Fail-safe Structure Research Articles

Multiresolution and multimaterial topology optimization of fail-safe structures under B-spline spaces

Multiresolution and multimaterial topology optimization of fail-safe structures under B-spline spaces

Adaptive topology optimization of fail-safe truss structures

Avoidance of disproportionate and progressive collapse, often termed ‘fail-safe design’, is a key consideration in the design of buildings and infrastructure. This paper addresses the problem of fail-safe truss topology optimization in the setting of plastic design, where damage is defined as a moveable circular region in which members are considered to have zero strength for that particular load case. A rigorous and computationally efficient iterative solution strategy is employed in both the dual (member adding) and primal (damage-case adding) problems simultaneously, which allows cases of high complexity and many damage cases (maximum of 16290 potential members and 16291 damage cases) to be solved to the global optimum. Common member-based damage definitions (e.g. damage to any one member) are shown to be highly dependent on the nodal grid; in the limiting case completely negating the effect of the fail-safe constraints. The method proposed in this article does not have such limitations, enabling a more sophisticated and robust treatment of fail-safe design. Moreover, the global minimization and high resolutions create new benchmarks for the least-material designs of ‘fail-safe’ structures using rigid-plastic materials. A number of example structures are considered (short cantilever, square cantilever, multi-span truss), and the effects of damage radius, location, and structure rationalisation are discussed.

Optimal fail-safe truss structures: new solutions and uncommon characteristics

Optimal fail-safe truss structures: new solutions and uncommon characteristics

Experimental modal analysis of glass and laminated glass large panels with EVA or PVB interlayer at room temperature

Laminated glass is used for fail-safe structures in many fields of engineering. It contains a polymeric interlayer that improves the brittle glass behavior after fracture, provides damping, increases impact resistance, and at the same time maintains transparency. This paper examines the effect of the type of the interlayer on laminated glass oscillation using a roving hammer test. It also compares the modal response of the laminated glass before and after the low-velocity impact. The experimental modal analysis is validated by numerical modal analysis and using a different experimental methodology. This contribution discusses natural frequencies and damping ratios affecting the impact response and the reduction of noise and vibrations. It is found that the inserted polymer foils increased the damping and the impact resistance of the transparent plate. The interlayer with a higher ratio between loss and storage modulus showed higher damping and thus energy dissipation potential. No significant difference was measured in the natural frequencies of laminated glass before and after low-velocity impact. Inferences drawn from this study can be used by engineers, architects, and contractors when selecting suitable panels for applications such as windshields or curtain walls.

Risk-averse approach for topology optimization of fail-safe structures using the level-set method

Risk-averse approach for topology optimization of fail-safe structures using the level-set method

Mechanics of air-inflated 3D distance fabric

3D distance fabrics are modern and promising material for lightweight inflatable structures. The applications are used in sport, boats, tents, construction, military etc. Its advantages are large load capacity per unit weight, stiffness dependent on pressurized air, fail-safe structure. However, the mechanics of inflated fabric panel is not still described enough. This paper gives basic theory and its experimental verification about mechanical behaviour of distance fabrics. The mathematical model of air-inflated distance fabric panel is created based on analytical theory of cylindrical bending of plates. Material data of the fabric required for performing computations of the model are determined from tensile tests. The reliability of the analytical model is experimentally verified. For that purpose the air-inflated fabric panel was made and tested. Results obtained both experimentally and analytically are compared and discussed. The experiment proves the validity of the mathematical model and allows us to predict the behaviour of distance fabrics.

Fail-safe topology optimization of continuum structures with fundamental frequency constraints based on the ICM method

It is an important topic to improve the redundancy of optimized configuration to resist the local failure in topology optimization of continuum structures. Such a fail-safe topology optimization problem has been solved effectively in the field of statics. In this paper, the fail-safe topology optimization problem is extended to the field of frequency topology optimization. Based on the independent continuous mapping (ICM) method, the model of fail-safe topology optimization is established with the objective of minimal weight integrating with the discrete condition of topological variables and the constraint of the fundamental frequency. The fail-safe optimization model established above is substituted by a sequence of subproblems in the form of the quadratic program with exact second-order information and solved efficiently by the dual sequence quadratic programming (DSQP) algorithm. The numerical result reveals that the optimized fail-safe structure has more complex configuration and preserved materials than the structure obtained from the traditional frequency topology optimization, which means that the optimized fail-safe structure has higher redundancy. Moreover, the optimized fail-safe structure guarantees that the natural frequency meets the constraint of fundamental frequency when the local failure occurs, which can avoid the structural frequency to be sensitive to local failure. The fail-safe optimization topology model is proved effective and feasible by four numerical examples.

