Specimen Breaks Research Articles

Tailored adhesion at polymer/nonpolymer interfaces

AbstractIn this investigation, block copolymers of deuterated polystyrene (dPS) and poly (2‐vinylpyridine) (PVP) have been used to modify the adhesion at polystyrene/soda lime glass interfaces. The fracture energy, Gs of these interfaces was measured using an asymmetric double cantilever beam specimen. The failure mechanism was investigated using forward recoil spectrometry (FRES) and Rutherford backscattering spectrometry (RBS). The areal density, ∑ of the dPS‐PVP block copolymer at the two fracture surfaces, as well as the fraction of the dPS block on the PS side of the fractured sample are measured directly by FRES. The fraction of the PVP block on the glass side of the interface can be found by quaternizing the PVP with methyl iodide and then using RBS to measure the amount of iodine on each fracture surface. Short dPS blocks (NdPS < 175) do not entangle effectively with the PS homopolymer and only very small increases in Gc can be achieved as the dPS block pulls out of the interface. If the dPS block is long (NdPS ≫ 175) and if ∑ is large, crazes can develop in the PS ahead of the crack. The crazed interface fails at low ∑ by breaking the block copolymer close to the styrene/vinylpyridine link. At higher ∑, if the PVP block is relatively short (NPVP = 95), the crazed interface fails by the PVP block being pulled off the glass. If both the PVP and dPS blocks are long (≫ 175), the Gc increases rapidly with increases in ∑, but the interface becomes so strong that the glass on the thinner side of the test specimen breaks. The dPS block and the PVP block are found on opposite sides of the fracture surface with most of the PVP on the glass and most of the dPS on the PS side of the interfaces. Finally, if the glass surface is modified by coating it with a self‐assembled hydrophobic monolayer produced from chlorodimethyloctadecylsilane (CDMOS), the interface becomes very weak and fails by pull‐off of the PVP from the CDMOS‐coated glass. Using these results it is possible to tailor the interfacial adhesion to produce a desired Gc within a wide range of possible values. © 1994 John Wiley & Sons, Inc.

Brittle fracture of solids caused by intense electron beams

In the mid 1960s, powerful pulse electron beam accelerators having a voltage of some millions of volts were invented and later used to fracture various materials. Experimental data analysis allowed discovery of a new mode of fracture in several ductile crystals caused by a specific energy supply to the crack tip. The mode differs from well known thermomechanical modes of fracture caused by the “ heat-thermostress-crack ” mechanism. This new mode is called the electron fracture mode (EFM). It is characterized by the following three special features, (i) Initial macrocracks in a specimen do not affect the threshold of fracture; that is, the value of the beam intensity at which the specimen breaks, (ii) The fracture of different materials, which can be very ductile at usual mechanical loads, occurs in a brittle manner; that is, the specimen usually splits by a crack without any residual deformation, (iii) The splitting cracks propagate with supersonic velocities. These data are controversial from the point of view of common fracture mechanics and, hence, they cannot be understood or explained from the traditional position. The purpose of the present study is to create a simple practical model of the EFM. The basic viewpoint can be briefly summarized as follows: during irradiation of a solid by a high intensity electron beam, some solid plasma clots are formed and act as “ blades ” or “ wedges,” cutting the crystalline specimen. In the Introduction, experimental data on the EFM are analyzed and discussed, while the peculiarities of the EFM are specified. As a result, it is concluded that the processes caused by the EFM are unusual for the common concepts of fracture mechanics. In Section 2 the invariant Γ-integrals of an electromagnetic deformable medium are modified for supersonic singularities. The basic model and some problems serving to explain and describe the EFM are formulated. In Section 3, the relativistic electron interactions in beams are considered. Using Γ-integrals, we derive the law of the interaction of two moving relativistic charges; that is, the generalized Coulomb's law for relativistic charges. In particular, when two relativistic electrons, e, move with the same velocity, v, one behind the other along a rectilinear trajectory, the force, F, acting upon the rear electron is equal to: ▪ where R is the distance between the electrons, c is the speed of light in the vacuum, and a is the phase-speed of light in a medium having electromagnetic constants, μ, ϵ, and ϵ'. It appears that two electrons moving faster than the phase-speed of light attract one to the other, as distinct from the common Coulomb law. Hence, the beams of such relativistic electrons tend to self-pack and self-compress. The latter problem is studied using a periodic chain model of the electron beam. In Section 4, the dynamic elastic problem of supersonic cutting by a thin wedge is formulated and solved, and the drag force is calculated. In Section 5, the problem of deceleration of the moving wedge is solved in quasi-steady approximation. The length of a resulting cut, that is, the final crack, is determined. Some applications of the analytical solutions are given. In Section 6, the theoretical results are analyzed and compared with experimental results. The role of relativistic electrons is estimated and some parameters of solid-state electron plasma clots are defined. In the Conclusion, the necessity of further study of this mysterious phenomenon is emphasized.

