Failure analysis of A286 carrier panel fasteners

The observation that carrier panel fasteners recovered from the Columbia appeared to have fractured with minimal macroscopic ductility led to concern that stress-corrosion cracking (SCC) or other age-related degradation processes in the A286 bolts may have been the cause of failure during re-entry. To assess this hypothesis, several recovered fasteners having a brittle fracture appearance and several fasteners that fractured in a more ductile mode were analyzed. The results provided the information necessary to discount the “stress-corrosion” hypothesis and conclude that the fasteners failed by some unidentified tensile load after being weakened by high-temperature grain growth and liquid aluminum attack. This article is based on a presentation given on October 19, 2004, at the session on “The Space Shuttle Columbia: A Forensic Materials Perspective” as part of the Failure Analysis and Prevention Symposium at ASM International’s Materials Solutions Conference and Exposition in Columbus, Ohio.     

Columbia tragedy: High-temperature materials chemistry and thermodynamic considerations of the breached wing leading edge

Metallurgical analysis of debris from the leading edge of the breached left wing of the Columbia space shuttle demonstrated that the temperatures inside the leading edge structural subsystem exceeded 1760 °C (3200 °F). A thin, relatively uniform deposit containing aluminum, Inconel, and Cerachrome was found inside most of the reinforced carbon-carbon composite panels. Such deposition indicates the melting and concurrent deposition of spar, attachment hardware, and insulation. In contrast, panel 8 showed thick, nonuniform deposits suggesting this panel was the breach location. The characteristics of these nonuniform deposits provided indications of plasma flow direction and plasma impingement locations and were helpful in establishing the sequence of failure events. In addition, no indications of A286 were found in the deposits inside panel 8. The lack of evidence for A286 suggests that the breach location was remote from the A286 fittings. This article is based on a presentation given on October 19, 2004, at the session on “The Space Shuttle Columbia: A Forensic Materials Perspective” as part of the Failure Analysis and Prevention Symposium at ASM International’s Materials Solutions Conference and Exposition in Columbus, Ohio.     

Residual analysis for ARCH(p)-time series

In this paper we provide consistency and distributional convergence results for functions of residuals from an ARCH(p)-time series. An application to a goodness-of-fit problem is also discussed.     

Influence of the curvature of thin-walled elements with cracks on the parameters of fracture (Theoretical and experimental investigation)

The influence of curvature of a cylindrical panel containing a crack on the value of the J-integral in the process of axial loading is investigated. We study the entire range of curvatures of the panel, namely, from a plate to a closed cylindrical shell. The critical values of the J-integral are determined numerically according to the experimentally obtained values of critical loads corresponding to the onset of crack propagation. The contributions of membrane and bending strains to the total value of the J-integral are evaluated. In the case of an almost plane panel, we analyze the influence of nonlinear bending (buckling) in the vicinity of the crack on the increase in the J-integral. The influence of crack length on the critical value of the J-integral is studied. __________ Translated from Problemy Prochnosti, No. 3, pp. 75–84, May–June, 2006.     

Preparation and properties of (CdS) x -(PbS)1 −x thin-film composites

A modified chemical deposition process is employed for the preparation of thin-film (CdS) _x -(PbS)_{1 −x} composites with 0·2 ≤x ≤ 0·8. Cadmium sulphate, lead acetate and thiourea are used as the basic source materials. The electrical conductivity is found to decrease with increasing composition parameterx up to 0·5 and increase for further increase inx. The composites are polycrystalline as is revealed from XRD and microscopic observations and show phases of both cubic and hexagonal CdS, cubic CdO and PbS, and tetragonal PbO and PbO₂. Additional peaks of free elemental Cd and S have also been observed. For all the phases no significant variation in lattice parameters withx has been observed. The optical absorption studies show the presence of four well-defined absorption edges at approximately 0·45 eV, 1·05eV, 1·80 eV and 2·35 eV, at the same energies for allx values. The absorption coefficient is of the order of 10⁴ cm⁻¹ and mode of band-to-band transition is of the direct type.     

Thermal analysis of used and radiation treated polycarbonate (L-MW) biomaterial

γ-radiation treatment of radiation sterilized polycarbonate biomaterials has been carried out to ensure efficient disposal by incineration. Low molecular weight polycarbonate sterilized with 2·5 Mrad dose ofγ-radiation was further treated with different doses ofγ-radiation. The radiation-treated samples were subjected to thermogravimetry. The sterilized sample and the 7·5 Mrad-treated sample showed similar properties. These samples do not leave any residue during thermal decomposition.     

