Rupture of Rubber. VI. Further Experiments of the Tear Criterion

1961 ◽  
Vol 34 (1) ◽  
pp. 66-75
Author(s):  
A. G. Thomas
Keyword(s):  
Natural Rubber ◽  
Test Piece ◽  
Fundamental Property ◽  
Elastic Strain Energy ◽  
Test Pieces ◽  
Tearing Energy ◽  
Different Shapes ◽  
Materials Used ◽  
T Values ◽  
Energy Balance Approach

Abstract In previous papers (I to V of this series), a tear criterion for rubbers has been proposed based on an energy balance approach. This equates the energy required to form new surfaces (the tearing energy) with the loss of elastic strain energy in the test piece. The tearing energy T is assumed to be characteristic of the material and so independent of the overall shape of the test piece. It is thus the fundamental property controlling tear behavior. The correctness of this approach was investigated by making tear measurements on test pieces of different shapes but of the same material and examining the constancy of the T values obtained. The results were consistent with the theory but not wholly conclusive, due primarily to the particular tearing behavior of the materials used (natural rubber gum vulcanizates). Another limitation was that accurate T values could be obtained only if they could be calculated directly from the measured tearing forces or elongations, and the required relationships were known for only two types of test piece. Clearly, the more test pieces available for comparison and the more they differ from each other in shape, the more stringent the test of the basic theory. In the present paper a third test piece is described, the necessary theory given, and experimental results presented on the three test pieces. By comparing the results from these test pieces, which are of widely different shapes, a critical test of the theory is possible. The choice of the experimental material is influenced by several factors. Previous measurements have been made on natural rubber gum compounds, which have the advantage of possessing excellent elastic properties but whose rupture characteristics are such that tearing occurs at a critical load. In contrast, a gum GR-S tears more or less steadily at a rate depending on the load, a characteristic which is experimentally advantageous for the particular test pieces described here. It was therefore used in this investigation.

Rupture of Rubber. V. Cut Growth in Natural Rubber Vulcanizates

1959 ◽  
Vol 32 (2) ◽  
pp. 477-489 ◽  
Author(s):  
A. G. Thomas
Keyword(s):  
Natural Rubber ◽  
Test Piece ◽  
Direct Method ◽  
Simple Extension ◽  
Test Pieces ◽  
Steady Rate ◽  
Unstrained State ◽  
Length Width ◽  
Applied Forces ◽  
Definition Of

Abstract It has been noted in Part I of this series (referred to hereafter as I), that if a nicked specimen of a natural rubber vulcanizate is slowly stretched, tearing occurs at the tip for quite small applied forces. In the initial stages, this tearing continues only as long as the deformation of the specimen is being increased, and virtually ceases if the deformation is held constant. This tearing is essentially time independent, and is termed “static” cut growth. If, however, the deformation is continued until the cut has grown by a few hundredths of a millimeter the growth becomes time dependent and catastrophic tearing takes place, the cut suddenly increasing in length by perhaps a millimeter or so. If a nicked specimen is alternately stretched and relaxed to the unstrained state, the cut gradually grows even though the applied force is less than that required to produce catastrophic tearing. This phenomenon is termed “dynamic” cut growth. This behavior can be compared to that of gum GR-S vulcanizates described in Part III, where static cut growth of the above type does not occur, a dead load on a test piece producing a more or less steady rate of cut growth. In the present paper, measurements on natural rubber gum vulcanizates only are described, and the numerical results expressed in terms of the theory developed in previous papers (Parts I, II and III). It has been shown in I and II that the tear behavior of differently shaped test pieces cut from thin sheets of thickness t may be correlated by means of the concept of the energy for tearing. This is defined as the value of T[=(1/t)(∂W/∂c)l] at the instant of tear, and is denoted by Tc. In the definition of T, is the total elastic energy stored in the test piece, c the length of the cut, and the subscript l indicates that the differentiation is to be carried out at constant displacement of those parts of the boundary that are not force-free. It was also shown that a convenient and direct method of obtaining Tc is by the use of the “simple extension” tear test piece described in I and shown in Figure 1, and this has been used for most of the experiments. Under most conditions, T for this test piece is nearly independent of the cut length, width of the test piece, and modulus of the rubber; T is very nearly equal to 2F/twhere F is the force applied to the arms. In the cases where the use of the above approximate relation between T and F introduces an appreciable error, the exact theory given in I was used.

Measurement of Tensile Strength of Natural Rubber Vulcanizates at Elevated Temperature

1982 ◽  
Vol 55 (1) ◽  
pp. 66-75 ◽  
Author(s):  
C. L. M. Bell ◽  
D. Stinson ◽  
A. G. Thomas
Keyword(s):  
Tensile Strength ◽  
Elevated Temperature ◽  
Critical Temperature ◽  
Natural Rubber ◽  
Test Piece ◽  
Flaw Size ◽  
High Tensile Strength ◽  
Test Pieces ◽  
Naturally Occurring ◽  
Natural Rubber Vulcanizates

Abstract The tensile strength of test pieces made from natural rubber vulcanizates drops abruptly at a critical temperature which can vary from 40 to 130°C. This variation in critical temperature is shown here to be a result of the variation in critical cut length with temperature. When the naturally occurring flaws in the test piece are smaller than the critical cut length, high tensile strength values occur, but when the flaws are longer than the critical cut length, low tensile strength values occur. The critical cut length decreases as the temperature increases, and the abrupt drop in tensile strength occurs as the critical cut length reaches the natural flaw size in the test piece. The natural flaw size in tensile test pieces depends on the sharpness of the cutter, and for tensile strength measurements at elevated temperature, it is shown that even a slightly blunt cutter may give markedly different results from a sharp one.