Why Direct Tension Test Specimens Break Flexing to the Side

Contrary to the traditional view, unnotched direct tension test specimens of quasi‐brittle materials that exhibit post‐peak strain softening do not deform symmetrically. After passing the peak load, the equilibrium path bifurcates and the secondary postbifurcation branch represents flexing to the side. The bifurcation is shown to be analogous to Shanley's bifurcation in elastoplastic columns. According to the thermodynamic criterion of stable path, the flexing to one side must occur even if the geometry is perfect and if the straightening effect of the moment of the axial force about the centroid of the deflected cross section is taken into account. The lateral flexing favors failure of the specimen at midlength. The phenomenon (which is similar to the recently discovered behavior of notched tensile fracture specimens) is first illustrated using a simple model in which the specimen consists of two rigid bars of unequal lengths, joined by a strain‐softening link. It is shown that flexing to the side is ret...

The experimental research onb value of AE for the rock specimens with pre-existing crack or notch under uniaxial compression

A lot of researches onb value have been made in seismology. Since the 1960’s Mogi, Scholz and others have studied AE of rock specimens in laboratory and discovered that it is related to natural earthquakes. All former researchers used integral specimens to studyb value in the laboratory. However a major earthquake is usually related to a existing seismic-fault in that area. For this reason, a series of fracture experiments with rock and glass specimens having pre-existing crack or notch is performed in order to examine the effect of preexisting crack tob value. The experimental results show that theb value begins to decrease as soon as the initiation of the crack and finally drop to a very low value when the specimen breaks unstably. Based on these, a brief discussion on the possible mechanism ofb value change for natural earthquakes is given.

A Technical Examination of the Chinese Buddhist Bronzes in the Freer Gallery of Art, Part B: Stable Lead Isotope Analysis

ABSTRACTStable lead isotope ratios were determined on sixty-four samples taken from sixty of the Buddhist bronze images which were examined and chemically analyzed by Jett and Douglas [preceding paper]. The data were grouped using multivariate techniques and were compared with an accumulated data base of lead isotope measurements on more than 700 ancient Chinese artifacts and more than 200 Chinese and Korean ores. One group of ten images which were all datable to a period of less than one century, Eastern Wei through Sui dynasties, form a nearly unique isotopic group which coincides only with an unusual group of Lengshuichong bronze drums. A second large group of thirty-two isotopically matching images contains almost all, fifteen out of sixteen, of the images attributed to the Northern Wei dynasty. The remaining members of this group are of later date, extending into the Tang dynasty, or are animal figures attributed more generally to the Six Dynasties. This group partially overlaps somewhat the isotope fields of some Western and Eastern Han mirrors and some of the Sackler ritual bronze vessels of the Shang and Zhou dynasties, but appears to have been derived from a different ore source from them. The remaining specimens break up into some very tentatively defined small groups of two to four specimens each and a small residue of four unique, unmatched specimens.

The influence of carbon and oxygen in the grain boundary on the brittle-ductile transition temperature of tungsten Bi-crystals

This paper describes the determination of the brittle-ductile transition temperature (BDTT) range of oriented bi-crystals with varying concentrations of carbon and oxygen as measured by Auger Electron Spectroscopy AES. Oriented symmetrical tilt bi-crystals were produced by welding together two single crystals along a common axis. Specimens of 1.6mm thickness were sectioned from the 8mm diameter bi-crystal by spark erosion. Because of the small specimen thickness, a simple three point bend test was used to determine the BDTT region. The load was applied parallel to the grain boundary plane and the BDTT determined as the range of intermediate temperatures between that for which the specimen bends without breaking (ductile domain) and that for which the specimen breaks without plastic deformation (brittle domain).

Study on Bending Fatigue Strength of Bevel Gears : 2nd Report, Bending Fatigue Strength of Straight Bevel Gears of Gleason Type

The bending fatigue strength and the bending fatigue breakage of straight bevel gears of Gleason type were investigated by carrying out bending fatigue tests (Wohler method) using a bevel gear pulsator of hydraulic type. The bending fatigue limit loads were also determined using the progressive load increase methods proposed by Prot, Henry and others, which consist in testing a few specimens raising the stress in equal increment until finally the specimen breaks, and they were compared with those obtained by Wohler method. Furthermore the existing equations of the bending strength for straight bevel gears were compared on the basis of the experimental results.

