Static Failure Research Articles

Experimental investigations of static mechanical properties and failure characteristics of damaged diorite after dynamic triaxial compression

To investigate the static mechanical properties and failure characteristics of damaged rocks after impact under realistic in-situ stress, dynamic triaxial compression tests with different strain rates and confining pressures were conducted on diorite by a modified split Hopkinson pressure bar . The damage factor was calculated according to the change of the longitudinal wave velocity of rocks before and after the impact, and the residual strengths of the damaged diorite were obtained by uniaxial compression and Brazilian tensile tests . In addition, three brittleness indexes based on the residual strength were adopted to evaluate the brittleness of damaged specimens, and fractal dimension was introduced to study the fragmentation characteristics. The results show that the dynamic peak stress, strain, elastic modulus , damage factor and plastic deformation of diorite all increase with increasing strain rate, i.e., rate dependence, and the increasing rate decreases with increasing confining pressure. The increment in confining pressure leads to the increase of dynamic peak stress, elastic modulus, static residual strength and brittleness, and the increasing rate increases with increasing strain rate, while other physio-mechanical parameters decrease with confining pressure. The post-peak behavior of dynamic stress-strain curves is divided into two classes according to the strain rate and fracture state of rocks under dynamic loading. Upon the strain rate increases above 87 s −1 , the brittleness of damaged specimens generally decreases to moderately brittle or even low brittle, and the corresponding drillability becomes much easier. The fractal dimension of damaged specimens increases with the increase of confining pressure and decreases linearly with the increase of strain rate .

Optimal face sheet thickness of 3D printed polymeric hexagonal and re-entrant honeycomb sandwich beams subjected to three-point bending

This study sheds light on designing optimized 3D printed polymeric sandwich beams by utilizing the practical aspect of the failure mechanisms. Obtaining an optimal face sheet thickness based on the static failure mod map is the main aim of this work. In order to achieve this purpose, the performance of 3D printed hexagonal honeycomb and re-entrant honeycomb sandwich beams, which were fabricated by the fused deposition modeling (FDM) technique, with four specific face sheet thicknesses under three-point bending were assessed. The mechanical behaviors were evaluated using the extended finite element method (XFEM) in ABAQUS software, and the digital image correlation (DIC) analyses were employed to display the cracks that are not visible to the human eye. The numerical results with less than 6.6% error were confirmed with experimental ones. The current meticulous investigation discloses that the static failure map of a 3D printed polymeric sandwich beam with multi-row cellular lattice core is divided into face fracture and core shear modes, which has not been reported yet. The tremendous achievements provide novel insight into determining an optimal face sheet thickness and its relation with the growth rate of energy absorption capacity. Experimental investigation reveals that increasing face sheet thickness by one millimetre from H 2 to H 3 and R 2 to R 3 enhances energy absorption capacity by about 11% and 19.8%, respectively.

Joining Properties of SPFC440/AA5052 Multi-Material Self-Piercing Riveting Joints.

With the development of new energy vehicles, the joining of lightweight alloys has received more attention. Self-piercing riveting experiments of aluminum alloy and high-strength steel sheets were performed to analyze the effects of rivet height and laying order of metal sheets on the joining quality in the work. The forming surface, cross-sectional morphology, static tensile property, fatigue property, failure mode, and mechanism were analyzed. The results show that AA5052 alloy and SPFC440 steel can be joined effectively by self-piercing riveting, and there is good contact between rivet head and sheet surfaces. When the rivet is 2.5–3.5 mm higher than the total thickness of two layers sheets, the rivet leg flares symmetrically without cracks or buckling, and the lower sheet completely encapsulates the joint button. The joints have better static tensile properties when the rivet is about 3 mm higher than the thickness of two sheets. The higher static strength is obtained when the aluminum alloy is placed at the lower position. The rivet legs fall off from the lower sheets for all the samples in the tensile tests, which is independent of the rivet height and laying order of metal sheets. The fatigue strength of the sample with the rivet height of 7 mm is the greatest, and the fatigue cracks always occur on the aluminum sheet under all experimental conditions. The findings in this work can help the practical application of self-piercing riveting for aluminum/steel sheets.

