Undamaged Systems Research Articles

The effect of cumulative damage on the ballistic performance of plain weaves

This paper investigates the effect of cumulative damage on the energy absorption capability of plain-woven fabric systems. The cumulative damage was generated by creating pre-damaged holes, aiming to simulate the post-impacted sample targets. Ballistic impact tests were performed to characterize the ballistic protection of the pre-damaged and undamaged systems, and FE simulation was used to study the underlying mechanisms of energy dissipation. The results showed that the pre-damaged systems appear to be less protective than the undamaged system in most cases. The ballistic performance of the fabrics is more sensitive to the pre-damaged holes that are located on the primary yarns than that on the secondary yarns. When the primary yarns are broken, the holes are detrimental to the evolution of the transverse deflection but are beneficial in increasing the amount of energy dissipated by frictional sliding during the yarn pull-out process. Angle-plying the constituent layers of multi-ply panels is found to be useful in minimizing property degradation. It was also determined that the angle-plied systems absorb less energy than the aligned system regardless of the existence of the pre-damaged holes.

Analysis of automotive gearbox faults using vibration signal

Abstract The objective of this work is to identify the presence of damages and to diagnose the damaged component in automotive gearboxes by comparing the vibration signals of the damaged and undamaged systems. The vibration signals were obtained in the gearboxes test bench taking into account ten samples approved by subjective method (based on human hearing) and three gearboxes damaged (two with bearing damaged and one with gear tooth damaged). The signals were obtained through five accelerometers positioned in the samples and each test comprises ten different steps with different coupling configurations of the gears. Different signal analysis techniques based on wavelet transform, mathematic morphology and energy (entropy) were used to verify the presence of damage in the systems. The presence of damage to the systems is verified directly by comparing the energy levels and entropy of the signals of the damaged and undamaged systems for the ten steps tests. A signal processing technique combining pattern spectrum and selective filtering in certain frequencies ranges was used for identification of component failures. This technique will, further on, be part of a diagnostic and quality control system that will be able to evaluate and identify the damaged component at the automotive gearbox.

Structural Health Monitoring Using Piezoelectric Sensors and Actuators

Structural health monitoring (SHM) is an inevitable component of modern civil and aerospace structures. It essentially detects the damages in the system by evaluating the performance parameters by the integration of sensing and possibly also actuation devices into the structure. In this paper damage detection process in an aluminium cantilever plate using piezoelectric sensors and actuators is simulated. Possible root damage such as transverse crack and longitudinal crack are studied. The results are compared with undamaged case. The plate is actuated using PZT actuators and performance is evaluated using PVDF sensors. Modelling for PZT/PVDF and structural parts are carried out using coupled field finite element PLANE223 ofAnsys(TM) finite element package. Strain response at the root of the cantilever plate is captured as the voltage output of the PVDF sensor. Strain response is directly related to the voltage generated in the PVDF sensor. The percentage variation of the fundamental frequency is found to be less than 3% in the present study and hence it is not taken as an index of damage. The transient voltage response captured with the transient coupled field analysis shows variation up to 24% as a signature between damaged and undamaged systems. Therefore, the present study suggests transient response evaluation using PVDF sensor is a suitable evaluation technique for the cases under consideration.

Info-gap robustness of an input signal optimization algorithm for damage detection

Info-Gap Decision Theory is adopted to assess the robustness of a technique aimed at identifying the optimal excitation signal to be used for active sensing approaches to damage detection. Here the term “active sensing” refers to procedures where a known input is applied to the structure to enhance the damage detection process. Given limited system response measurements and ever-present physical limits on the level of excitation, the ultimate goal of the mentioned technique is to improve the detectability of damage by increasing the difference between measured outputs of the undamaged and damaged systems. In particular, a two degree-of-freedom mass–spring–damper system characterized by the presence of a nonlinear stiffness is considered. Uncertainty is introduced to the system in the form of deviations of its parameters (mass, stiffness, damping ratio) from their nominal values. Variations in the performance of the mentioned technique are then evaluated both in terms of changes in the estimated difference between the responses of the damaged and undamaged systems and in terms of deviations of the identified optimal input signal from its nominal estimation. Finally, plots of the performances of the analyzed algorithm for different levels of uncertainty are obtained, enabling a clear evaluation of the risks connected with designing excitation signals for damage detection, when the parameters that dictate system behavior (e.g. stiffness, mass) are poorly characterized or improperly modeled.

Modelling of dissolved H in Ga stabilised δ-Pu

The behaviour of hydrogen in Ga stabilised δ-Pu has been investigated using atomistic computer simulation techniques. We have considered only the solid solution of H in Pu–Ga. H diffusivity in the undamaged material was calculated and was shown to depend on the Ga concentration of the Pu–Ga alloy. Furthermore, localised regions of high Ga concentration within the material were shown to block H diffusion pathways. These are important findings and could allow for the possibility to control H diffusion if it were possible to control the Ga configuration within the system. The interaction of H with simple point defects was also investigated and suggests that H will behave differently in cascade damaged systems compared to undamaged systems. Vacancies were observed to trap any H interstitials that enter their vicinity, while the likelihood of dissociation was very low, effectively reducing the H diffusion coefficient to zero. On the other hand, binding energy calculations show that it is energetically unfavourable for a H interstitial to be close to a Pu interstitial. No long range interaction between H and the single point defects was observed.

