Reliability modeling for safety-critical software

Software reliability predictions can increase trust in the reliability of safety critical software such as the NASA Space Shuttle Primary Avionics Software System (Shuttle flight software). This objective was achieved using a novel approach to integrate software-safety criteria, risk analysis, reliability prediction, and stopping rules for testing. This approach applies to other safety-critical software. The authors cover only the safety of the software in a safety-critical system. The hardware and human-operator components of such systems are not explicitly modeled nor are the hardware and operator-induced software failures. The concern is with reducing the risk of all failures attributed to software. Thus, safety refers to software-safety and not to system-safety. By improving the software reliability, where the reliability measurements and predictions are directly related to mission and crew safety, they contribute to system safety. Software reliability models provide one of several tools that software managers of the Shuttle flight software are using to assure that the software meets required safety goals. Other tools are inspections, software reviews, testing, change control boards, and perhaps most important-experience and judgement     

Reliability modeling of flexible manufacturing systems

This paper presents a modeling approach for assessing the reliability of flexible manufacturing systems. FMSs are very difficult to model by analytical methods, because of their complexity. Many of their parameters, especially equipment failure and repair rates, exhibit great uncertainty. The proposed approach owes its success to an effective heuristic method called Group Method of Data Handling. The algorithm has proven very useful for modeling complex nonlinear systems with large number of parameters and little collected data. By combining it with analytical methods, models that closely predict the FMS output are produced that become valuable tools for evaluating FMSs during their design and operation.     

Reliability modeling algorithms for a class of large repairable systems

The reliability performance of some multistate large repairable systems cannot be described by a dichotomy of success and failure but by probability and frequency distribution of several levels of performance, algorithms for reliability modeling of such systems consisting of several units, each contributing a finite amount to the total system capacity. The first algorithm describes system model building by the sequential addition of units and the second one can be used for taking off particular units from the system model. The algorithms are fast and can be easily implemented in a computer program.     

Reliability modeling of life-critical, real-time systems

We discuss the role of modeling in the design and validation of life-critical, real-time systems. The basics of Markov, Markov reward, and stochastic reward net models are covered. An example of a nuclear power plant cooling system is developed in detail. Multilevel models, model calibration, and model validation are also discussed     

Reliability modeling of hardware/software systems

This paper uses a single model to analyze the effects of both hardware and software on system reliability. A unified model of hardware and software reliability is developed using Markov modeling. Then the effect of hardware and software failures is studied using the model. The model incorporates concepts from both hardware and software reliability modeling. Examples of both simplex (nonredundant) and redundant architectures are analyzed using the model     

Reliability modeling and performance of variable link-capacitynetworks

The discussion by R. Schanzer (see ibid., vol.44, p.620-1, 1995) tries to correct the algorithms of P.K. Varshney, et al. (see ibid., vol.43, p.378-82, 1994) and K.K Aggarwal (see ibid., vol.37, p.65-9, 1988). But Schanzer doesn't explain why those algorithms have difficulty in calculating the maximum flow. This paper explains the problem and gives a correction of the algorithm so that the basic problem can be solved     

Reliability modeling and performance evaluation of variablelink-capacity networks

This paper presents a composite performance index for communication networks with variable link-capacities. This index is based on link reliabilities and multiple-capacity link-states. Source-to-terminal success is the ability to provide connectivity with a certain traffic-carrying capacity. This index is useful for determining the performance of networks with links operating with residual traffic-carrying capacity and gives a good idea of the available resources for a particular s-t connection. An algorithm is given to evaluate the composite performance index     

Reliability growth modeling for in-service electronic systems considering latent failure modes

A latent failure mode is a type of failure that may not occur until the system has operated in the field for a certain period of time. Predicting latent failures is often difficult, but it has a great importance for reliability management in terms of system maintenance and warranty services. This paper proposes a stochastic model to predict the reliability growth for field or in-service electronic systems considering latent failures. The proposed model can be applied to electronics industries where extended in-house reliability testing cannot be implemented due to the tight design schedule. Based on the new method, the product management can proactively implement corrective actions against key failure modes using relevant engineering resources. A discussion between the effectiveness of corrective actions and the associated cost is also provided. Finally, field failure data collected from a fleet of automatic test equipment are used to demonstrate the applicability and performance of the model.     