The State of Pore Fluid Pressure and 3‐D Megathrust Earthquake Dynamics

AbstractWe study the effects of pore fluid pressure (Pf) on the pre‐earthquake, near‐fault stress state, and 3‐D earthquake rupture dynamics through six scenarios utilizing a structural model based on the 2004 Mw 9.1 Sumatra‐Andaman earthquake. As pre‐earthquake Pf magnitude increases, effective normal stress and fault shear strength decrease. As a result, magnitude, slip, peak slip rate, stress drop, and rupture velocity of the scenario earthquakes decrease. Comparison of results with observations of the 2004 earthquake support that pre‐earthquake Pf averages near 97% of lithostatic pressure, leading to pre‐earthquake average shear and effective normal tractions of 4–5 and 22 MPa. The megathrust in these scenarios is weak, in terms of low mean shear traction at static failure and low dynamic friction coefficient during rupture. Apparent co‐seismic principal stress rotations and absolute post‐seismic stresses in these scenarios are consistent with the variety of observed aftershock focal mechanisms. In all scenarios, the mean apparent stress rotations are larger above than below the megathrust. Scenarios with larger Pf magnitudes exhibit lower mean apparent principal stress rotations. We further evaluate pre‐earthquake Pf depth distribution. If Pf follows a sublithostatic gradient, pre‐earthquake effective normal stress increases with depth. If Pf follows the lithostatic gradient exactly, then this normal stress is constant, shifting peak slip and peak slip rate updip. This renders constraints on near‐trench strength and constitutive behavior crucial for mitigating hazard. These scenarios provide opportunity for future calibration with site‐specific measurements to constrain dynamically plausible megathrust strength and Pf gradients.

Reliability analysis of composite sandwich structure for fuselage skin based on surrogate model

Composite structures are characterized by multiple source uncertainties in mechanical properties, geometric dimension, etc., and multiple failure modes, which bring challenges to their design and application. In order to explore the reliability analysis method of composite sandwich structures with multi-source uncertainties and multi-failure modes, a parametric finite element model and an acoustic boundary element model were established for deterministic analysis of a fuselage skin sandwich structure. Considering the randomness of the mechanical properties of composite materials and the laminate thickness, the structural reliability models were established for three typical failure modes of sandwich structures: static strength failure, global buckling and vibration noise. In order to reduce the computational effort, the Kriging surrogate models of failure modes were constructed, and the subset simulation method was used to predict the system failure probability of the sandwich structure of fuselage skin. The proposed computational framework provides support and tool for the fine design of composite sandwich structure.

Fatigue and static damage in curved woven fabric carbon fiber reinforced polymer laminates

Failure mechanisms of curved cross-ply laminates under static and fatigue loading have been studied extensively, but the examination of fabric laminates which are the most commonly used ply type in curved supports in airplane wing structures is lacking. In this study, unidirectional (UD) and fabric carbon fiber reinforced polymer (CFRP) laminates are examined to elucidate the failure initiation mechanisms of laminated composites under fatigue and static loading. The crucial point of the research is applying the analyses using fabric laminate with a currently used stacking sequence in commercial airplanes. In addition to the fabric laminate, UD laminate is also included in the research to compare the real complex stacking with the simplest stacking. In the experiments, it is observed that both static and fatigue failures initiate roughly at the maximum radial stress location (approximately 35% of the thickness from the inner radius). For UD laminates, there is no visible difference between the failure mechanisms under static and fatigue loadings. However, for fabric laminates, fatigue failure is observed to occur as a single major crack at the maximum radial stress location as in UD laminates, whereas static failure is observed to occur as multiple diffusive cracks at the maximum radial stress location. Additionally, cracks grow mostly as intralaminar cracks connected with regions of occasional interlaminar cracks.

Failure Analysis of Hat-Stringer-Stiffened Aircraft Composite Panels under Four-Point Bending Loading.

