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InGaAs and Ge avalanche photodiodes are compared for the effects of 63-MeV protons on dark current. Differences in displacement damage factors are discussed as they relate to structural differences between devices.
Total ionizing dose, displacement damage dose, and single event effects testing were performed to characterize and determine the suitability of candidate electronics for NASA space utilization. Devices tested include optoelectronics, digital, analog, and bipolar devices.
Total ionizing dose, displacement damage dose, and single event effects testing were performed to characterize and determine the suitability of candidate electronics for NASA space utilization. Devices tested include optoelectronics, digital, analog, and bipolar devices.
Total ionizing dose, displacement damage dose, and single event effects testing were performed to characterize and determine the suitability of candidate electronics for NASA space utilization. Devices tested include FPGAs, optoelectronics, digital, analog, and bipolar devices.
We present results and analysis investigating the effects of radiation on a variety of candidate spacecraft electronics to heavy ion and proton induced single-event effects (SEE), proton-induced displacement damage dose (DDD), and total ionizing dose (TID).
We present results and analysis investigating the effects of radiation on a variety of candidate spacecraft electronics to heavy ion and proton induced single-event effects (SEE), proton-induced displacement damage dose (DDD), and total ionizing dose (TID).
Graphite has been a core structural material and neutron moderator since the first man-made chain reaction experiment in Chicago. This article will discuss the requirements of what makes graphite a good solid moderator. The manufacture and properties of some currently available near-isotropic and isotropic grades are described. The major features of a graphite moderated reactors are briefly outlined. Displacement damage and the induced structural and dimensional changes in graphite are described. Recent characterization work on nano-carbons and oriented pyrolytic graphites that have shed new light on graphite defect structures are reviewed, and the effect of irradiation temperature on the defect structures is highlighted. Changes in the physical properties of nuclear graphite caused by neutron irradiation are reported. Finally, the importance of irradiation induced creep is presented, along with current models and their deficiencies.
Conformal coatings provide environmental protection for sensitive military electronics. Preliminary MCNP™ modeling of metal oxide impregnated acrylic conformal coatings indicates an effective shield for gammas below 10 keV and a reduction in neutron displacement damage to Si-based electronics across the Watt spectrum. This work provides data which can allow an optimal overall shielding worth per total weight to eventually be evaluated.
A method for performing progressive damage modeling in composite materials and structures based on continuum level interfacial displacement discontinuities is presented. The proposed method enables the exponential evolution of the interfacial compliance, resulting in unloading of the tractions at the interface after delamination or failure occurs. In this paper, the proposed continuum displacement discontinuity model has been used to simulate failure within both isotropic and orthotropic materials efficiently and to explore the possibility of predicting the crack path, therein. Simulation results obtained from Mode-I and Mode-II fracture compare the proposed approach with the cohesive element approach and Virtual Crack Closure Techniques (VCCT) available within the ABAQUS (ABAQUS, Inc.) finite element software. Furthermore, an eccentrically loaded 3-point bend test has been simulated with the displacement discontinuity model, and the resulting crack path prediction has been compared with a prediction based on the extended finite element model (XFEM) approach.
The composite solid/analog device affine equations are shown to be elastically and electrically material independent. Analog experimental solutions yield the stress and displacement fields of the composite solid for a wide range of physical variables.
The Lip-field approach was introduced in Moës and Chevaugeon (2021) as a new way to regularize softening material models. It was tested in 1D quasistatic in Moës and Chevaugeon (2021) and 2D quasistatic in Chevaugeon and Moës (2021): this paper extends it to 1D dynamics, on the challenging problem of dynamic fragmentation. The Lip-field approach formulates the mechanical problem to be solved as an optimization problem, where the incremental potential to be minimized is the non-regularized one. Spurious localization is prevented by imposing a Lipschitz constraint on the damage field. Here, the displacement and damage field at each time step are obtained by a staggered algorithm, that is the displacement field is computed for a fixed damage field, then the damage field is computed for a fixed displacement field. Indeed, these two problems are convex, which is not the case of the global problem where the displacement and damage fields are sought at the same time. The incremental potential is obtained by equivalence with a cohesive zone model, which makes material parameters calibration simple. A non-regularized local damage equivalent to a cohesive zone model is also proposed. It is used as a reference for the Lip-field approach, without the need to implement displacement jumps. These approaches are applied to the brittle fragmentation of a 1D bar with randomly perturbed material properties to accelerate spatial convergence. Both explicit and implicit dynamic implementations are compared. Favorable comparison to several analytical, numerical and experimental references serves to validate the modeling approach.
