Effect Of Permanent Deformation Research Articles

Determination of creep compliance of asphalt mixtures at intermediate and high temperature using creep-recovery test

The linear viscoelastic (LVE) characterisation of asphalt mixtures in time domain is generally performed at temperature lower than 30°C to prevent the effect of permanent deformation. Although LVE properties in frequency and time domain can be mathematically interconverted, the determination of relaxation modulus and creep compliance through experiment is also necessary. This paper presents a method for determining the creep compliance of asphalt mixtures at intermediate and high temperature, at which permanent deformation takes place. Since the recovery of creep-recovery test is a pure LVE process, it was used to back-calculate the creep compliances (CCs) at various investigating temperatures. The results show that the CCs back-calculated from creep-recovery data achieve a good level of accuracy and repeatability. In addition, the obtained master curves of CCs agree well with those interconverted from dynamic modulus test data and the same shift factors are applicable for both creep compliance and dynamic modulus, phase angle.

Effects of Earthquake Faulting on Civil Engineering Structures

Ground motion characteristics, deformation and surface breaks of earthquakes depend upon the causative faults. Their effects on the seismic design of engineering structures are almost not considered in the present codes of design although there are attempts to include in some countries (i.e. USA, Japan, Taiwan, and Turkey). In this study, the authors first describe ground motions, crustal deformation and surface break observations caused by earthquakes having different faulting mechanism. Then some laboratory experiments were carried out to simulate the motions during normal and thrust faulting and their effects on model structures. And then, the effects of surface ruptures and deformations due to earthquake faulting on the response and stability engineering structures through observations in recent great earthquakes are presented. Finally, some recommendations for the design of structures with the consideration of permanent ground deformation in addition to ground shaking, which may be used in the development of seismic codes incorporating the effect of permanent deformation on structures, are proposed.

Permeability of Porous Friction Course Pavements

This study investigates the effect of permanent deformation on the permeability of different asphalt porous friction course (PFC) pavements with heavy vehicle simulator (HVS) testing. The testing was performed under controlled temperatures, speeds, and loads. HVS rutting tests were performed with single and dual wheels. Under dual-wheel loading, dust was added to one of the tire tracks to determine the impact of aerially deposited dust on surface clogging of permeable pavements. Permeability measurements were performed to evaluate clogging related to dust and permanent deformation. Measurements were made on each test section before and after HVS operation with both ASTM C1701 and the National Center for Asphalt Technology (NCAT) methods. Results obtained from this study showed that ( a) permeability measured by ASTM and NCAT methods were correlated, especially when a smaller ASTM ring was used, but generally the values measured by the ASTM method were larger than those by the NCAT method; ( b) sections with thinner PFC layers were more prone to clogging, with after-HVS permeabilities close to zero; ( c) the majority of reduction in permeability values (40% to 60%) occurred after about 2,000 repetitions (less than 6-mm downward rut depth) and in most cases the permeability was reduced to near zero after 5,000 to 30,000 repetitions; and ( d) the addition of dust particles (<38 μm) did not significantly change the permeability of PFC layers; this finding indicated that the loss of permeability was primarily because of permanent deformation accumulated during the HVS operation. For this reason, the rutting performance of PFC pavements should be considered to assess the long-term effectiveness of permeable pavements for stormwater runoff control and management.

FEM Analysis for Sealing Performance of Hydraulic Pressure Brake Hose Caulking Portion

Usually, development of automobile brake hose and power steering hose has been realized through evaluating several actual prototype hoses experimentally. Recently, high durability and high development effect for brake hose has been required because periodic exchange for the brake hose has not been requested any more. In this study, therefore, stress analysis by FEM is performed to the crimped portion of hydraulic pressure brake hose in order to promote the development of the automobile hoses more efficiently. It is found that large normal stresses σr in the radial direction appear at the crimped portion between the nipple and inner rubber. The results suggest that several grooves on the nipple surface may be useful because they cause large σr, which may improve the sealing performance. The effect of permanent deformation of the rubber on the sealing performance is discussed by assuming initial deformation of the rubber at the crimped portion.

