Tolerant Design Research Articles

Fatigue Life Analysis of Railway Axles under Pre-crack Conditions

This paper takes the wheelset of a certain type of EMU as the research object and checks the strength of the axle according to the standard, and the most dangerous section of the axle is determined to be 35 mm away from the inner edge of the wheel seat. A crack with a depth of 1.2 mm was prefabricated by an electric spark in this position, and the crack was extended to a semi-elliptic crack with a depth of 2 mm by a fatigue test. The remaining service life of the non-damaged axle and the defective axle were analyzed based on the cumulative damage theory and the damage tolerance design method.

Probability of detection curve for the automatic visual inspection of steel bridges

AbstractThe damage tolerant design philosophy is based on periodical inspections and provides safe bridge operation preventing fatigue cracks from growing up to a critical size. It is possible to optimize the management costs of a bridge throughout its life by designing the inspection frequency, which depends on the capabilities of the inspection method. However, such optimization requires knowledge about the performance of inspections that are envisioned to take place during the use of the bridge. Regular visual inspections is the most frequently applied type of inspection of bridge structures. Recent advances in computer vision technologies provide a strong basis for the development of automatic damage detection systems that can support regular visual inspection, thus increasing the reliability of the inspection. Several automatic crack detection systems have been developed in the past years. However, the performances of such systems have not been evaluated in the way as for traditional non‐destructive inspection methods, i.e. in terms of probability of detection curves and detectability limits. This restricts the applicability of automatic visual inspections for inspection planning and damage tolerant design. This paper proposes an encoder‐decoder neural network for segmentation of cracks on images of steel bridges. A probability of detection curve is calculated for this neural network.

An Optimal Tolerance Design Approach of Robot Manipulators for Positioning Accuracy Reliability

An Optimal Tolerance Design Approach of Robot Manipulators for Positioning Accuracy Reliability

High cycle fatigue resistance of laser powder bed fused Ti–6Al–4V alloys with processing-induced porosity: Towards damage-tolerant design of printed components

Three groups of Ti–6Al–4V specimens were printed on an industrial laser powder bed fusion system using three volumetric energy densities (47, 38 and 30 J/mm3), called High, Optimal and Low (HED, OED and LED), and subjected to stress relief and annealing heat treatments. The reference OED group had the smallest amount of porosity <0.005%, while the two other groups (HED and LED) had similar levels of porosity (0.03–0.05%), but formed by flaws of different nature: gas pores (HED) and lack-of-fusion defects (LED). First, chemical composition, microstructure and porosity features of each group of specimens were analyzed. Then, uniaxial tensile testing, axial fatigue testing, fractography analysis and fatigue crack growth testing were carried out. Similar chemical compositions and bi-modal microstructures were observed in all the specimens. Micro-computed tomography (μCT) confirmed the targeted porosities and types of pores for each group of specimens, with only the LED specimens having a significant number of pores larger than 0.07 mm. Tensile properties were similar for all the specimens with the exception of elongation to failure, which was significantly lower for the LED specimens as compared to the HED and OED specimens (∼11 vs. ∼14%). Fatigue testing of the HED, OED and LED specimens showed runout (107) stress ranges (Δσ) of, respectively, 450, 495 and 360 MPa, while fatigue crack growth testing resulted in a threshold stress intensity value of ΔK = 3.9 MPa m½ for all the specimens. A Kitagawa-Takahashi diagram was built as a function of the μCT-measured defect size and showed to be an appropriate while conservative tool for the defect tolerant design of Ti–6Al–4V LPBF components. A strong influence of the defect size and proximity to the surface on the fatigue behavior was observed, while the defect shape was shown to have little incidence on this property. Overall, this study showed that the influence of pore size on the fatigue resistance becomes particularly significant once a certain pore size threshold (√area ≈0.2 mm) is exceeded, and that this eventuality coincides with a ∼20% decrease in the volumetric laser fusion energy density as compared to its optimum value.