Hat-stringer-stiffened composite panels have been widely used in aircrafts. Accurate failure analysis of them is important for the safety and integrity of the fuselage. During the service period, these panels will bear not only the lateral force caused by the bending of fuselage, but also the radial pressure caused by the internal and external differential pressure during the take-off and landing of the aircraft. However, the latter case lacks investigation. Therefore, experimental and numerical studies for the static and fatigue failure of hat-stringer-stiffened composite panels under four-point bending loading have been performed in this work. To accurately predict the fatigue failure, a novel theoretical model has been proposed based on the fatigue damage theory. In addition, a user-defined subroutine USDFLD is developed for the implementation of the proposed theoretical model in Abaqus. Experimental results show that the main failure modes are the delamination of the skin and debonding between the girder flange and the skin. The experimental average value of the initial debonding load and displacement in static tests are 897.3 N and 10.8 mm, respectively. Predictions exhibit good agreement with experimental results with relative errors within 10%. Experimental average fatigue failure life of the specimens is 33,085 cycles, which is also close to the prediction with relative errors within 10%. This indicates the reliability and applicability of the established theoretical model and numerical method for predicting the failure of hat-shaped girder structures.

A failure tracing method with hierarchical digraph and meta action for complex electromechanical systems

AbstractAs an important method for analyzing the failure pervasion mechanism, failure tracing is a powerful tool for locating the failure causes in reliability analysis of complex electromechanical systems (EMS). However, most of the previous studies mainly focus on the failure tracing and identifying of part levels, which are often complicated. Besides, they cannot reflect the product feature that motion determines product function. To fill these gaps, this paper develops a combined dynamic and static failure tracing model based on meta action and hierarchy digraph model. First, the failure propagation directed digraph is constructed based on the structure of the EMS and the interactions of action signals, and the interpretative structural model (ISM) is further applied to obtain the hierarchy failure propagation model based on the directed digraph. Second, the combined dynamic and static failure propagation intensity between meta actions is measured based on the failure propagation probability and edge betweenness, which can effectively extract the crucial pathway and crucial meta actions to facilitate failure tracing. Third, a failure mode and effect analysis (FMEA) method considering the weights of risk elements and experts is proposed to estimate the risks of the crucial meta actions’ failure modes, which can help engineers develop countermeasures for preventing or eliminating failures. Finally, a case study and several comparisons are presented to illustrate the feasibility and benefits of the developed model.

HV-LDMOS Device Engineering Insights for Moving Current Filament to Enhance ESD Robustness

In this article, a novel design approach for improving electrostatic discharge (ESD) robustness of high-voltage laterally double-diffused MOS (LDMOS) devices is presented using detailed 3-D TCAD simulations. The proposed method considers engineering both static filament and dynamic/moving current filaments in LDMOS design. Physical insights and engineering approaches for moving filaments at higher stress current levels are presented. Dynamic filament motion and its relation to n-p-n turn-on engineering with an optimum p-well profile and substrate biasing are revealed. A unique window failure in LDMOS near snapback is discussed for the first time. A detailed analysis is presented on filament width engineering by using optimum drain diffusion length (DL) and its influence on static filament-induced window failures. This approach resulted in ten-time improvement in ESD robustness for self-protecting concepts. Finally, different fundamental questions related to the origin of filament motion are explored (using 3-D TCAD) with the help of engineered LDMOS Designs.

Research on the failure mechanism of the high-speed train bearing steel under static load failure

Bearing plays an important role in operation safety as the key component of high-speed train. The service life is affected by the fracture behavior of bearing during operation seriously. In this paper, the MTS universal testing machine was used to carry out tensile test and tension-unloading test on the sample of the bearing outer ring. On this basis, the fracture process was dynamically monitored by in-situ tensile test. The stress state of the sample during tensile process was calculated by the finite element software ABAQUS. The results show that the microstructure is composed of lower bainite, (Fe,Cr)3C carbides and a small amount of residual austenite. The ultimate strength of outer ring is 2.3GPa. Compared with the center of the sample, the stress triaxiality on the surface is low and the shear stress is high relatively, reinforcing the local plastic deformation. Microcracks are the main damage forms of bearing outer ring. The microcracks nucleate in the three sites, which are the boundary of bainite colony, between the bainite lamellae and around carbide. The bainite colony is the weakest link of the bearing. A large number of microcracks nucleate on the boundary of bainite colony. Under the action of tensile loading, the microcracks propagate along the boundary of bainite colony. With the increasing of load, the cracks propagate unsteadily and lead to the quasi-cleavage fracture of the sample.