Role of Ozone in Dynamic Cut Growth of Rubber

1966 ◽  
Vol 39 (4) ◽  
pp. 1053-1064
Author(s):  
G. J. Lake ◽  
P. B. Lindley
Keyword(s):  
Natural Rubber ◽  
Test Piece ◽  
Critical Value ◽  
Rate Of Growth ◽  
Tearing Energy

Abstract The effect of ozone on the growth of cuts in rubber strips subjected to repeated tensile deformations has been investigated. At tearing energies below a critical value ozone accounts for all the cut growth, and in this region the rate of growth is substantially independent of tearing energy. At higher tearing energies, cut growth also occurs due to mechanico-oxidative rupture, the rate of this type of growth increasing rapidly with increasing tearing energy so that the effects of ozone are normally slight. For vulcanizates of natural rubber and SBR unprotected by anti-ozonant, the characteristics of dynamic ozone cut growth can be deduced from static measurements. If a natural rubber test piece is not allowed to relax to zero strain on each cycle, the effects of ozone are important over a wider range of tearing energy.

An Interchangeable Turning Sprue Bushing in a Multi Cavity Family Injection Mold

2012 ◽  
Vol 548 ◽  
pp. 600-604
Author(s):  
Rozana Mohd Dahan ◽  
Saiful Bahri Mohd Yasin ◽  
Zakaria Razak ◽  
Mohd Helmi Omar
Keyword(s):  
Temperature Distribution ◽  
Test Piece ◽  
Volume Shrinkage ◽  
Injection Mold ◽  
Melt Flow ◽  
Flexural Test ◽  
Test Pieces ◽  
The Family ◽  
Separate Injection

Interchangeable Turning Sprue Bushing (ITSB) is a small insert at the centre of core side used to change runner directions for injecting 2 different products in a separate injection mold by shifting the melt filling to the cavities. The development of ITSB is significant in cutting down cost and time consumed during fabrication of a multi cavity family mold. In this study, the tensile and flexural test pieces were designed using CAD Solidwork. The test pieces analysis was performed using CAE Cadmould simulation in order to observe the melt flow of four multi cavities family mold incorporated without and with ITSB insert. The Cadmould simulation was used specifically to analyse the melt filling, temperature distribution and volume shrinkage of the test pieces. The simulation result demonstrated that ITSB is a useful insert that can be used to overcome problems encountered in the family mold system by balancing the melt filling, minimize temperature distribution and reduced the differential of volume shrinkage of the test piece manufactured. ITSB also reduced the frequent defects formed during production such as short molding, flashing and warpage.

A novel method for evaluating the validity of dynamic accuracy test pieces for five-axis machine tools

2020 ◽  
Vol 234 (11) ◽  
pp. 2189-2210 ◽  
Author(s):  
Weiwei He ◽  
Liping Wang ◽  
Liwen Guan
Keyword(s):  
Test Piece ◽  
Machine Tools ◽  
Dynamic Error ◽  
System Model ◽  
Feed System ◽  
Mathematical Relationship ◽  
Dynamic Accuracy ◽  
Accuracy Test ◽  
Test Pieces ◽  
Five Axis

The detection method for direct machining the standard test pieces, which is commonly employed to exhibit the machining precision of five-axis machine tools, can truly reflect the dynamic accuracy of five-axis machine tools in the actual machining process. Existing theories on explaining the phenomenon that the ability of S-shaped test pieces to detect dynamic accuracy for five-axis machine tools are stronger than those of NAS979 test pieces mostly used the qualitative research methods, and they cannot be quantitatively used to reveal the mathematical relationship between machine tools and test pieces. Therefore, this article makes the first attempt to investigate the quantitative evaluation method for the validity of dynamic accuracy test pieces. The dynamic error function of the servo feed system in the frequency domain was derived first by establishing the mechanical system model and control system model. The method of dipole cancellation was used to acquire a simplified transfer function for the dynamic error affected by the input. Based on the zero-order hold property of the discrete input signals, the expression of dynamic error affected by input in the time domain, which intuitively shows the mathematical relationship among the machine tool performances, the test piece characteristics and the dynamic error of the servo feed system, was obtained. Then, the novel evaluation methods of the linear combinatorial value and the combinatorial linear combinatorial value were proposed. A series of comparative analyses between an S-shaped test piece and an NAS979 test piece were carried out based on the proposed new evaluation methods. A machining experiment conducted on a five-axis machine tool is used to verify the evaluation results.