Winding fill, coil fill, or packing factor, is critical to the performance of many types of electromagnetic devices from electric machines to actuators, transformers, inductors, etc. One technique to increase the packing of conductors in the winding area is to compress round magnet wire conductors in a die, so that they deform and air voids between coil turns are removed. The winding layout of the coil turns on a bobbin before compression has a direct impact on the achievable coil fill and the damage to the coil insulation or conductors after compression. It is thought that winding the turns in an orthocyclic pattern on the bobbin before compression would minimize damage to the turns. This however causes turns to displace during the winding compression process. A new pre-compression winding pattern is proposed, a spaced orthocyclic winding, to minimize turn displacement and damage. A design of experiments study has been carried out to optimize this winding method and to compare it to the traditional orthocyclic winding.
Radiation effects in minerals and ceramics are quite distinct from effects observed in metals. This is largely due to interactions between radiation and the electronic structure of insulating materials that are unique compared to metallic conductors. Most notably, insulators exhibit property changes when energetic particles lose energy to electrons in the solid, whereas metals are unaffected by electronic energy losses. In addition, displacive radiation damage effects (atoms being knocked off their lattice sites by energetic particles) are much more complex in insulators, due to the complexities of their crystal structures (multiple cation and anion sublattices). In this presentation, we will focus on the atomistic mechanisms responsible for radiation damage in minerals and ceramics, when energetic particles lose energy while penetrating a solid. We will consider several examples, including (i) irradiation induced color center formation in gemstones; (ii) latent defects in alkali halides (relevance to thermoluminescent detectors); (iii) radioactive decay-induced amorphization of natural minerals; and (iv) extended defect formation and phase stability in complex oxides.
This paper documents recent TID (including ELDRS) and proton damage test results obtained by JPL. Unusual test results, such as abnormally low or high failure levels or unusual failure or response mechanisms, are emphasized.
The objective of this cooperative agreement was to seek computationally efficient ways to optimize aerospace structures subject to damage tolerance criteria. Optimization was to involve sizing as well as topology optimization. The work was done in collaboration with Steve Scotti, Chauncey Wu and Joanne Walsh at the NASA Langley Research Center. Computation of constraint sensitivity is normally the most time-consuming step of an optimization procedure. The cooperative work first focused on this issue and implemented the adjoint method of sensitivity computation in an optimization code (runstream) written in Engineering Analysis Language (EAL). The method was implemented both for bar and plate elements including buckling sensitivity for the latter. Lumping of constraints was investigated as a means to reduce the computational cost. Adjoint sensitivity computation was developed and implemented for lumped stress and buckling constraints. Cost of the direct method and the adjoint method was compared for various structures with and without lumping. The results were reported in two papers. It is desirable to optimize topology of an aerospace structure subject to a large number of damage scenarios so that a damage tolerant structure is obtained. Including damage scenarios in the design procedure is critical in order to avoid large mass penalties at later stages. A common method for topology optimization is that of compliance minimization which has not been used for damage tolerant design. In the present work, topology optimization is treated as a conventional problem aiming to minimize the weight subject to stress constraints. Multiple damage configurations (scenarios) are considered. Each configuration has its own structural stiffness matrix and, normally, requires factoring of the matrix and solution of the system of equations. Damage that is expected to be tolerated is local and represents a small change in the stiffness matrix compared to the baseline (undamaged) structure. The exact solution to a slightly modified set of equations can be obtained from the baseline solution economically without actually solving the modified system. Sherrnan-Morrison-Woodbury (SMW) formulas are matrix update formulas that allow this. SMW formulas were therefore used here to compute adjoint displacements for sensitivity computation and structural displacements in damaged configurations.