Impact behavior of superspeed granular flow: Insights from centrifuge modeling and DEM simulation

The impact behavior of superspeed granular flows is not sufficiently understood, although it is the basis for establishing an impact model, which is important in barrier design. Centrifuge-based modeling is a promising tool for reproducing the superspeed nature of a granular flow under a prototype stress condition. Therefore, this study established a novel centrifuge model to investigate the effect of flow speed and volume on the impact behavior of superspeed granular flows. To further verify our centrifuge modeling results and reveal more details of granular impact dynamics, a DEM-based numerical model operated under an actual centrifugal field and Coriolis field was used. The results reveal that the interparticle interaction consumed most of the granular flow energy in three ways: dead zone deformation, particle collision within the subsequent flow, and flow–dead-zone interaction, accounting for 8%, 82%, and 10%, respectively. The failure mode of the formed dead zone varied during the debris–barrier interaction, and a static failure mode is proposed to conservatively estimate the action force exerted by the dead zone. The total force on the barrier should include three main parts: the force caused by the self-weight of the dead zone, the force caused by the direct impact of granular flow after climbing on the ramp formed by the dead zone, and the force transmitted by the dead zone and generated by the interaction between the dead zone and the subsequent flow. The third part is also important because it may account for a considerable portion of the total force (the percentage may depend on the dynamic characteristics of granular flow), but is not sufficiently addressed in existing impact models. Additionally, we found that a scale model under the reduced stress condition may underestimate the impact force; therefore, centrifuge-based modeling with a passive Coriolis condition is encouraged for investigating the impact behavior of superspeed granular flows.

Application of flexible pin for planetary gear set of wind turbine gearbox

Wind turbines are eco-friendly energy sources that generate electricity from wind power. Among their various components, gearboxes constitute the most critical loss owing to their longest downtime. To guarantee their durability, a flexible pin was designed based on the original straddle-mounted pin for enhanced tooth load sharing and distribution in the planetary gear set (PGS) of a wind turbine gearbox (WTGB). The improved durability was evaluated by calculating the mesh load factor and face load factor for contact stress and comparing these values with those of the original straddle-mounted pin. The mesh load factor decreased from 1.37 to 1.08, whereas the maximum face load factor decreased slightly, moderating the overall safety factor variation. Furthermore, the structure of the proposed flexible pin model was analyzed and verified that no static failure or interference occurred. Additionally, microgeometry optimization was applied to improve the load distribution. Therefore, it was verified that a flexible pin applied to a single helical-geared PGS, thus far considered impossible, enhances the durability of WTGBs by improving the load sharing and distribution of a PGS. Consequently, the possibility of designing single helical-geared planetary gearboxes with flexible pins to take advantages of both helical gears and flexible pins was shown analytically.

A PD-FEM approach for fast solving static failure problems and its engineering application

A method of coupling of peridynamics (PD) and finite element method (FEM) for fast solving static failure problems is proposed. It is based on the force coupling method and adopts interface elements to couple the PD and FE subregions. By assembling the global matrix of the coupling model and using the adaptive dynamic relaxation (ADR) method to solve it, the static solution of elasticity and crack growth problems can be obtained quickly. By introducing short-range repulsive force and re-defining the coupling force, it is not only suitable for simulating tensile failure problems, but also suitable for compression failure problems. Through comparative analysis, the accuracy and effectiveness of this approach are verified. And then the method is successfully applied to simulate the excavation process of an underground cavern group, and the simulation of damage and failure process of engineering rock mass under complex tension–compression conditions has been realized. The stability characteristics of the surrounding rock are revealed by analyzing the damage and deformation evolution laws. It provides an effective numerical simulation method for predicting the excavation damage zone (EDZ) distribution characteristics and deformation law of the surrounding rock during the excavation of an underground cavern group. At the same time, compared with pure PD, the calculation efficiency is greatly improved, which is of great significance for the realization of engineering-scale simulation.