Evidence for Dielectric (e–h) and Superconducting (e–e) Pairing in Cuprates

It is demonstrated that anomalous behavior of cuprates can be described in a natural way by the model with partial dielectrization of conduction electron energy spectra (EES). In such a model, near the Fermi surface (FS), there are formed the fours of charged particles (FCP) rather than independent electron–hole (e–h)- and electron–electron (e–e)-pairs. Since the bonding energies are the same for Cooper (e–e)- and dielectric (e–h)-pairs, then the temperature of SC transition T _c due to the Bose-condensation of FCP can be much more than the temperature of Bose-condensation of Cooper pairs only. The dielectric (e–h)-transition is connected with structural phase transformation in the cuprate system, formation of stripe structure, etc. The model successfully describes the presence of maximum at T _c (x)-curve, T-dependence of pseudogap (PG) and SC-gap, effect of nonmagnetic impurities to T _c , STM and ARPES spectra and other properties of cuprates.     

Computational investigation of GanAl (n = 1–15) clusters by the density-functional theory

Low-lying equilibrium geometric structures of aluminum-doped gallium cluster Ga_nAl (n = 1–15) clusters obtained by an all-electron linear combination of atomic orbital approach, within spin-polarized density functional theory, are reported. The binding energy, dissociation energy, and stability of these clusters are studied with the three-parameter hybrid generalized gradient approximation (GGA) due to Becke-Lee–Yang–Parr (B3LYP). Ionization potentials, electron affinities, hardness, and static polarizabilities are calculated for the ground-state structures within the same method. The growth pattern for Ga_nAl (n = 1–15) clusters is Al-substituted Ga_n + 1 clusters and it keeps the similar frameworks of the most stable Ga_n + 1 clusters except for Ga₈Al and Ga₁₃ Al clusters. The Al atom substituted the surface atom of the Ga_n + 1 clusters for n < 12. Starting from n = 12, the Al atom completely falls into the center of the Ga-frame. The Al atom substituted the center atom of the Ga_n + 1 clusters to form the Al-encapsulated Ga_n geometries for n > 12. The odd−even oscillations from Ga_nAl (n = 5) in the dissociation energy, the second-order energy differences, the HOMO–LUMO gaps, the ionization potential, the electron affinity, and the hardness are more pronounced. The stability analysis based on the energies clearly shows the clusters from n = 5 with an even number of valence electrons are more stable than clusters with odd number of valence electrons.     

Chemical and structural effects on the electronic states of (Hg, Tl, Pb, Bi)-based cuprate superconductors

The electronic energy bands have been calculated for the new single-layer and triple-layer Hg-based superconductors, HgBa₂CuO₄ and HgBa₂Ca₂Cu₃O_y, for the analogous Tl-and Bi-based materials, and for hypothetical Pb-based materials. As one moves across the last row of the periodic table, from Hg to Bi,s- andp-derived bands pass below the Fermi energy, to influence hole doping of the copper oxide planes and transport in the other layers of the material. The dispersion of these bands is significantly affected by the crystal structure. The calculations were performed with a simple chemical model.     

Measurements ofHc2(T) in Bi-Sr-Cu-O

H _c2(T) has been measured for thin BSCO films at temperatures down to 65 mK and pulsed fields up to 35 T.H _c2(T) diverged anomalously as the temperature decreased. At the lowest temperature, it was five times that expected for a conventional superconductor.     

Enhancement ofT c (∼ 103 K) in calcium-free Tl2Ba2CuO x (2201) compound

EnhancedT _c in calcium-free Tl compounds of the series Tl _m Ba₂Ca _n−1Cu _n O _x (2201) has been reported. Three different starting compositions (2201, 1201 and 2202) were studied extensively with varying conditions of preparation. Under optimized conditions (sintering temperature 970°C and duration 3–10 min) the highestT _c(onset) ranges from 103 K to ∼ 115 K andT _c (zero) ∼ 95 K was found. XRD studies showed the transformation of all the three nominal compositions into 2201 phase with differentT _cs.     

Magnetic properties of RRh3B2(R=La,Ce, Nd,Gd) compounds

The¹¹Bnmr results on RRh₃B₂(R=La, Ce, Nd and Gd) are reported. For CeRh₃B₂, specific heat and electrical resistivity are reported. From a comparative study of the¹¹Bnmr Knight shifts and the spin lattice relaxation times of these compounds it is shown that in CeRh₃B₂, there is strong hybridization of 4f states with the conduction electrons. A local moment on Ce with admixture of 4f and 5d–6s orbitals is suggested.     