Reliability modeling and assessment of the Star-Graph networks

The reliability of the Star Graph architecture is discussed. The robustness of the Star Graph network under node failures, link failures, and combined node and link failures is shown. The degradation of the Star Graph into Substar Graphs is used as the measure of system effectiveness in the face of failures. Models are provided for each of the failure and re-mapping modes evaluated herein, and the resilience of the Star Graph to failures is emphasized. This paper defines failure of a Star Graph as being when no fault-free (n - 1)-substars remain operational and the intermediate states are defined by the number of (n - 1)-substars that remain operational. A powerful tool (re-mapping) is introduced in which the number of operational (n 1)-substars can be maintained for longer periods, thus improving the overall MTTF (mean time to failure). For comparison the results of a similar reliability analysis of the hypercube is shown. The comparisons are considered conservative due to the failure model used herein for the star graph. One might apply re-mapping to hypercubes; while it would improve the overall MTTF of hypercubes, the hypercubes would still have an appreciably poorer performance than star graphs     

Reliability and lifetime modeling of wireless sensor nodes

The accuracy of system reliability analysis depends not only on system-level model construction, but also on realistic estimation of failure parameters at the component-level. In this paper, we model and evaluate the reliability and lifetime of a wireless sensor node under three typical working scenarios, contributing toward the accurate reliability analysis of wireless sensor network systems. According to the medium access control (MAC) protocols, the three working scenarios are defined based on the sensor node modes (sleep and active) and the mechanism of alternating between the modes. Reliability and lifetime of wireless sensor nodes under these three scenarios are illustrated and compared through numerical examples.     

Reliability modeling of engineered barrier systems for nuclear waste: A conditional approach

The lifetime of the Engineered Barrier System (EBS) used for containment of high-level radioactive waste will play an important role in controlling the cumulative release of radionuclides from a geological repository. Essentially, an EBS has two major components: a metal barrier and the waste form (cladding). Since any suitable site is above the static water table, the decay heat generated from this waste is expected to keep the surface temperature of a canister above the boiling point of water for a T random time period. Assuming the Weibull lifetime distribution on each component, we use the conditional approach to derive the lifetime distribution of the EBS. In our model, the oxidization process of the metal barrier (i.e. the lifetime of the metal barrier) starts after this time T and the lifetime of the cladding starts after the lifetime of the metal barrier     

Reliability modeling of on-surface transit systems with human errors

This paper presents two newly developed Markov models representing on-surface transportation systems subject to hardware failures and human errors. Transit system reliability, steady state availability, mean time to failure (MTTF) and variance of time to failure formulas are developed. Selective plots are shown for each model.     

Reliability assessment and hygroswelling modeling of FCBGA with no-flow underfill

In the flip-chip ball grid array (FCBGA) assembly process, no-flow underfill has the advantage over traditional capillary-flow underfill on shorter cycle time. Reliability tests are performed on both unmolded and molded FCBGA with three different types of no-flow underfill materials. The JEDEC Level-3 (JL3) moisture preconditioning, followed by reflow and pressure cooker test (PCT) is found to be a critical test for failures of underbump metallization (UBM) opening and underfill/die delamination. In this paper, various types of modeling techniques are applied to analyze the FCBGA-8×8 mm on moisture distribution, hygroswelling behavior, and thermomechanical stress. For moisture diffusion modeling, thermal-moisture analogy is used to calculate the degree of moisture saturation in the multi-material system of FCBGA. The local moisture concentration along the critical interface, e.g. die/underfill, is critical for delamination, because the moisture weakens the interfacial adhesion strength, generates internal vapor pressure during reflow, and induces tensile hygroswelling stress on UBM during PCT. The results of moisture distribution can be used as loading input for the subsequent hygroswelling modeling. The magnitude of hygroswelling stress acting on UBM is found to be greater than the thermal stress induced during reflow, both in tensile mode which may cause the UBM-opening failure. Underfill with lower saturated moisture concentration (C_sat) and coefficient of moisture expansion (CME) are found to induce lower UBM stress and has better reliability results. Molded package generally has higher stress level than unmolded package. Parametric studies are performed to study the effects of no-flow underfill materials, package type (molded vs. unmolded), die thickness, and substrate size on the stresses of UBM during reflow and PCT.     