A physics-based defect tolerant design approach to predict the tensile performance of aluminium alloys with a defect

Inherent manufacturing defects are observed in additively manufactured and casted metallic alloys. During loading, the stress concentration due to defect results in poor tensile ductility and fatigue performance. A physics-based defect tolerant design approach is used in the present work to calculate the uniaxial tensile performance of cast ADC12 Aluminum alloys. The proposed model elucidates the correlation between tensile ductility and the dimensions of material defects. It derives a material constant referred to as the critical defect size, which is determined through a combination of uniaxial tensile testing on specimens with defects and employing finite element simulations. The proposed approach calculates well the tensile properties such as complete tensile stress–strain curve, ultimate tensile strength, and uniaxial tensile elongation.

Fatigue Crack Propagation in Pearlitic Steel under Pressurized Gaseous Hydrogen: Influences of Microstructure Size and Strength Level

For the wall-thickness reduction of the components destined for pressurized gaseous hydrogen, widespread use of high-strength martensitic steels has long been desired. However, their strong susceptibility to hydrogen-assisted fatigue crack growth (HA-FCG) is still limiting their proactive applications. Here, we instead focused on pearlite as another potential reinforcing agent for the development of new hydrogen-compatible steels with acceptable cost performance. Fatigue crack growth (FCG) behavior of three eutectoid steels with different microstructure sizes (i.e., ferrite/cementite interlamellar spacing, colony and block sizes) and strength levels was investigated in a 90 MPa hydrogen gas, an essential evaluation when attempting to perform a defect tolerant design of the components used for high-pressure gases.

Scaled fatigue cracks under service loads

Scaled experimentation is a powerful engineering tool yet its application to fatigue is limited by significant changes in behaviour with scale. The recent discovery of new similitude rules however opens new possibilities that are explored in this work through numerical experimentation for industrially representative fatigue-crack growth scenarios. It is shown for the first time, how the geometric size effects present in mixed mode fatigue tests are eliminated by performing two appropriately designed scaled experiments. The first order finite similitude theory is applied to mixed mode (modes I and II) fatigue crack growth in three case studies, viz., compact tension shear (CTS) specimen, wing fuselage attachment lug, and a T-joint with an inclined semi elliptical crack. Both planar and non-planar crack growth feature, along with surface and through thickness cracks. Low and high cycle fatigue (up to circa 60,000 cycles) is examined for three different materials (Al-6061 T6 alloy, structural steel, and AISI 316 stainless steel) under a variety of load ratios. The new rules return near exact crack-path predictions whereas lifecycle predictions have errors ranging between 1 % and 9 %. Paris law constants C and m are predicted with up to 99.9 % accuracy supporting the theory that Paris law is a first order similitude rule. Geometric size effects afflicting industrial type scaled-fatigue studies employing a damage tolerant design approach are confirmed to be eliminated on combination of information from two appropriately designed scaled models.

AN APPROACH FOR THE INCLUSION OF LOADING CONDITIONS IN A POLYHEDRAL-BASED METHOD FOR EARLY VARIATION MANAGEMENT

AbstractThe variation management and product quality processes are important tasks to guarantee the assemblability of the systems, the scrap reduction and to avoid delays on production and launching. The compound of activities in Geometric Dimensioning and Tolerancing (GD&amp;T) are necessary, especially in the early design stages, to take into account variations of different nature and from different sources. In this paper, an approach for considering the loading conditions in a polyhedral-based approach in tolerancing design is presented. The load boundary conditions are represented as additional displacement restrictions in the deviation space. The restrictions imposed by the physical limits of a system, the ones coming from the loading conditions and the degrees of freedom (DoF) can be all described and represented with a single polyhedron operand. The approach is illustrated using a simplified 2-D model for both ideal and non-ideal geometry. A 3-D model describing an unilateral contact is presented as a case study using Skin Model Shapes. By taking into account geometrical form defects, external loads, and the kinematics of the system, its sensitivity to variations can be reduced even from early design stages.