Failure analysis of aluminum structural members on the space shuttle Columbia

Various aluminum parts, both castings and rolled sheet, were found among the Columbia debris. At first glance, these parts seemed to have failed in a brittlelike manner, contrary to normal aluminum fracture behavior. Light optical microscopy on the etched aluminum samples examined in this study revealed second-phase particles along the grain boundaries. It was also observed that at the elevated temperatures encountered during re-entry, some of the particles melted and wetted the grain boundaries. Large voids could be found between the grains near the crack tips. Energy-dispersive spectroscopy showed particles that were rich in iron. During re-entry of the shuttle, elevated temperatures caused melting of the second-phase particles, allowing them to wet the grain boundaries, a process called liquation. Cracks initiated and propagated through the grain boundaries, thus resulting in intergranular rupture that had the macroscopic characteristics of brittle failure of the aluminum.     

Evaluation of divergent N-echelon (s,nQ)-policies under compound renewal demand

In this paper, decentralized inventory control in a divergent multi-echelon network is considered. All stockpoints are controlled by continuous review (s,nQ)-installation stock policies. Due to the fact that orders from a stockpoint to its predecessors may have to wait, this delay must be incorporated into the lead time of an arbitrary replenishment. We develop analytical approximations for the first two moments of this waiting time. These results enable us to accurately approximate the relevant performance characteristics at each stockpoint, given its (s,nQ)-policy. The performance measure considered in this paper are fill rate and average physical inventory. The analysis can easily be extended for other performance measures. The main contribution of this paper is the fact that the results apply to arbitrary divergent multi-echelon systems, with stochastic transportation times, arbitrary lot sizes and compound renewal demand. Correspondence to: Gudrun P. Kiesmüller     

Fluctuation-induced excess conductivity in the compounds CaREBaCu3O7−y (RE=La and Sm)

The compounds CaREBaCu₃O_7−y (RE=La and Sm) are tetragonal at room temperature withT _c between 60 and 70 K. The single-phase compounds were prepared by solid-state reaction. The resistivity was measured by a four-probe technique in a continuous flow cryostat with the temperature being controlled to an accuracy of 10 mK. The resistivity vs temperature showed a break in slope around 180 K in CaLaBaCu₃O_7−y and around 220 K in CaSmBaCu₃O_7−y . The results were analysed for fluctuation conductivity from 180 K downwards. A plot of dρ/dT vsT showed a sharp peak atT _m =69·69 K for La compound and 66·00 K for the Sm compound. Detailed analysis of the resistivity in the regionT _on to 180 K was carried out using the procedure due to Veira and Vidal. The results are discussed in this paper.     

Hysteresis in theIc(H) characteristics of high-temperature superconducting ceramics and thin films

The experimental hysteretic behavior of the transport critical current observed in ceramic Y-Ba-Cu-O and (Bi-Pb)-Sr-Ca-Cu-O, as well as thin film Y-Ba-Cu-O, are presented. The data are analyzed semiqualitatively. The results show certain similarities among the ceramic samples and the films.     

Availability and reliability of k-out-of-(M+N):G warm standby systems

Redundancy or standby is a technique that has been widely applied to improving system reliability and availability in system design. In most cases, components in standby system are assumed to be statistically identical and independent. However, in many practical applications, not all components in standby can be treated as identical because they have different failure and repair rates. In this paper, one kind of such systems with two categories of components is studied, which is named k-out-of-(M+N):G warm standby system. In the system, one category of the components is of type 1 and the other type 2. There are M type 1 components and N type 2 components. Components of type 1 have a lower failure rate and are preferably repaired if there is one failed. There are r repair facilities available. By using Markov model, the system state transition process can be clearly illustrated, and furthermore, the solutions of system availability and reliability are obtained based on this. An example representing a power-generator and transmission system is given to illustrate the solutions of the system availability and reliability.     

epoline electronic Online Filing (eOLF)

An office-wide project set up in 1999, epoline^® has been designed to improve the efficiency of the EPO and the range of services it offers to its customers, the intellectual property community. This article, the second in a special series on epoline^®, presents the epoline^® electronic Online Filing service, enabling applicants and attorneys to submit patent applications and documents to the EPO electronically. The history of the system is outlined, as well as the way it works and its advantages. In conclusion, the scheduled enhancements to the system are described.     

Structural analysis of high-Tccuprate superconductors

We have shown in this paper that members of the Tl-Ba-Ca-Cu-O and Bi-Sr-Ca-Cu-O superconducting families fabricated so far are built up of superconductor-semiconductor arrays. Four general homologous series are written down for these two families. The basic fundamental block in each series is itself a superconductor. We suggest that the Y-Ba-Cu-O family has a similar characteristic if YBaCu₂O_5-d is a superconductor.