Reliability modeling and planning of energy harvesting based on uncertainty theory

Energy harvesting network is a new form of computer networks.It can convert the environmental energy into usable electric energy,and supply the electrical energy as a primary or secondary power source to the electronic device for network communication.However,the energy harvesting process has great volatility and uncertainty,the traditional analytical method based on probability distribution function to describe the energy collection process can not accurately simulate the actual situation,resulting in higher depletion probability of nodes,then the reliability cannot be guaranteed as a result.For this,the energy harvesting reliability of energy harvesting nodes was defined,represented with the degree of normal operation,respectively set up the node reliability models with no battery and infinite battery.As an example for maximum node achievable rate,the uncertain multilevel programming model based on node reliability was put forward,then the network efficiency was improved under the premise of ensuring node reliability.An energy average allocation (EAA) algorithm was proposed and the upper bound of competitive ratio of the algorithm was proved theoretically.Finally,the actual wind power data was taken as an example to verify the feasibility and effectiveness of the proposed model and method.     

Reliability modeling of multi-state degraded systems with multi-competing failures and random shocks

In this paper, we develop a generalized multi-state degraded system reliability model subject to multiple competing failure processes, including two degradation processes, and random shocks. The operating condition of the multi-state systems is characterized by a finite number of states. We also present a methodology to generate the system states when there are multi-failure processes. The model can be used not only to determine the reliability of the degraded systems in the context of multi-state functions, but also to obtain the states of the systems by calculating the system state probabilities. Several numerical examples are given to illustrate the concepts.     

Reliability modeling of TMR computer systems with repair and common mode failures

The effect of repair and common-mode failures on the reliability and mean up time of a TMR computer configuration is analyzed and shown to be significant.     

扬声器的可靠性和可靠性试验

阐述了扬声器的可靠性和可靠性试验的主要问题,从试验目的、试验应力和失效数据等方面讨论了扬声器可靠性和可靠性试验,在扬声器的设计和制造阶段进行可靠性工作十分重要。     

Reliability modeling on a MOSFET power package based on embedded die technology

Embedding of discrete semiconductors into substrates has the advantages of achieving high degree of miniaturization, good electrical performance and possible low cost. A MOSFET power package based on the embedded die technology was developed and the demonstrators were built. To reduce cost and time-to-market, thermo-mechanical virtual prototyping is applied to support the package development. 2D and 3D parametric FE models were established to conduct numerical simulations to investigate the thermo-mechanical reliability performance under packaging processes and test conditions. The package design and material variations, such as the thicknesses of the Cu layer and the resin in the RCC foil, the Bond Line Thickness (BLT), the thickness and material properties of prepreg, via dimensions and via-filling, were included in the parametric models. The root cause for die cracking, delamination between the interface die/RCC foil, and cracking of Cu vias were analyzed based on the simulation results. Verification of the modeling results was conducted through comparison with the test results. The results indicate that the prediction from the FE modeling matches reasonably well with the test results.     

Reliability issues and modeling of Flash and post-Flash memory (Invited Paper)

Flash memory, in particular NAND, has been an enabling technology for portable applications for the last two decades. The strength of Flash is its excellent scaling capability, allowing an ever increasing density at a decreasing cost and maintained reliability. However, the geometrical scaling of the cell exacerbates charge loss and fluctuation effects. On the other hand, new post-Flash memory technologies are being proposed, with different storage concepts and reliability physics. This review discusses the major reliability issues for Flash, with emphasis on the physical mechanisms and modeling. The reliability of charge trap and resistive memories, such as phase change and resistive switching memories, is addressed.