Severe Impact Loading Research Articles

Analysis of Scraper Conveyor Chain Dynamics under Falling Coal Impact Conditions

The scraper conveyor, essential for mechanized mining, operates in harsh underground environments and is subjected to severe impact loads from coal and rock falls. Such conditions can cause chain jamming, breakage, and other malfunctions, necessitating a detailed study of the system’s dynamic behavior under impact conditions. This study investigates the dynamic characteristics of a scraper conveyor’s chain drive system using a coupled ADAMS-EDEM simulation model. The model analyzes the effects of loaded coal piles on the conveyor’s dynamics during normal and impact conditions. Simulations show that loaded coal piles excite the scraper’s acceleration and sprocket rotation, with the greatest impact in the scraper’s running direction. Longitudinal impact and contact forces on the chain ring are more significant than in other directions under both no-load and loaded conditions. A strong linear relationship exists between the falling coal mass and longitudinal impact force. The coal pile causes prominent longitudinal vibration excitation while inhibiting the overall vibration of the chain drive system to some extent. The findings provide insights for identifying failure-prone areas under impact conditions and offer theoretical guidance for optimizing scraper conveyor design. This enhances mining efficiency and safety in coal operations.

Numerical Study on Modeling and Local Characteristics of a Predetermined Freak Wave

Abstract A numerical study on the modeling and local characteristics of a predetermined freak wave has been conducted with Computational Fluid Dynamics method. Following the available experimental investigations, a numerical wave tank was accordingly set up based on openfoam source packets. The experimental flap-type wave-maker motion was employed directly to reproduce a specific freak wave. The effects of mesh scheme on freak wave modeling were investigated in depth. Reasonable agreements were achieved between the numerical and experimental results. The wavelet transform method was applied to demonstrate the energy structures of freak wave trains. Special attentions were paid to the particle velocities as well as the dynamic pressure. The results showed that insufficient mesh resolutions could probably result in energy dissipations and phase errors of high-frequency wave components during wave propagations which in turn lead to the shifts of focal positions of freak waves. The particle velocities near the wave crest are extremely large, indicating possible severe wave breaking and impact loads. The theoretical values of similar-shape regular waves could considerably underestimate the particle velocities of freak waves.

Impact Resistance of CVD Multi-Coatings with Designed Layers

Coated cutting tools are widely used in the manufacturing industry due to their excellent properties of high heat resistance, high hardness, and low friction. However, the milling process is a dynamic process, so the coatings of milling tools suffer severe cyclic impact loads. Impact resistance is important for the life of milling tools. Multi-coatings with different layer thickness may influence their impact resistance, but few studies focus on this topic. In this study, CVD coating with a structure of TiN layer, Al2O3 layer, and TiCN layer was selected as the research objective. Four different CVD coatings with different layer thicknesses were designed and prepared. The impact resistance test method was proposed to simulate the impact due to cut-in during down the milling process. We obtained the load by setting an impact depth of 25/30/35 µm, recording the impact force during the impact process, and calculating the contact stress; it was found that, at the impact depth of 25/30/35 µm, the download loads were around 9/11/13 N, while the contact stresses were all around 1 GPa. The failure morphology of the coating surface was investigated after the impact process. By comparing the contact stress and the surface morphology of the designed coatings, the impact resistance of four kinds of designed CVD coatings were evaluated. Experiments have shown that an increase in coating thickness and total coating thickness reduces impact resistance by about 10%. The impact resistance of coating samples without a TiN surface layer also decreased by about 10%. When the surface layer of TiN was thinner than 1 µm, the surface layer of TiN was prone to chipping and peeling off. Decreasing the thickness of the middle layer of Al2O3 and increasing the thickness of the inner layer of TiCN obviously lowered the impact resistance.

