposed in recent concepts of the structure of wool.

Influence of Fiber Structure of Rayon on Swelling and Radial Density

Elod and a staff of about 60 had carried out important research in the well-equipped laboratories at Mulhouse on the structure, dyeing, and chemistry of protein, cellulose, and nylon. A list of the papers published since 1941 is included as Part III of this report. A copy of an unpublished manuscript by E16d and Fr6hlich was obtained from Kurt Mierisch, Technical Editor of Melliand Textilberichte at Hei-

4—CHARACTERIZATION OF THE HIGH-SPEED IMPACT BEHAVIOUR OF TEXTILE YARNS

This paper discusses how the behaviour on impact of textile yarns may be characterized in terms of such parameters as tenacity-strain data, breaking energy density, limiting breaking velocity, and critical velocity. Methods are given for obtaining the parameters from tests involving speeds of impact of 50 m/sec or less. At greater speeds of impact, strain-wave phenomena become appreciable, but the behaviour of the yarn may be studied by transverse impact methods. The results of a wave theory for transverse impact are given. The theory is then applied in a method for measuring longitudinal strain-wave velocity, and in two methods for obtaining tenacity-strain curves from high-speed transverse impact tests.