Potential Drawbacks of Using Ethylene-Vinyl Acetate (EVA) in Fabricating Athletic Mouthguards

Although the most commonly used material in athletic mouthguards, ethylene-vinyl acetate (EVA) may not be the most ideal material for the absorption of shock forces. Non-laminate form EVA absorbs approximately 40-65% of the energy of impact leaving a significant amount of momentum transferred to the substrate (teeth). EVA is a thermoplastic material that can be softened by the application of heat and is subject to the development of a permanent deformation set upon continued impact. PURPOSE: This investigation tested the mechanical properties of a popular non-laminate EVA material used in fabricating athletic mouthguards to determine: 1.) the effect of permanent deformation on EVA's energy absorption capability, and 2.) the effect of temperature on energy absorption. METHODS: We measured the capacity of the material to dissipate energy upon impact using a Charpy tup impact head mounted on a Tinius Olsen Model 92T pendulum (ASTMD6110-02). The device was set to impart either 1.13 J or 3.0J of energy to the specimen. To determine permanent deformation set, the EVA material was impacted in the same location over a series of 25 drops. To determine the effect of temperature on EVA energy absorption, the specimen was cooled to −50°C and impacted every 5°C as it warmed to room temperature. The specimen was then heated to +50°C in a convection oven and impacted every 5°C as it cooled to room temperature. RESULTS: Energy absorbed, when impacted with 1.13J of energy, decreased 2.3% by the 4th impact and a total of 3.4% by the 25th impact. Energy absorbed, when impacted with 3.00J of energy, decreased 5.7% by the 2nd impact and a total of 7.0% by the 25th impact. When the specimen was impacted with 1.13J between ±50°C, energy absorption varied from a high of∼75% of the impact energy at −10°C to a low of ∼36% of the impact energy at −50°C. Energy absorption continued to decrease as its temperature continued to increase from approximate room temperature (∼22°C) until the EVA material started to become more viscous at ∼40°C. CONCLUSION: The mechanical performance characteristics of commercially available EVA-based mouthguard materials decreased in their ability to dissipate energy at the extremes of temperature and as frequency of focal impact increased thereby indicating a strong need for a new material platform resistant to these effects.

The resistivity of polycrystalline wires in relation to plastic deformation, and the mechanism of plastic flow

The subject of metallic conduction of electricity has long been a source of difficulties, which are far from having been overcome by the many admirable and ingenious theories recently put forward. The peculiarities of the different individual metals, as exemplified, for instance, in the variation of the Wiede-mann-Franz ratio from metal to metal seem to fall right outside any scheme so far elaborated. At present it is only possible to treat a metal as if it were a homogeneous crystal, the insufficiency of which assumption may be the source of many of those discrepancies between theory and experiment now attributed to fundamental properties of the electron in metal. Any experimental evidence concerning variations in electrical conductivity which can be produced in one pure metal by mechanical treatment should therefore be of some interest for the general problem. In particular the effect of permanent deformation upon electrical conductivity in metals is full of obscurity, and seems to offer a field for experiment. It was decided to investigate the variations of conductivity with certain simple types of deformation which attend the flow of soft metals. The flow of polycrystalline wires under constant stress has been investigated by one of us, and the changes of mechanical properties with time examined. The process of flow can be analysed into three phases:—an initial stretch which occurs within a very short time of the application of the stress; a continuous flow, the rate of which decreases with time, called, from the constant used to express it, the β-flow; and a flow at constant rate per unit length which occurs simultaneously with the β-flow and continues until the wire breaks. The formula expressing the flow is l = l 0 (1 + β t ⅓ ) e kt where l is the length at time t , and l 0 , β and k are constants. Since the formula was first put forward analogous formulæ, involving t ⅓ , have been found by other workers for different substances. Thus Filon and Jessop found for celluloid l = l 0 + at ⅓ + bt , and Peirce has expressed the decrease of the couple required to maintain constant torsion in a cotton fibre by a formula c = c 0 + ae - β t ⅓ , so that a term in t ⅓ apparently represents with some generality the observed behaviour of solids during flow. In former publications the general features of the behaviour were expressed in terms of crystal structure, but at the time no evidence from other sources could be adduced to support the hypothesis. The object of the present investigation is to measure the specific resistivity of the metal during the plastic extension, and to use the data so obtained to elucidate the changes of structure which take place in a polycrystalline wire when it is extended. One of the chief results has been to show that the β-flow has a real physical significance, and is due to the rotation of the axes of the crystallites which constitute the polycrystalline wire. Experiments have also been carried out on the resistivity of single crystal wires, the results of which will be published in the near future.