Numerical analysis of sandwich panels under high-velocity impact

Composites are gaining importance in aircraft structures, due to their high specific strength, stiffness, and low weight. There are different types of composites used in aircraft structures out of which carbon fiber reinforced polymer (CFRP) serves best in the aircraft industry. Half of the weight of the Boeing 787 is made of CFRP and other composites that reduced the weight of the aircraft by 20% as compared to the conventional design with aluminum alloy. Similar to CFRP the recent trend focused on the usage of sandwich structures in aircraft design. Sandwich structure is a composite material made of the lightweight thick core placed between the thin face sheets made of CFRP or Glass fiber reinforced polymer. During service, aircraft panels are subjected to severe structural, aerodynamics loads, and impact loads. These loads cause severe damage to the structure that affects the residual strength. The impact is the more susceptible damage in composite panels. In this paper, a numerical impact analysis of the sandwich panel is carried out. There are different parameters that influence the impact strength of sandwich panels are face sheet material, core material, and thickness of the core. In this paper, finite element-based parametric analysis is carried out by varying face sheet materials such as CFRP, GFRP, Al alloy, Ti alloy, and core materials (such as honeycomb structure and PVC foam). Further, in this work, the combined MADM method using TOPSIS and AHP is applied to find out the optimal face sheet material for the sandwich panel. The attribute data for applying the MADM method is obtained from finite element analysis (FEA).

Probability of instant rail break induced by wheel–rail impact loading using field test data

ABSTRACT The probability of an instant rail break, initiated at a single pre-existing rail foot crack due to a severe wheel impact loading, is predicted using statistical methods and a time-domain model for the simulation of dynamic vehicle–track interaction. A linear elastic fracture mechanics approach is employed to calculate the stress intensity at the crack in a continuously welded rail subjected to combined bending and temperature loading. Based on long-term field measurements in a wayside wheel load detector, a three-parameter probability distribution of the dynamic wheel load is determined. For a faster numerical assessment of the probability of failure, a thin plate spline regression is implemented to develop a meta-model of the performance function quantifying the stress intensity at the crack. The methodology is demonstrated by investigating the influence of initial crack length, fracture toughness and rail temperature difference on the risk for an instant rail break.

An experimental and numerical study of reinforced conventional concrete and ultra-high performance concrete columns under lateral impact loads

This paper presents an experimental and numerical study on the dynamic behaviour of axially-loaded reinforced conventional concrete (RC) and ultra-high performance concrete (UHPC) columns against low-velocity impact loading. The test specimens were divided into two groups with square and circular cross-section shapes, and each group includes both RC and UHPC columns. The impact scenario was modelled with a drop weight falling freely on the column mid-span. Brittle failure with shear plug formation was observed in RC columns while UHPC columns remained a flexure response with minimal damage under severe impact loads. To further interpret the experimental data, detailed finite element (FE) models were developed for RC and UHPC columns. A Continuous Surface Cap Model (CSCM) which accounts for the triaxial material strength, post peak softening and strain rate effect was adopted for UHPC material. After validating the material and structural model based on the testing data, extensive numerical simulations were performed to predict the UHPC column residual loading capacity after lateral impacts. Impact mass-velocity (M-V) diagrams were derived for the UHPC column damage assessment, and analytical formulae which could be easily applied to generate M-V diagrams were derived based on parametric studies.

Gradient microstructure and enhanced mechanical performance of magnesium alloy by severe impact loading

Subjecting a workpiece to a surface treatment with severe impact loading is a novel severe plastic deformation procedure to fabricate gradient microstructures through the thickness and longitudinal direction. Mechanical performance is a function of twin density and the newly-formed grain size gradients. {101¯2} tensile twins created from processing without excessive grain refinement lead to strength enhancement with retained ductility. Creation of residual strain by a single impact results in a significant reduction in time and cost of the process. This paper investigates the effect of applying severe impact loading on mechanical and microstructural properties of magnesium for various impact velocities.

Impact failure analysis of corrugated steel plate in LNG containment cargo system

In the present study, the failure characteristics of the primary barrier of a GTT Mark-III type liquefied natural gas (LNG) cargo containment system (CCS) under cyclic impact loads were analyzed using a comprehensive failure model. The three types of failure modes that mainly occur in a thin-walled structure, namely, localized necking, ductile failure, and shear failure, were considered to evaluate the different failure phenomena for large and small corrugations of the primary barrier consisting of 304 L stainless steel. To validate the numerical analysis approach, a series of impact tests were conducted, and the reaction force history along with the permanently deformed configuration of the thin-walled structure was compared to the simulation results of structural impact failure. Through the comparative study, it was confirmed that the simulation outcomes were in good agreement with the experimental results. The proposed failure analysis model was used to quantitatively predict the structural impact failure of the primary barrier under severe impact (or sloshing) loads, and the estimated structural life was proposed based on the failure index concept.