42—THE RAPID MEASUREMENT OF THE TENSILE PROPERTIES OF FIBRE BUNDLES PART II: EXAMPLES OF EXPERIMENTAL RESULTS

An account is given of the use of the bundle tester described in Part I of this series to determine the breaking force, work of rupture, and elongation at break of various textile specimens. Typical results (which include tests on wool staples and semi-processed materials) are reported.

A sphere compression test for measuring the mechanical properties of dental composite materials.

Traditional methods of determining the mechanical strength properties of composite restorative materials have for various reasons been found to be unsatisfactory. A new method of testing is described which follows more closely the situation in the tooth cavity and also is more suitable for glass-reinforced materials because they are subject to ‘brittle’ fracture. The theoretical aspects and examination of the way the spherical specimens break, together with the empirical relationships, have been analysed. Finally, results of tests performed on commercially available restorative materials are presented.

Investigation of Drawing and Heat-treatment in Swelling Solution for Poly (methaphenyleneisoPhthalamide) Film

The drawing and heat-treatment in dimethylformamide or dimethylacetamide aqueous solution were performed for poly (metaphenyleneisophthalamide) films, and the most suitable conditions on the concentration, temperature of swelling solution and the time of treatment were decided. Under the suitable condition, the films were drawn to 6 or 7-fold of the initial length. The initial modulus and tensile stress at break of the high-drawn specimens increased to as much as 5 or 6-fold of those of un-drawn one, and the change of elongation at break with draw ratio showed a maximum value. When the drawn specimens were heat-treated, the initial moduli increased much more.Above method for the drawing and heat-treatment can be made more easily than Du Pont's method, in which high-pressure steam is used. Also, changes in fine structure of the films by drawing or heat-treatment were investigated by optical and X-ray methods. From the results, it was clarified that the degree of orientation by optical method increased rapidly at the early stage of drawing, and changed gradually after the draw ratio 3. When the drawn specimens were heat-treated, the degree of crystallinity and orientation increased remarkably.

Research and Testing

Equipment, Programmes, Techniques and Projects. STRESS CORROSION TESTING MACHINE Saml. Denison & Son Ltd., Moor Road, Leeds 10, are now manufacturing a new environmental testing system — the T66 stress corrosion machine based on an original design licensed from British Aircraft Corporation (Operating) Ltd. of London. This machine is a four channel, vertical machine capable of testing 12 specimens simultaneously under load up to 10 tons (20,000 lb.). The specimens may be round or flat, three per channel, all loaded through special stainless steel holders and shackles. These shackles take over the specimen load when a specimen breaks, so maintaining load on the other specimens in the channel. Load is applied hydraulically and indicated on two facia dials. The hydraulic pressure is derived from an air/hydropump actuated by pressurised nitrogen. During a test the load on the specimens remains constant to plus or minus 100 lb. The environmental chamber consists of a polythene sleeve held in position by rubber O‐rings clamping on to Perspex top and bottom flanges thus making an airtight enclosure; into this can be fed the corrosive atmosphere. A salt‐spray unit is fitted in the centre for supplying one or all chambers. When sulphur dioxide is used, the supply from a cylinder is mixed with clean air and fed in via a flowmeter at 0.01–3 per cent mix.

A Rugged Semiautomatic Extensometer for Rubber

Abstract The evaluation of an elastomer—new or established—inevitably involves a study of tensile properties. ASTM procedure D 412 is generally used as a guide for the tensile testing of vulcanized rubber. In this method, an operator observes bench marks on the sample and records the modulus at every 100% elongation, the ultimate elongation, and the tensile strength at break. An extensometer has been developed to eliminate operator coordination and judgment factors from rubber tensile testing. It is simple and sufficiently rugged for routine testing. Its features are a counterbalanced guide rod with a sliding electrical contactor, and specimen followers which automatically unlatch to avoid being damaged when specimens break. In addition there is a counter for direct digital indication of elongation, and an electrical circuit which controls a short duration spark to mark the autographic chart. Experience in testing up to 5000 specimens per year has shown that the apparatus makes an inexperienced operator as effective as trained operators working under optimum conditions. The instrument has been used successfully on materials ranging from soft rubber to plasticized and filled poly (vinyl chloride).

