Initial Stage Of Penetration Research Articles

Non-local theory of high-rate straining followed by structure formations

A new hydrodynamic theory based on non-equilibrium statistical mechanics is developed to describe the structure formation in dynamically deformed materials. Self-consistent non-local formulation of the boundary-value problem for a high-strain-rate process is reduced to a nonlinear operator set similar to some resonance problems. The branching of solutions to the problem determines both scales and types of the formed internal structure. The theory is applied to the shock wave propagation in solids. The experimentally observable velocity decay proves to be closely connected with such kinetic characteristics as a velocity dispersion and dissipative structure formation. A penetration problem for a long flat rigid plate into a visco-elastic medium is considered accounting for the dynamic structure formation following the high-rate straining in the framework of the non-local self-consistent approach. The approximate solution has shown that the mesoscopic structures formed during the initial stage of penetration can effect on the steady-state stage.

Dynamic hardness of high-strength steel and titanium alloy

Essential results of experimental studies on dynamic hardness (an average pressure on the cone face of a rigid rod at its impact indentation into the surface layer of a thick plate) of a homogeneous rolled steel (HRA) and a titanium alloy are presented in this paper. Significant influence of the impact velocity on dynamic hardness of materials tested follows from the analysis of the experimental data. Specific energy of the formation of a conical cavity (per unit volume of displaced material) decreases with an increase in the indentation velocity and the conical cavity depth. At further process of indentation, corresponding to the initial stage of penetration (the cavity depth exceeds the length of the rod conical head) the average pressure increases with the impact velocity. Combined influence of viscosity effect and rise in temperature at plastic flow should be taken into account in order to explain the above relations.

Design issues in clinical studies of the in vivo volumetric wear rate of polyethylene bearing components.

The issue of wear of ultra-high molecular weight polyethylene bearing surfaces in total hip and knee replacements is, without doubt, one of the dominant themes in contemporary orthopaedics. Thus, an array of relevant facets of this topic have been extensively and intensively researched, spawning, in the process, a very large volume of literature. The main topics that have been studied are the place of wear in the hierarchy of degradation modes of polyethylene bearing surfaces, the role of polyethylene wear particles in the in vivo longevity of the prosthesis, the methods of determining the extent of wear of polyethylene bearing components (for example, the acetabular cup, acetabular cup liner, or tibial insert), the magnitude of the volumetric wear rate, the relationship between the results of in vitro wear-testing of polyethylene specimens or components and the clinical performance of polyethylene components, and the key factors influencing the clinical wear of polyethylene components. It is widely acknowledged that wear is one of many degradation modes that affect polyethylene bearing surfaces in vivo (other modes include creep, delamination, and burnishing) and that, under certain circumstances, it is not the predominant one. For example, polyethylene creep of the liner predominates during the initial stages of penetration of the femoral head into the acetabular cup, but additional penetration after the first twelve to eighteen months in situ is due to wear24. A consensus has emerged that wear of polyethylene bearing components is implicated in the aseptic loosening of hip and knee implants, and in the development of osteolysis around those implants, through resorption of the periprosthetic bone initiated by a foreign-body-giant-cell granulomatous tissue reaction. This biological reaction arises in response to the polyethylene and other wear particles (such as acrylic cement and metal) that are released into the periprosthetic bone. Furthermore, in the …

The infection of nymphal Baetisbicaudatus by the mermithid nematode Gasteromermis sp.

1. This study reports the infection in nymphs of a bivoltine mayfly host (Baetisbicaudatus) in a high‐elevation watershed by the mermithid nematode Gasteromermis sp. Infection by Gasteromermis causes mortality in two ways. Fifty per cent of the infections do not successfully develop beyond the initial stage of penetration and result in the early death of both host and parasite.2. Infected hosts that survive this initial stage are rendered completely sterile by the infection (reproductively dead). In addition to complete sterility, the emergence size of parasitized nymphs is reduced and development time lengthened compared with unparasitized nymphs.3. Parasite infection levels are stable from year to year at one site, but with a higher incidence of infection in the mayfly summer generation. Size differences between the generations at the time of infection may account for their different susceptibilities.4. Within a year infection levels vary seasonally and spatially from 1 to 71%. Seasonally, there is a condensation of parasitized hosts towards the end of development as unparasitized nymphs emerge earlier. Spatially, infection levels show a downstream decline that may result from upstream dispersal by infected hosts or differential parasite survivorship at different elevations.