COMPARISON OF SINE VERSUS PULSE WAVEFORM EFFECTS ON FATIGUE CRACK GROWTH BEHAVIOR OF NR, SBR, AND BR COMPOUNDS

2010 ◽  
Vol 83 (4) ◽  
pp. 391-403 ◽  
Author(s):  
G. Andreini ◽  
P. Straffi ◽  
S. Cotugno ◽  
G. Gallone ◽  
G. Polacco
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Natural Rubber ◽  
Crack Growth ◽  
Fine Tuning ◽  
Styrene Butadiene Rubber ◽  
Butadiene Rubber ◽  
Pulse Waveform ◽  
Tearing Energy ◽  
Styrene Butadiene

Abstract Fatigue crack growth experiments on carbon black-filled rubber compounds have been carried out to evaluate the influence of testing conditions over different compound formulations. Investigations on the influence of waveform, data acquisition, and compound formulation have been performed on strip-tensile specimens reproducing the mode I of crack opening. The response of three different compound formulations (based on either natural rubber, butadiene rubber, or styrene-butadiene rubber) to the application of two different waveforms, pulse and sine, has been analyzed, showing significant differences in fatigue behavior and ranking of the various compounds. Compared to the sinusoidal waveform, the use of a pulse waveform provided an improved correlation of the tearing energy with the crack propagation speed. This difference was particularly evident in the case of natural rubber and butadiene rubber, while it resulted negligible in the case of styrene-butadiene rubber. Such a different behavior could be attributed to differences in macromolecular chains orientation. Fine-tuning of video acquisition parameters provided an accurate observation of the crack growth process, as confirmed by the low standard deviation of the estimated tearing energy and crack growth rate.

The Attack of Ozone on Stretched Rubber Vulcanizates. II. Conditions for Cut Growth

1960 ◽  
Vol 33 (4) ◽  
pp. 1156-1165
Author(s):  
M. Braden ◽  
A. N. Gent
Keyword(s):  
Experimental Study ◽  
Tensile Stress ◽  
Natural Rubber ◽  
Critical Value ◽  
Rubber Sheet ◽  
Test Pieces ◽  
Rubber Vulcanizate ◽  
Present Part ◽  
Applied Tensile Stress ◽  
Made In

Abstract In Part I an experimental study was reported of the factors determining the rate of propagation of a cut through a stretched rubber sheet under the action of an atmosphere containing ozone. It was remarked that no growth took place from a small razor cut made in one edge of the test pieces unless a critical value of the applied tensile stress was exceeded. The value was quite small, of the order of 100 g/cm2 for a soft natural rubber vulcanizate. In the present part an examination is reported of the conditions necessary for a crack to form or, being present, to grow.

Effect of Crosslink Density on Cut Growth in Black-Filled Natural Rubber Vulcanizates

2002 ◽  
Vol 75 (5) ◽  
pp. 935-942 ◽  
Author(s):  
G. R. Hamed ◽  
N. Rattanasom
Keyword(s):  
Carbon Black ◽  
Natural Rubber ◽  
Crack Growth ◽  
Crosslink Density ◽  
Longitudinal Crack ◽  
Test Pieces ◽  
Filled Rubber ◽  
Longitudinal Cracks ◽  
Natural Rubber Vulcanizates ◽  
High Crosslink Density

Abstract Tensile strengths, σb, of gum and N115-filled natural rubber test pieces, with and without edge pre-cuts, have been determined. At low crosslink density, the regular (uncut) σb of filled and gum vulcanizates is similar. However, at high crosslink density, the gum NR becomes brittle, while the corresponding filled rubber remains strong and resistant to cut growth. It is proposed that the tightly linked gum does not strain-crystallize appreciably during stretching, but that its filled counterpart does. Carbon black appears capable of inducing crystallization in a network that alone remains amorphous during extension. Filled vulcanizates of various crosslink densities have similar normal tensile strengths ( ≈ 30 MPa), but strengths differ, sometimes more than twofold, if a pre-cut is present. Lightly crosslinked specimens containing a small cut have strengths that depend very weakly on cut size, c. Furthermore, these develop long longitudinal cracks from which catastrophic rupture initiates. With larger cuts, strength decreases more rapidly with increasing c, there is less longitudinal crack growth, and rupture initiates near the original cut tip. In contrast, the strength of a highly crosslinked vulcanizate is sensitive to small cuts and test pieces exhibit minimal longitudinal cracking before failure.

Crystallization in Natural Rubber. III. Filled Compounds

1955 ◽  
Vol 28 (2) ◽  
pp. 460-469
Author(s):  
A. N. Gent
Keyword(s):  
Natural Rubber ◽  
Rubber Matrix ◽  
Simple Extension ◽  
Test Pieces

Abstract Measurements are described of the changes of volume accompanying crystallization in filled vulcanized natural rubber, and of the corresponding relaxation of stress in extended test-pieces. The observed changes in the rate of crystallization and relaxation of stress are attributed to the reduction in mobility of the rubber molecules in the neighborhood of foreign particles and to the effective higher orientation of some elements of the rubber matrix when the filled vulcanizate is subjected to simple extension.

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