On the change of the structure of cold worked titanium plate by welding

A titanium plate of 6mm thickness was ammealed for 30 minutes at 800°C and cold-rolled by maximum 63.6% and then edge-prepared. This plate was then welded by invert gas are tungusten (Argon gas T. G.), and was investigated on the phenomena occurred by welding heat, at the part of welding joints as well as in the base metal.The results of the exqeriment are summed up as follows:(1) When the cold-rolled titanium plate is welded, the structure of the deqosited metal, zone of grain growth, recrystallized zone, zone of recovery, and the base metal as rolled can be seen from the side of deqosited metal.(2) Banded and dendritic structure made by rapid cooling at the temperature of β→α transformation, 883°C, are seen in the zone of grain growth and deposited metal.(3) From the distribution of hardness at the welding joint, it is found that the deqosited metal and zone of grain growth are little harder than the recrystallized zone, and that the deviation of hardness is very remarkable, showing the unstability of the structure.(4) Results of tensile tests with specimens which is taken by cutting out verticully against the welding bead show that the tensile strength as welded state is about 42-43kg/mm2. The specimens are broken down at the recrystallized zone. This means that the tensile strength has nothing to do with the degree of working which is given to the base metal before welded.The tensile strength of the welding joint after annealing at 600°C for one hour is about 38-40kg/mm2 and specimens break down in the zone of grain growth or deposited metal.(5) The average size of recrystallized grains in the zone recrystallized by the welding heat depends upon the working degree which is given to the base metal before welded, and coarser grains are seen in the case of about five percent of cold working being given.

Stress-Strain Relationships in Yarns Subjected to Rapid Impact Loading

Samples of high-tenacity deacetylated cellulose acetate yarn were braided or plied and twisted by various amounts. Stress-strain data were obtained on these yarns at conventional rates of straining and under conditions involving transverse and longi tudinal impact at velocities near 40 m/sec. Strain-wave velocities were also measured. The effects of twisting and braiding were the same at high rates of straining and at conventional rates of straining. The addition of twist or braid caused the following effects. The initial slope of the stress-strain curve and the strain-wave velocity de creased. The bend in the curve at the yield stress became less sharp so that the stress- strain curve became more linear. The breaking tenacity decreased and the breaking elongation increased. The work required to break a unit mass of yarn material re mained unchanged. The calculated value of the longitudinal critical velocity at which a specimen breaks immediately upon impact in tension remained unchanged. Calculated transverse critical velocities tended to decrease as the yarn was twisted or braided.

Volume Changes and Dewetting in Glass Bead-Polyvinyl Chloride Elastomeric Composites under Large Deformations

Abstract Elastomeric materials loaded with inert filler have Theological properties which, on the one hand, are qualitatively like those of unfilled polymeric materials, but which, on the other hand, are unique to filled systems. Their stress-strain curves usually have several distinct regions which are similar to those for certain unfilled polymeric materials. The curves have an initial region in which the stress increases with strain, and here the modulus depends primarily on the amount of filler and the properties of the binder. In the second region, the stress may be roughly independent of the strain or may increase at a rate markedly less than that in the initial region. The transition between these two regions may be either gradual and hardly perceptible or sharp, with a well-defined yield point. Thus, in these two regions, the stress-strain curves may be like those for typical unfilled rubbers or for plastics, or they may resemble the curves for rubbers at low temperatures, which cold draw or neck. In the third region the stress increases more rapidly with strain than in the second region and continues to increase until the specimen breaks; again, this is similar to what is observed for certain plastics and rubbers. Thus, both filled and unfilled systems can have sigmoidal stress-strain curves which may or may not have distinct yield points. However, filled systems, and especially those in which the binder wets, but does not react chemically with the filler, exhibit the sigmoidal-type stress-strain curve for different reasons than do rubbers and plastics. In filled systems, the binder adheres to the filler initially, which reinforces or strengthens the system. However, in the transition and second regions of the stress-strain curve, adhesive bonds between the filler and binder break, a process called dewetting, and vacuoles form around the filler particles. After the adhesive bonds are essentially all broken, a further increase in strain only stretches the binder further and enlarges the vacuoles.