Effects of dynamic fibre failure in unidirectional composites

The stress redistribution around a broken fibre is a substantial issue in longitudinal strength analysis of unidirectional (UD) composites. Most investigated models are based on a regular fibre packings and classical shear lag theory (static failure) that considers pre-broken fibers, where the dynamic aspects of brittle fiber failure are not considered. In the present work, Representative Volume Elements with random fibre packings were modeled by means of 3D finite element analysis, and simulated considering the event of dynamic fibre failure. Significant effects were observed on the stress concentration factor (SCF) and ineffective load length which are related to the fibre debonding length and the volume of matrix damage-plasticity zones. Hence, it can be concluded that an accurate representation of the stress redistribution after a fibre breakage event requires consideration of dynamic effects.

Coseismic and postseismic deformation of the 2016 Mw 6.0 Petermann ranges earthquake from satellite radar observations

Continental earthquakes, especially shallow earthquakes, can cause disasters in populated areas. On 20 May 2016, a moderate magnitude earthquake (Mw 6.0) ruptured on Northern Territory of Australia. With the aim of seismic hazard assessment, coseismic and postsesmic deformation of the Petermann earthquake has been determined using ALOS-2 ascending and Sentinel-1A descending images. The coseismic deformation field suggests that the earthquake ruptured in the NNW direction with a length of about 20 km, a rake angle of 57.1° and a moment magnitude of Mw 6.06. The maximum slip of 1.31 m can be observed at the depth of 1.25 km. The small baseline subset (SBAS) InSAR was utilized to obtain the postseismic deformation from 69 Sentinel-1A images in a descending orbit. The spatiotemporal evolution of the postseismic deformation presents a gradually decaying trend, with a maximum displacement of 5.4 cm within 858 days after the mainshock. Our afterslip model suggests that the maximum slip of 0.28 m occurred at the depth of 0.25 km with a slight shift to the northwest compared to the coseismic slip. The static Coulomb failure stress (CFS) changes at various depths were calculated, indicating the consistency between high loaded stress zones and aftershock distribution.

ВЛИЯНИЕ КРУПНОГО ЗАПОЛНИТЕЛЯ НА ЭНЕРГЕТИЧЕСКИЕ И СИЛОВЫЕ ХАРАКТЕРИСТИКИ СТАЛЕФИБРОБЕТОНА

At present, composite materials are gaining more and more development in construction, including the use of dispersed reinforced concrete, which is due to its significantly improved physical, mechanical and operational characteristics compared to traditional concrete and reinforced concrete. The article presents the results of the influence of coarse filler in the composition of the composite on the energy and power characteristics of the crack resistance of fiber-reinforced concrete reinforced with steel anchor fibers. The process of deformation and the mechanism of destruction of steel fiber reinforced concrete have been studied. To do this, in accordance with the provisions of GOST 29167 "Methods for determining the characteristics of crack resistance (fracture toughness) under static loading", steel-fiber-reinforced concrete sample beams were tested with control of the applied load and the deflection caused by it. Based on the data obtained, diagrams of the dependence of the load on the deflection were constructed, after their processing and additional constructions, the energy costs for static destruction, tensile strength in bending, and the stress intensity factor were determined. It has been established that the value of the conditional specific effective energy consumption for static failure and tensile strength in bending of fiber-reinforced concrete samples with a matrix of heavy concrete with coarse aggregate turned out to be lower than that of fiber-reinforced concrete samples with a matrix of fine-grained concrete, which is explained by the lower adhesion of the steel anchor fiber to the matrix, and a corresponding decrease in their efficiency.

Design and development of all wheel drive transmission system for an all-terrain vehicle

An All-Wheel Drive Transmission system powered by a 10 HP Briggs & Stratton engine is designed for a single-seater all-terrain vehicle. Because of the engine power limitation, it's important to reduce the vehicle's weight and improve its performance. The aim is to increase the traction of the vehicle and it must be able to climb high grades, cross slippery mud pools, and snow tracks with minimum drive slip. While performing, the system must be reliable and not fail under any circumstances. The study focuses on the optimized calculation of engine performance, vehicle mass, air drag, rolling resistance, continuously variable transmission (CVT) shifting, gearbox reduction ratio, gear selection, shaft, and casing. The design and analysis process includes the development of a compound gear train with gears having a minimum diameter and face width, to lower the rotational inertia of the system and included the calculation of static failure from contact and bending stresses, gearbox housing, shafts, and bearings. All components are designed in Solidworks 2016 and analyzed in Ansys Workbench 19.2.