Probability-damage approach for fail-safe design optimization (PDFSO)

Fail-safe design often leads to oversized structures as the design must be able to behave properly for the different accidental situations that could undergo throughout their lifespan. The existing research about structural optimization applied to fail-safe design does not contemplate the idea of having accidental situations with different probabilities of occurrence. This means that the structure must satisfy the design constraints in the damaged structure regardless of whether one accidental situation is much more likely than another. The objective of this research is to formulate a new optimization strategy to get fail-safe structures with minimum weight taking into account the available data about the probability of occurrence associated to each partial collapse. A multi-model probabilistic optimization problem is defined and applied to two structures: a 2D truss structure with stress constraints as well as the tail section of an aircraft fuselage with stress and buckling constraints.

Cable Bacteria: An Ordered and Fail‐Safe Electrical Network in Cable Bacteria (Adv. Biosys. 7/2020)

Long before the age of microelectronics, a group of filamentous microorganisms named cable bacteria developed an electrical network within their own cell structure. In article number 2000006, Jean V. Manca and co-workers present the local electrical pathways for cable bacteria using conductive atomic force microscopy, showing a fail-safe electrical structure conducted by parallel and electrically interconnected biological fibers.

The robust fail-safe topological designs based on the von Mises stress

For large-scale equipment, e.g. aerospace and architecture industry, it is valuable to guarantee that one structure could survive partial damages. Due to the location of the damage is unknown in prior, results in a high number of failure scenarios to be calculated when considering fail-safe requirement in topology optimization. In this article, we propose an efficient continuum topology optimization method on the basis of the design philosophy of robust fail-safe structure. A number of patches with predefined shapes are used to simulate the material failure. The material properties of damaged models are interpolated by von Mises stress to construct the well-posed optimization model. The damaged compliance for the worst failure case is set as the optimization objective, and the KS function is adopted to approximate the non-differentiable max-operator. A computationally efficient sensitivity formulation is derived via the adjoint method. To suppress the highly nonlinear stress behavior and the phenomenon of optimization oscillation, an extended variable update scheme within the framework of Optimality Criteria (OC) method is developed. Representative benchmarks show that the presented strategy has the effectiveness at yielding the fail-safe structure by using acceptable computational cost.

Effect of laser beam welded reinforcement on integral skin panel fatigue life

In this paper, numerical analyses of fatigue crack growth in integral skin-stringer panel produced by means of laser beam welding (LBW) are presented along with fatigue results verified by previously conducted experiments. Skin-stringer panel is fail-safe structure widely used in aircraft industry, which requires a good estimate of fatigue life after crack initiation. In the past, experimental work was the only successful method for fatigue life estimation of complex damaged structure, but nowadays researches have powerful numerical tools, such as extended finite element method (XFEM), for three-dimensional crack growth analysis. In research presented here, XFEM was initially used for crack growth simulation in simple flat plate made of aluminium 6156 T6 and 6156 T4 for the purpose of procedure verification, since fatigue life for simple plate was known from experiment. Then, XFEM was used to simulate fatigue crack growth in the panel reinforced with four stringers. Fatigue life obtained on the basis of calculated stress intensity factors (SIFS) along the crack fronts on LBW skin-stringer panels was, as expected, significantly longer than experimentally measured life of simple flat plate. Finally, several numerical simulations were performed in order to analyse the influence of mesh size on accuracy of estimated fatigue life of damaged LBW skin panels. For that purpose, average element sizes of 1, 2 and 4 mm were used.

Fatigue Analysis of a Panel Consisting of Window Cutout and Frames in the Fuselage of a Transport Airframe

Aircraft structure is the symbolic representation of high performance where functional requirements demand light weight and, therefore, high operating stresses. An efficient structural component must have three primary attributes; namely, the ability to perform its intended function, adequate service life and the capability of being produced at reasonable cost. To ensure the safety of aircraft structures, life estimation analysis is essential. This paper focuses its attention on designing a fail-safe fuselage structure. The damage most frequently associated with the structural integrity of the fuselage are longitudinal cracks under high hoop stresses induced by cabin pressurization of the fuselage. The analysis of these types of cracks is complex, first due to the complex structural configuration (i.e. frames, skin Longerons and crack stopper straps) and secondly due to the influence of the curvature of the shell. Various analytical and empirical approaches have been used to study the fatigue life capability of the fuselage structure. In this paper, fatigue analysis of a panel consisting of window cut out and frames in the fuselage of a transport airframe are carried out through FEA method of analysing.