Engineered metal coverage of anode catalyst layer enhancing cell reversal tolerance for proton exchange membrane fuel cells

Anode cell reversal, which is caused by fuel starvation, poses a great threat to the durability of proton exchange membrane fuel cells. Commercially, iridium oxide or iridium is applied to boost oxygen evolution reaction, which alleviates carbon corrosion and protects the catalyst layer structure. However, the key factors that affect the anti-reversal ability and the interaction between Pt, Ir, and carbon support are still unclear. Hence, we systematically studied the performance using three typical carbon supports with three metal contents and different metal deposition orders by experiments and model calculations. A new parameter, “relative metal coverage”, is put forward to evaluate and predict the anti-reversal ability, showing higher relative metal coverage results in a longer reversal time and lower polarization performance degradation rate. Typically, only a 15.5% polarization performance loss after 1700 mins reversal time when the relative metal coverage of high metal content Ir/Pt/Super P anode is one. The results suggest that increasing relative metal coverage is a practical approach to improve reversal tolerance and provide new insights into the reversal tolerant anodes design.

A new data-driven probabilistic fatigue life prediction framework informed by experiments and multiscale simulation

Traditional probabilistic fatigue life test requires long time, a large number of samples and high cost due to dispersion, randomness and complexity. A new data-driven probabilistic fatigue life prediction framework informed by experiments and multiscale simulation, was proposed and applied to a Ni-based superalloy FGH96. It exhibits the advantages of less tests and fully consideration of the effects of microstructure dispersion on fatigue crack initiation, small fatigue crack (SFC) and long fatigue crack (LFC) propagation. The fatigue crack initiation life was accurately predicted by a stored energy model of persistent slip band (PSB) based on microscale crystal plasticity (CP) theory. The usage of artificial neural network (ANN) leads to the capability of rapidly obtaining CP parameters through the macroscopic Ramberg-Osgood (RO) relationship. Bayesian neural networks (BNN) was trained to predict probabilistic fatigue crack initiation life, SFC and LFC growth rates based on results obtained from CP modellings and carefully designed experiments. With BNN as a probabilistic distribution generator, a Monte Carlo (MCs) model is developed to capture the complete fatigue failure processes, including the crack initiation, SFC and LFC propagation. The total fatigue life and the proportions of life at different stages of superalloy FGH96 were predicted by MCs, which agree well with the experimental data. This work provides a new pathway for structural safety assessment and damage tolerance design.

An improved method of parameter and tolerance concurrent design considering the mass loss

Quality and cost are the core problems in the manufacturing industry. Given the problems of many tests and high manufacturing costs caused by parameter design before tolerance design in the traditional Taguchi product optimization design, based on the idea of robust design and concurrent design, this paper establishes an improved method of parameter and tolerance concurrent design considering quality loss, which effectively saves the manufacturing cost while ensuring the product quality. Firstly, the central composite bounded experimental design (CCI) is carried out, and then the response surface model is established from the data; Then the total cost model composed of the quality loss model and tolerance cost model is established. Finally, the improved genetic algorithm (NSGA - II) is used to find the optimal parameter combination and tolerance at the same time. Through the example analysis of a compliant precision positioning platform, the results show that the parameter combination and tolerance obtained by concurrent design considering the parameters and tolerance of mass loss not only improve the robustness of products but also reduce the manufacturing cost.

A cyclic plastic zone size-based defect tolerant design approach to predict the fatigue life of additively manufactured alloys

The primary obstacles to utilizing additively manufactured metallic alloys in industry are their inadequate ductility and manufacturing imperfections. Defects in the alloys can result in stress concentration, which can further deteriorate their tensile ductility and fatigue performance. In this study, defect tolerant design methods based on physics are explored to forecast the fatigue performance of 17-4 PH stainless steel that has been additively manufactured. A cyclic plastic zone size-based finite element approach is proposed in this work to predict the fatigue performance of additively manufactured alloys. Initially, defects will be identified from the microstructure of the material, and a finite element model will be created from the microstructure; then, a kinematic hardening model will be used to determine the size of cyclic plastic zone around all defects. The largest size of cyclic plastic zone will cause failure and be identified as a killer defect, and the fatigue life will be calculated on the basis of that killer defect. The proposed method predicts the fatigue life of additively manufactured alloys well.