Magnetization Reversal in Uniaxial Films near to the Preferred Direction

It is now well known that uniaxial thin magnetic films can be made which have almost ideal square hysteresis loops in the preferred direction and almost straight line hysteresis loops in the hard direction. For this type of film, which can be prepared by evaporation from ingots of approximately 81:19 NiFe alloy, it is found that the switching time constant of the reversal process which occurs when magnetic fields are applied exactly in the easy direction can be very large. The switching process occurring when fields are applied at angle 10° to the preferred direction has been studied in detail, both by a new pulse response technique and by observation of the domain structure revealed by use of the Kerr magneto-optic effect. In the latter experiment, short pulses have been applied to the specimen and photographs taken of the domain pattern after each pulse. It was found that the specimen breaks into small domains whose area increases after each pulse and that eventually the filmcould be completely reversed if the pulse amplitude was between certain critical values. Curves were plotted of the pulse amplitude against the proportion of the film switched found by measuring the reversed area in the photographs. It was shown that the process is very well approximated by an equation of the form Sw = τ(H − H0),which implies a viscous damped process, and there is a critical nucleation field, which is less than the field required to move the walls. In the pulse response experiments, the switching time has been derived from the response to a reset pulse which was applied after a variable number of set pulses of variable amplitude. It was found that in some films there can be a rapid switching process, which is complete after about 100 mμsec, followed by a slow process lasting up to 10 μsec under the same conditions. From the experiments performed, it has been possible to compute a switching time constant which can be very large in some films. This constant is found to be correlated with the ratio p = Hc/Hk, where Hc is the coercivity in the easy direction and Hk is the rotational coercivity. If the film obeyed the simple coherent rotational model the pratio would be 1, and films which have p = 0.9 have been found have Sw = 0.3×10−6 oe μsec, whereas for p = 0.3, Sw = 7×10−6 oe μsec.

半月形みぞを有する炭素鋼の回転曲げ疲労について

The shafts with a wood-ruff key way, which revolve under the rotating bending load, have a weak point concerning the fatigue strength, because of the depth of the key way. We carried out experiments with regards to fatigue, using the specimens of carbon steel (S45C), on which a key way of every different width and depth is worked. The results obtained through our experiments are as follows:(1) When the key way width is only about one sixth of the shaft diameter, notch effects induced at the corners of key way give a greater influence on the fatigue strength, than the maximum bending stress at the middle of both sides of it, especially when the depth of key way is big. Most shafts of this sort are broken at the corner of key way.(2) When the way width is one-third or more of shaft diameter, the bending stresses induced at the middle of both sides of key way increase in accordance with the depth of it, therefore, the fatigue strength of shaft falls naturally. On the other hand, as notch effects at the corners of key way dicrease, the rate of lowering of the fatigue limit becomes gradually smaller. In this case, most specimens are broken at the middle of both sides of key way.(3) It was found from the experimental results that in the key way of the same dimension, overload breaks specimens at the middle of both sides of key way, while the load near the fatigue limit breaks them at the end of those due to notch effect.(4) When specimens break at the end of key way, most specimens have the origin of breakdown at both corners, where concentrated stress induced by notch effect is at its maximum.(5) According to the results of our experiments, we propose to set bounds to the dimension, making the way width within the range from 1/5 to 1/3 of shaft diameter, and the way depth below 2/5 of shaft diameter.

Research and Test Apparatus

Milliard Ltd. have produced a machine for ‘fatiguing’ a metal test specimen by means of sound waves instead of the more conventional mechanical strains. Ultrasonic power is generated electronically and applied to a magneto‐striction transducer. The vibrations produced are increased in amplitude by a step‐up velocity transformer and applied to the specimen, a short rod of the metal under test. The specimen is designed to be resonant at the applied frequency, so that standing waves are produced. At the point of minimum movement the strain is at a maximum, and eventually the specimen breaks there. The strains can be as much as 30 tons/sq. in. and can be applied at a rate of up to 20,000 times per second.

切欠を有する軟鋼の強さについて

We made the tension tests about the specimens of annealed mild steel with various circumferential notches, and made σ-q diagrams about each specimen, where σ indicates the tensile stress and q indicates the area contraction corresponding to every stage of loads during the tension tests. And so we required the relation between the sharpness of the notch and tensile strength σB, breaking stress on final area σT or area contraction ψ.Summary of the results is as follows:(1) Tensile strength σB increases when the notch becomes sharper, and approaches to cirtain maximum value.(2) Area contraction ψ decreases when the notch becomes sharper, and approaches to cirtain minimum value.(3) The ture breaking stress on final area σT increases at first but thereafter it decreases when the notch becomes sharper. For this reason we explained using the stress distribution in the section of the necked portion when the specimen breaks.