High-resolution backscattered electron images in the scanning electron microscope

In this discussion the words “high resolution imaging” of a solid sample in the scanning electron microscope (SEM) mean that details can be resolved that are considerably smaller than the penetration depth of the incident electron beam (EB) into the specimen. “Atomic resolution” in either the transmission electron microscope (TEM) or scanning transmission electron microscope (STEM) means that columns of atoms are resolved.Image contrasts in the backscattered electron (BSE) image are strongly affected by the specimen tilt and by the position and energy sensitivity of the BSE detector. The expression “BSE image” generally implies that the specimen is normal to the beam and the detector is above it. This shows compositional variations in the specimen with a spatial resolution limited by the spreading of the EB during the initial stages of penetration. This is similar in basic principle to the Z-Contrast method in the STEM that shows atomic resolution from a thinned single crystal mounted in the magnetic field of the focusing lens.

Drop penetration into a thin porous medium

A thermodynamic analysis of the penetration of a drop into a thin porous medium is presented. It is shown that the thinness of the porous medium and the finite size of the drop play an important role in the phenomenology of penetration. In particular, a new equilibrium state is revealed in relationship with basal penetration, which is the situation where the liquid penetrates just beneath the base of the drop. The basal penetration equilibrium may be stable or metastable, depending on the parameters of the system. “Phase diagrams” are presented and show the regions of complete penetration, basal penetration, and no penetration as a function of the true contact angle and the thickness of the porous medium relative to the drop size. The existence of the basal penetration equilibrium is shown to be sensitive to the relative thickness of the medium. For very thin media, it may entirely replace the mode of complete penetration. In addition, a saddle point in the free energy surface of the system, which corresponds to the initial stage of penetration, is revealed. This observation implies that initially the driving force for penetration is low and the process is expected to be slow.

An electron-microscopical analysis of capture and initial stages of penetration of nematodes by Arthrobotrys oligospora.

A detailed analysis was made of the capture and subsequent penetration of nematodes by the nematophagous fungus Arthrobotrys oligospora using different electron-microscopical techniques. Capture of nematodes by this fungus occurred on complex hyphal structures (traps) and was effectuated by an adhesive coating, present on these trap cells. The adhesive layer was largely fibrillar in nature and was absent on cells of normal hyphae. Following capture, penetration hyphae were formed at those sites where the trap cell wall was anchored to the nematode cuticle by the adhesive. New walls of these hyphae were formed underneath the original trap cell walls, which were partly hydrolysed to allow growth and development of the penetration tubes through the adhesive coating towards the cuticle. Our observations indicated that the cuticle of the nematode was subsequently penetrated by the penetration tubes by mechanical means. After penetration a large infection bulb was formed from which trophic hyphae arose. Cytochemical experiments indicated that the sites of penetration of the cuticle were intensely stained for acid phosphatase activity. At later stages of infection activity of this enzyme was present throughout the nematode contents; the enzyme was most probably secreted by complex membranous structures associated with the cytoplasmic membrane of the infection bulb and the trophic hyphae.

The Porous Structure of Paper, an Approach from Mercury Porosimetry

In order to cultivate a better understanding on the porous structure of paper, the actual significance of mercury penetration curve obtained from mercury porosimetry has been studied on the basis of microscopically direct observation. The results for laboratory handsheets made of bleached kraft pulp are given.It is confirmed that the pressuring curves of mercury penetration on duplicate runs show sufficient reproducibility at all pressure range except at extremely low pressure range (less than 10 psi) which is influenced on overlapped spaces between the test pieces. At the initial stage of penetration the spaces between the test pieces and the relatively large voids on the surface are filled by mercury. Once mercury is forced into interconnected fiber to fiber channels, the penetration curve rises at the pressure which depend on the porous structure of handsheets. Since the penetration curve for unbeaten handsheets were equal to that for beaten handsheets above 200 psi range, it can be presumed that the penetration of mercury between fibers and into the lumens or pit chambers of individual fibers is complete at about 200 psi.The penetration curve concretely represents the effects of sheet formation on the porous properties of paper. For example, the neck of channels between fibers became narrower with increasing basis weight of the sheets. In addition to remarkably decrase in the volume of mercury penetrated, the rising point of penetration curve for beaten handsheets shifted to higher pressure in compared with that for undeaten one.The frequency distribution of spacings between adjacent fibers obtained from microscopic experiment of the thin cross-section of unbeaten handsheets can be fitted to a lognormal distribution. The median value of the distribution was 7.5 μ in the X-Y direction and 3.1 μ in the Z direction, whereas the pressure required to penetrate into the channels between fibers was the range of about 15 to 60 psi which equivalents to the range of radius about 7.1 to 1.8 μ of cylindrical capillaries.