A study of tolerance allocation and stack-up analysis to improve the assembly precision of an injection mold

ABSTRACT Tolerance designing is a critical job for the assemblies to ensure their precision and functions. Tolerance design must consider manufacturing capability for ensuring the feasibility of the designs in the following processing. This paper presents the available methods of determining tolerance sizes and tolerance analysis to improve assembly precision. An injection mold consisting of hundreds of parts is used as an example to depict the methods of tolerance designing. The precision grades and the corresponding tolerance ranges applied in engineering fits are introduced for giving reasonable tolerances in designing. The defect rates of the designed tolerances to the machining precisions are investigated for observing the effects of manufacturing capabilities. An approach based on block assembly is proposed for eliminating tolerance stack-up, as well as improving assembly precision. The assembly tolerances can be reduced from 0.071 to 0.032 mm by using the proposed method, and the defect rates in manufacturing can be improved from 9.05% to 0.02%. It means that a larger range of tolerances can be designed to meet the specifications, as well as reduce the manufacturing costs.

Optimization of 3D Tolerance Design Based on Cost–Quality–Sensitivity Analysis to the Deviation Domain

Under the new geometric product specification (GPS), a two-dimensional chain cannot completely guarantee quality of the product. To optimize the allocation of three-dimensional tolerances in the conceptual design stage, the geometric variations of the tolerance zone to the deviation domain will be mapped in this paper. The deviation-processing cost, deviation-quality loss cost, and deviation-sensitivity cost function relationships combined with the tolerance zone described by the small displacement torsor theory are discussed. Then, synchronous constraint of the function structure and tolerance is realized. Finally, an improved bat algorithm is used to solve the established three-dimensional tolerance mathematical model. A case study in the optimization of three-part tolerance design is used to illustrate the proposed model and algorithms. The performance and advantage of the proposed method are discussed in the end.

Platform Tolerant RFID Tag Antenna Design for Safety and Real-Time Tracking of On-site Workers at Riskier Workplaces

The safety of workers is significant when talking about large risky workplaces such as construction job sites. Therefore, we proposed a UHF-RFID tag antenna that can be used to identify various Job site equipments and also construction workers by tagging their wearable helmets. Here, the compact, low profile, and simple structured platform-tolerant RFID tag antenna is proposed and optimized for metal sheet and ABS-based safety helmets. Furthermore, WTMiddleware (Worker Tracking Middleware) using Javascript, CSS, and HTML has been implemented to demonstrate a real-time secured web-based remote access of workers to provide their actual on-site monitoring and tracking of construction equipment carried/operated by the workers for tracking solutions. First, the fabricated tag’s performance was tested successfully in an outdoor scenario on various mountable materials such as wood, glass, plastic, and metal. The tag yielded a reasonable read range of 5.9 m on metallic sheet and 7.1 m on plastic with the highest read distance of 9.3 m on a glass sheet. Also, the measurement setup along with developed WTMiddleware was deployed in an actual workplace to demonstrate practical utility of the designed tag affixed on workers’ safety helmets. It was observed that all the workers wearing tagged helmets were successfully identified, tracked, and monitored. Also, their real-time on-site details, working zone, and complete personal details were accessed through a developed web page application via WTMiddleware.

Design of Fault Tolerant Array Multiplier Using Parity Preserving Reversible Gate

The digital designs with Reversible logic are more popular now days because of the increased demand of low power usage. Some of the Reversible logic gates are discussed in this paper. This paper also introduces a Parity Preserving Reversible Gate (PPRG) which is used in the fault tolerant devices design such as adders, subtractors and multipliers. The design of an array multiplier by using fault tolerant parallel adders is discussed in this paper. The fault tolerant parallel adders are designed using fault tolerant full adders and half adders and these adders are designed through Parity Preserving Reversible Gate. These adders and multipliers are useful in designing complex circuits such as ALU.

Rotor Fault Detection and Identification in Multirotors Based on Supervised Learning

This work presents the development of a fault detection and identification module for multirotor unmanned aerial vehicles (UAVs), capable of detecting a total failure in any of its rotors. The solution is based on a supervised learning approach, for which random forest and support vector machine classifiers have been trained using simulated data, and proved to be feasible to implement in real time. To validate these models, experimental proof will be shown of a classifier running in real time onboard a particular fault tolerant hexarotor design, showing the fastest detection times in this vehicle to date.