The objective of this cooperative agreement was to seek computationally efficient ways to optimize aerospace structures subject to damage tolerance criteria. Optimization was to involve sizing as well as topology optimization. The work was done in collaboration with Steve Scotti, Chauncey Wu and Joanne Walsh at the NASA Langley Research Center. Computation of constraint sensitivity is normally the most time-consuming step of an optimization procedure. The cooperative work first focused on this issue and implemented the adjoint method of sensitivity computation (Haftka and Gurdal, 1992) in an optimization code (runstream) written in Engineering Analysis Language (EAL). The method was implemented both for bar and plate elements including buckling sensitivity for the latter. Lumping of constraints was investigated as a means to reduce the computational cost. Adjoint sensitivity computation was developed and implemented for lumped stress and buckling constraints. Cost of the direct method and the adjoint method was compared for various structures with and without lumping. The results were reported in two papers (Akgun et al., 1998a and 1999). It is desirable to optimize topology of an aerospace structure subject to a large number of damage scenarios so that a damage tolerant structure is obtained. Including damage scenarios in the design procedure is critical in order to avoid large mass penalties at later stages (Haftka et al., 1983). A common method for topology optimization is that of compliance minimization (Bendsoe, 1995) which has not been used for damage tolerant design. In the present work, topology optimization is treated as a conventional problem aiming to minimize the weight subject to stress constraints. Multiple damage configurations (scenarios) are considered. Each configuration has its own structural stiffness matrix and, normally, requires factoring of the matrix and solution of the system of equations. Damage that is expected to be tolerated is local and represents a small change in the stiffness matrix compared to the baseline (undamaged) structure. The exact solution to a slightly modified set of equations can be obtained from the baseline solution economically without actually solving the modified system.. Shennan-Morrison-Woodbury (SMW) formulas are matrix update formulas that allow this (Akgun et al., 1998b). SMW formulas were therefore used here to compute adjoint displacements for sensitivity computation and structural displacements in damaged configurations.
Understanding radiation effects on avalanche photodiodes (APDs) is important because they are used in several applications involving harsh radiation environments. APDs are used as photosensors in applications where speed and detection efficiency are critical. Proton irradiation experiments on a commercial off-the-shelf APD demonstrated that the irradiation flux and applied reverse bias have a strong influence on the severity of radiation effects. This is measured using the ion beam induced charge (IBIC) technique in which charge collection efficiency (CCE) describes the signal response from a device. CCE can degrade substantially due to radiation damage, but recent measurements show that certain combinations of irradiation flux and reverse bias can lead to increases in CCE up to 186% ± 24% for irradiations with 2 MeV protons at a fluence of 6.4 × 10 11 cm –2 . This defect-enhanced charge multiplication (DECM) only appeared when the reverse bias during irradiation ranged from 170 to 1830 V out of a maximum operating bias of 2000 V and the proton flux ranged from 9.8 × 10 7 to 3.4 × 10 9 cm –2 s –1 . Furthermore values outside of either range led to losses in CCE. It is expected that DECM should be encountered in other devices, especially those with sufficiently high electric fields to cause impact ionization.
In this paper, an extended/generalized finite element method (XFEM/GFEM) for simulating quasistatic crack growth based on a phase-field method is presented. The method relies on approximations to solutions associated with two different scales: a global scale, that is, structural and discretized with a coarse mesh, and a local scale encapsulating the fractured region, that is, discretized with a fine mesh. A stable XFEM/GFEM is employed to embed the displacement and damage fields at the global scale. The proposed method accommodates approximation spaces that evolve between load steps, while preserving a fixed background mesh for the structural problem. In addition, a prediction-correction algorithm is employed to facilitate the dynamic evolution of the confined crack regions within a load step. Several numerical examples of benchmark problems in two- and three-dimensional quasistatic fracture are provided to demonstrate the approach.