Correlation between residual stresses and bending in functional electroceramic-based MEMS actuator

Micro-electro-mechanical systems (MEMS) technology can offer a viable alternative to realize miniaturized and less expensive actuators for deformable mirror in adaptive optics to obtain high resolution retinal imaging. During fabrication of such devices, functional multilayered thin films are deposited at elevated temperatures. These films are therefore subjected to residual stresses which may result in bending of the structure. The bending thus occurred may lead to failure at interfaces between films. A successful fabrication of device therefore relies on the engineering justification of multi-structured device design and growth parameters used in fabrication. In this paper, we present the design of a piezoelectric (ceramic) thin film based MEMS actuator for deformable mirror used in retinal imaging. A proto-type piezoelectric thin film structure of Pt/PZT/SRO/Pt/γ-Al2O3 has been epitaxially fabricated on Si (111) substrate. Advanced 3D finite element simulations were conducted to correlate the bending of fabricated structure with residual stresses. A smart alternative design was also proposed employing an extra layer of Al–Si (1%) in the diaphragm region. Simulation results predict a failsafe structure when the thickness of extra Al–Si (1%) layer is tailored to an optimal thickness. The outcome of this research can be used to overcome the challenge encountered (bending due to residual stresses) to obtain a failsafe MEMS actuator for deformable mirror.

Topology optimization of fail-safe structures using a simplified local damage model

Topology optimization of mechanical structures often leads to efficient designs which resemble statically determinate structures. These economical structures are especially vulnerable to local loss of stiffness due to material failure. This paper therefore addresses local failure of continuum structures in topology optimization in order to design fail-safe structures which remain operable in a damaged state. A simplified model for local failure in continuum structures is adopted in the robust approach. The complex phenomenon of local failure is modeled by removal of material stiffness in patches with a fixed shape. The damage scenarios are taken into account by means of a minimax formulation of the optimization problem which minimizes the worst case performance. The detrimental influence of local failure on the nominal design is demonstrated in two representative examples: a cantilever beam optimized for minimum compliance and a compliant mechanism. The robust approach is applied successfully in the design of fail-safe alternatives for the structures in these examples.

Deconstructing the Toolkit: Creativity and Risk in the NHS Workforce

Deconstructing the Toolkit explores the current desire for toolkits that promise failsafe structures to facilitate creative success. The paper examines this cultural phenomenon within the context of the risk-averse workplace-with particular focus on the NHS. The writers draw on Derrida and deconstructionism to reflect upon the principles of creativity and the possibilities for being creative within the workplace. Through reference to The Extra Mile project facilitated by Open Art, the paper examines the importance of engaging with an aesthetic of creativity and embracing a more holistic approach to the problems and potential of the creative process.

Failsafe Control Methods for EVs with the Failsafe Structure Driven by Front and Rear Wheels Independently

This paper describes failsafe control methods for electric vehicles (EVs) with the failsafe structure in which front and rear wheels are driven independently. Based on failure-diagnosis results, the failsafe control is done by dividing fault states into two types, i.e. a slight failure such as a current or a speed sensor failure and a serious failure such as an inverter or a motor failure. For the latter, the EV keeps on driving with only the healthy drive system by separating the drive system including the failed inverter or motor. On the other hand, for the former, a fault tolerant control is performed that keeps on driving while compensating for the function of the failed sensors so that the drive performance before failure can be maintained as much as possible. Effectiveness of the proposed methods is verified through simulations and experiments using bench test equipment which is equivalent to the actual EV drive systems and a prototype EV.