Discovery of quasi-disordered truss metamaterials inspired by natural cellular materials

Natural cellular materials, such as marine mussels, honeycombs, woods, trabecular bones, plant parenchyma, sponges and protoreaster nodosus, may benefit from the disorderliness within their internal microstructures to achieve damage tolerant behaviors. Inspired by this, we have created quasi-disordered truss metamaterials (QTMs) via introducing spatial coordinate perturbations or strut thickness variations to the perfect, periodic truss lattices. Numerical studies have suggested that the QTMs can exhibit either ductile, damage tolerant behaviors or sudden, catastrophic failure mode, depending on the distribution of the introduced disorderliness. A data-driven approach has been developed, combining deep-learning and global optimization algorithms, to tune the distribution of the disorderliness to achieve the damage tolerant QTM designs. A case study on the QTMs created from a periodic Face Centered Cubic (FCC) lattice has demonstrated that the optimized QTMs can achieve up to 100% increase in ductility at the expense of less than 5% stiffness and 8%–15% tensile strength. Our results suggest a novel design pathway for architected materials to improve damage tolerance.

Fatigue behaviour of plain and reinforced concrete: A systematic review

Damage tolerance design approach such as the fatigue crack propagation approach provides a more realistic solution for fatigue problems in concrete to overcome the limitations associated with the conventional design approach. The fatigue response of concrete is characterised by different fracture parameters, which have substantial impact on structural integrity and serviceability. Till now, many researchers have studied the fracture behaviour of concrete under static as well as fatigue loading. A critical review considering aspects which affects the fatigue fracture behaviour of concrete is necessary to represent the available information in a more systematic format. The goal of comprehensive assessment of the fracture behaviour of concrete is to understand the mechanics behind the different mechanisms of failure under fatigue loading. Real-time damage of structures must be quantified in order to create robust damage quantification models using various concepts. This will be helpful to recommend improved design and rehabilitation schemes to reduce structural failure. In this review, firstly a brief introduction is given describing the necessity of fatigue and fracture analysis in concrete. The studies on existence of Fracture Process Zone and estimation of its shape and size have been highlighted. A detailed study of size effect is then presented which mentions the different types of size effect laws that evolved with time. The evolution of crack growth rate laws in concrete is discussed in a detailed manner. Furthermore, a rigorous study has been done on various fatigue crack growth characterising factors such as loading rate, reinforcement ratio, coupled corrosion fatigue, bond slip, and temperature. Finally, the review is concluded with the studies on artificial neural networks, machine learning, and deep learning in the domain of fatigue and fracture analysis of concrete. Based on this review, various research gaps and open problems are identified for future reference.

Numerical shape, thickness and stacking sequence optimisation and experimental study of hybrid composite plates under in-plane shear loading

Shape, thickness and stacking sequence optimisation of a damage tolerant hybrid (GFRP-CFRP) composite laminate is performed using the commercial Optistruct solver. The results of the optimisation study are compared to both a benchmark non-damage tolerant CFRP laminate (without protective surface GFRP plies known as type 1 laminate) and a damage tolerant traditionally optimised hybrid CFRP-GFRP laminate (having X shape CFRP plies known as type 2 laminate), designed and tested in a previous study. The optimised laminate is manufactured using three different manufacturing techniques. The experimental buckling and post-buckling performance of the manufactured laminates are investigated. The optimised hybrid laminate is approximately 8% heavier than the type 1 but 17% lighter than type 2, but with the benefit of protective surface GFRP plies in favour of a damage tolerant design as shown in a previous study. Both numerical and experimental buckling and post-buckling performance studies show that the optimised laminates demonstrate higher pre-buckling stiffness compared to the type 1 design. However, the experimental buckling and failure/collapse loads, unlike the numerically predicted loads, are 24.31% and 26.70% lower, respectively. This is due to the significant number of ply drop-offs in the hybrid laminate design, and hence geometric imperfections and stress concentration effects at these locations leading to early buckling and failure in the post-buckling region.