Nerve growth factor induces P2X(3) expression in sensory neurons.

Glial cell line-derived neurotrophic factor (GDNF) and nerve growth factor (NGF) are neuroprotective for subpopulations of sensory neurons and thus are candidates for pain treatment. However, delivering these factors to damaged neurons will invariably result in undamaged systems also being treated, with possible consequences for sensory processing. In sensory neurons the purinergic receptor P2X(3) is found predominantly in GDNF-sensitive nociceptors. ATP signalling via the P2X(3) receptor may contribute to pathological pain, suggesting an important role for this receptor in regulating nociceptive function. We therefore investigated the effects of intrathecal GDNF or NGF on P2X(3) expression in adult rat spinal cord and dorsal root ganglia (DRG). In control spinal cords, P2X(3) expression was restricted to a narrow band of primary afferent terminals within inner lamina II (II(i)). Glial cell line-derived neurotrophic factor treatment increased P2X(3) immunoreactivity within lamina II(i) but not elsewhere in the cord. Nerve growth factor treatment, however, induced novel P2X(3) expression, with intense immunoreactivity in axons projecting to lamina I and outer lamina II and to the ventro-medial afferent bundle beneath the central canal. In the normal DRG, we found a greater proportion of P2X(3)-positive neurons at cervical levels, many of which were large-diameter and calcitonin gene-related peptide-positive. In both cervical and lumbar DRG, the number of P2X(3)-positive cells increased following GDNF or NGF treatment. De novo expression of P2X(3) in NGF-sensitive nociceptors may contribute to chronic inflammatory pain.

Replacement of synaptic terminals in lamina II and Clarke's nucleus after unilateral lumbosacral dorsal rhizotomy in adult cats

Evidence from previous light-microscopic studies suggested that lumbosacral dorsal rhizotomy in cats elicits sprouting of converging undamaged systems into partially deafferented Clarke's nucleus and lamina II. We therefore applied quantitative electron-microscopic methods to determine whether this sprouting is associated with replacement of synaptic terminals (reactive reinnervation). We used stereological and morphometric methods to estimate terminal number per cross section in right and left lamina II and Clarke's nucleus in adult cats after acute and chronic unilateral (right-sided) lumbosacral deafferentation. Planimetric measurements of area indicated no significant shrinkage of either region as a result of the deafferentation; an increase in area occupied by glial cytoplasm (gliosis) equaled the decrease occupied by axonal components. The gliosis appears to persist indefinitely, although the degenerative debris stainable with conventional light-microscopic methods does not persist. Analysis of the synaptic population of lamina II reveals that the large central or "scalloped" terminals comprise a substantial fraction (greater than 40%) of the total area occupied by terminals in control material and that this population is largely lost upon deafferentation, leaving a large population of small terminals with spherical vesicles. Nevertheless, estimates of total terminal number indicate no difference between control and deafferented lamina II, suggesting a rapid and virtually complete replacement of lost dorsal root terminals by small terminals containing spherical vesicles. Terminal number in Clarke's nucleus also remains constant despite the loss of the dorsal root input. We conclude that there is also a virtually complete and rapid replacement of lost terminals in Clarke's nucleus by terminals containing spherical vesicles. These data provide an example of a case in which axonal sprouting demonstrated with light-microscopic methods is associated with electron-microscopic evidence of reactive reinnervation.

STUDIES ON THE FUSARIA WHICH CAUSE WILT IN MELONS: II. THE EFFECT OF LIGHT, NUTRITION, AND VARIOUS CHEMICALS ON THE SPORULATION OF CERTAIN FUSARIAL ISOLATES, AND PRELIMINARY INVESTIGATIONS ON THE ETIOLOGY OF WILTING OF THE MUSKMELON FUSARIUM

Light was shown to affect the amount of macrospore production in a number of Fusarium species. Macrospore production and the ratio of macrospores to microspores increased with increasing light intensity and vice versa. Only colony areas exposed to light during active growth produced macrospores on potato dextrose or Czapek's agars. Light also greatly stimulated macrospore production on V-8 vegetable juice agar. Both carbon and nitrogen sources were also important in determining the kind and amount of sporulation in the species tested. Colony growth was appressed in light, and pigmentation of the mycelium often was produced in response to light.Various chemicals, known to be enzyme inhibitors, induced different effects on growth and sporulation, depending on the substrate used as the carbon source. For example, sodium fluoride inhibited growth and sporulation when glucose was the substrate, but was without effect when sodium acetate, which supports equally vigorous growth, was the substrate.Studies on the etiology of wilting indicated that the muskmelon Fusarium produces at least three chemical fractions which may contribute to wilting. One was thermostable, non-dialyzable, apparently a protein, and possibly an enzyme. The second was thermostable and was probably a low molecular weight carbohydrate. These two induced wilting in plant cuttings rather than in intact plants, whereas the third fraction induced wilting in plants with undamaged root systems, and was thermostable, partially dialyzable, and stable through a wide pH range. Appropriate tests, however, indicated also that translocation through the vessels was significantly interfered with in plants showing incipient or more advanced wilting symptoms.