Structural Health Monitoring of an Advanced Grid Structure with Embedded Fiber Bragg Grating Sensors

The authors focus on the construction of a structural health monitoring (SHM) system with an advanced grid structure (AGS) made of carbon-fiber reinforced plastic (CFRP). AGS is often applied to aerospace structures because the ribs carry only axial forces in the carbon fiber direction, making AGS structurally effective and lightweight, and because the repetition of many ribs in the AGS composition results in damage tolerance. The failure of a single rib hardly affects the fracture of the whole structure, making AGS a fail-safe structure. In this research, the authors have embedded multiplexed-fiber Bragg grating (FBG) sensors into an AGS rib in the longitudinal direction to measure mechanical strains of all ribs in order to detect the existence and regions of AGS rib fractures. Monitoring the change in rib-longitudinal strains is the most effective SHM system for AGS. To confirm the proposal, the authors explore the following. First, various damage characteristics under low-velocity impact loading are investigated and it is verified that partial rib cracks are the most typical damage in AGS. An AGS is then fabricated with embedded FBG sensors and verified that the SHM system is able to measure all rib strains. Subsequently, it is analytically determined that the change in longitudinal-rib strains is the most appropriate mechanical feature for damage detection. Moreover, a statistical outlier analysis is introduced into the SHM system for automatic damage detection. Finally, AGS is established with the SHM system and verified experimentally. Results confirm that the existence of damage and its regions in AGS can be detected with the proposed SHM system.

ロボットとの接触防止の為の安全センサの一構成法(G15-1 センシング・認識,G15 ロボティクス・メカトロニクス部門)

In the situation that man works in the work space of the robot, the possibility of the accident by the contact of the robot and man cannot be canceled no matter how it provides with the emergency, stop means of the robot. Then, the interlock to urgent stop by the contact sensor to secure safety to contact accident is the examined in this study. The interlock system which rapidly stops the robot becomes possible detecting contact with man by fully covering the robot arm with the contact sensor of the piezo film type. In this research, the breakdown characteristic of the piezo film sensor is examined to achieve the Fail-safe structure that the robot stopped when the sensor in this system broke down, and the response of the system when breaking down is also examined.

Failure Time Prediction of Deteriorating Fail-Safe Structures

Structural evaluation and design have been dominated by component safety checks. In fact, current reliability-based codes for buildings and bridges are largely limited to individual structural component checks and do not generally include requirements for system reliability. Also, these codes do not consider the potential damaged states of a structural system and the ability of the damaged system to continue to carry loads. Furthermore, current codes do not entail the prediction of the failure time of deteriorating structural systems under time-varying loads. In this study, the reliability of deteriorating fail-safe structures is investigated using a time-variant parallel system reliability approach in which both load and resistance are time dependent. Monte Carlo simulation is used to find the cumulative-time system failure probability. Numerical examples are presented to illustrate the effects of various parameters such as variabilities in live loads, live load occurrence rate, live to dead load ratio, strength loss rate, resistance correlation, and number of degrading members on the cumulative-time failure probability of a deteriorating fail-safe system. Postfailure behavior of components and load redistribution effects are also considered. The results can be used to better predict the failure time of deteriorating fail-safe structures, such as redundant reinforced concrete bridges under corrosion attack, and to develop optimal lifetime reliability-based maintenance strategies for these structures.

Bayesian Reliability Analysis for Non-Periodic Inspection with Estimation of Uncertain Parameters

The present study concentrates on the development of the Bayesian reliability analysis for estimating appropriate values of several uncertain parameters in probability distributions and generating appropriate non-periodic structural inspection schedules using small sample data gathered during in-service inspections. A pressurized fuselage structure of transport-type aircraft with multiple fatigue-critical elements is accepted as a structural model in this analysis. This element is a multiple component of two-bay fail-safe structure, designed by the damage tolerance principle, which consists of three frames and a skin panel subjected to cyclic stress due to differential pressure. Fatigue cracks are initiated and propagated from a hole for a rivet to connect the skin panel to the center frame. Probabilistic factors considered in this model are fatigue crack initiation and propagation, failure rates before and after crack initiation, yield stress, fracture toughness, cyclic stress range and crack detection capability of detailed visual inspection. Uncertain parameters estimated from inspection data such as the number of detected cracks, crack sizes and whether or not failures were detected are a scale parameter in a probability density function of fatigue crack initiation and a parameter in a simplified fatigue crack propagation equation. Both parameters can not be a priori estimated because of the paucity of pertinent data. Monte Carlo simulation techniques are utilized in order to generate a failure process in the structural element and to evaluate the validity of the proposed Bayesian reliability analysis.