Corrosion effects on structural integrity and life of oil rig drill pipes

Corrosion effects on structural integrity and life of oil rig welded pipes are analysed by experimental, analytical, and numerical methods. Experiments were performed using standard tensile specimens and CT specimens for static loading, Charpy specimens for impact loading, and 3 Point Bending specimens for fatigue crack growth with amplitude loading. In each case new and old pipes were used to evaluate corrosion effects. Results indicated negligible corrosion effects in the case of tensile properties and impact toughness, and strong effects in the case of fracture toughness and especially fatigue crack growth rates, increasing the risk of static failure and reducing significantly structural life. Analytical expressions are used for oil rig pipe structural integrity and life assessment to quantify these effects. Recently introduced risk-based approach is applied to analyse oil rig drill pipe with a corrosion defect treated as a surface crack.

Investigating on the influence of multi‐walled carbon nanotube and graphene nanoplatelet additives on residual strength of bonded joints subjected to partial fatigue loading

AbstractAdhesively bonded joints in engineering structures, especially automotive body structures, inevitably experience long or limited fatigue loading conditions. In this article, the shear strength of steel bonded lap joints reinforced by multi‐walled carbon nanotube (MWCNT) and graphene nanoplatelet (GNP) were evaluated after being subjected to limited fatigue loading cycles. For this purpose, three specimen groups of neat, MWCNT, and GNP‐reinforced joints (with 0.2, 0.5, 1.0, and 2.0 wt% contents) were prepared. After performing the static lap shear tests, fatigue testing of each specimen group was conducted under a maximum fatigue load of 50% of its average static failure load until complete separation of the substrates. Accordingly, limited fatigue loadings were applied to each specimen group for 30%, 50%, and 70% of its total fatigue life, and subsequently, a second‐round static testing was performed to evaluate the residual strength of the joints. The results revealed that the maximum static shear strength improvements of MWCNT and GNP‐reinforced joints were associated with incorporating 1.0 and 0.5 wt% particle contents. Moreover, for 0.2 and 0.5 wt% contents, the static strength of the joints reinforced by GNPs was 3.4% and 3.9% greater than that of MWCNTs reinforced joints. On the contrary, for 1.0 and 2.0 wt% filler contents, specimens including MWCNTs had 9.1% and 18.6% higher strength than GNP‐reinforced ones. The highest fatigue life enhancements of 34.1% and 31% were obtained by adding 1.0 and 0.5 wt.% of MWCNT and GNP particles to the adhesive, respectively. It was concluded that, for 0.2 and 0.5 wt% contents, nanoparticle type did not have a noticeable effect on the residual strength of the joints after being subjected to fatigue loading for 30% of its total life. The specimens subjected to 50% and 70% of their total fatigue life indicated a minimum loss in the shear strength for the joints reinforced by dispersing 1.0 wt% of MWCNTs.

Rear Fuselage Structural Optimization Using Genetic Algorithm

Structural optimization is one of the most important tasks during the airplane structural design and yet there is a lack of well established procedures to determine the optimum design of aerospace structures. This paper represents development of structural optimization code based on genetic algorithm, and results for light aircraft aft fuselage optimal design using the optimization code. We have developed a MATLAB code according to the genetic algorithm and FE model for the composite light aircraft aft fuselage using MSC PATRAN to generate NASTRAN input file; the MATLAB code was coupled with MSC NASTRAN which used to perform linear static and buckling analysis. we obtained the minimum weight of the aft fuselage with a linear static and buckling constraints; the minimum weight is 21.6 kg; it has been obtained after 43 iterations; the margin of safety is of the optimum design is 1.22 and the buckling factor is 1.24 and hence the structure is free of static failure and buckling. The code is efficient in the conceptual and preliminary structural design phases to obtain the optimal aft fuselage weight.