Shock absorbing ability in healthy and damaged cartilage-bone under high-rate compression

Articular cartilage is a soft tissue that distributes the loads in joints and transfers the compressive load to the underlying bone. At high rate and magnitudes of mechanical loading, cartilage and subchondral bone together are susceptible to damage. In addition, any disruption to the cartilage's structure, caused by injury, trauma or disorder such as osteoarthritis (OA), can alter the mechanism of load transfer from the cartilage to the underlying bone. Changes in the cartilage structure can also alter the ability of cartilage-bone to absorb and dissipate the impact energy. To investigate the effects of cartilage degradation on cartilage-bone shock absorption ability, the top 50% of the cartilage thickness was removed (modified cartilage) to mimic the cartilage thickness reduction in Grade III cartilage lesion and the remaining cartilage-bone unit (modified cartilage-bone) was compressed at high-rate (4% strain at 5 Hz). High-speed camera and microscope were used to capture microscopic deformation, and digital image correlation technique (DIC) employed to quantify the deformation of cartilage and bone. The mechanical properties (i.e. stiffness, strain, absorbed and dissipated energies) of cartilage and bone were calculated before and after the removal of the top 50% of the cartilage thickness, consisting of both the superficial tangential zone (STZ) and part of the middle zone of the cartilage. The results showed a significant degradation in the mechanical properties of the cartilage-bone unit after the removal of the top 50% cartilage thickness. The stiffness of the modified cartilage reduced significantly (by ~39%) and energy absorption in underlying bone increased by 32%, which can make the bone more vulnerable to damage in the modified cartilage-bone unit. In addition, the energy dissipation in the modified cartilage-bone unit was also increased by approximately 14%. These changes in mechanical properties suggest a crucial role of the STZ and middle zone (within the top 50% cartilage thickness) in protecting the underlying bone from the severe compressive impact loading. Results also indicated that under physiological contact stress of 7 MPa, strain in damaged cartilage was increased by 3.22% without affecting the mechanical behaviour of the underlying bone.

The development and ballistic performance of protective steel-concrete composite barriers against hypervelocity impacts by explosively formed projectiles

Explosively formed projectiles (EFP) are one of the most severe explosive and impact loading threats for civil infrastructure and military vehicles. Currently, there is no effective means of protection for military vehicles and infrastructure facilities from EFPs. This paper presents the experimental results of the hypervelocity impact of EFPs on steel-concrete (SC) barrier systems of finite dimensions. The SC barrier units tested were broadly representative of the type of protective SC units used in the expedient construction of barriers for mitigating improvised explosive device (IED) and EFP threats to critical infrastructure facilities. The response of non-composite, partially-composite, and fully-composite SC barrier units was studied. All studied protective systems were capable of terminating the high-velocity projectiles effectively through the combined action of the concrete core and steel faceplates. The data gathered from these tests are also intended to further the understanding of impacts on SC composite structures at speeds greater than 1000 m/s and for the calibration of numerical models of EFP interaction with SC targets. 3D numerical simulations were performed to better understand the various stages of EFP interaction with the SC composite barriers and develop recommendations for their design optimisation. No previously published results on the EFP terminal ballistic performance of SC composite structures of finite dimensions have been found in the open literature.

3D transient elasto-plastic finite element analysis of a flatted railway wheel in rolling contact

ABSTRACTA precise study of stress state is crucial for an accurate evaluation of railway wheel defects. Wheel flats cause severe impact loads, which aggravate wheel failure. This paper describes 3D transient elasto-plastic finite element analyses of undamaged and flatted railway wheels using Chaboche’s plasticity model as material model. The effect of the impact load is considered on contact region parameters that influence the stress. The results show that in a flatted wheel, the maximum contact force might not lead to a maximum von-Mises stress. It occurs in all cases considered, in a cross-section just above the leading edge of the wheel flat.

Reply to Giannakos, K. Comment on: Toughness of Railroad Concrete Crossties with Holes and Web Openings. Infrastructures 2017, 2, 3

This paper responds to the discussion [1] by Dr. K. Giannakos over our technical note [2].[...]

MEMS Packaging Reliability in Board-Level Drop Tests Under Severe Shock and Impact Loading Conditions–Part I: Experiment

The continuing increase of functionality, miniaturization, and affordability of handheld electronic devices has resulted in a decrease in the size and weight of the products. As a result, printed wiring assemblies (PWAs) have become thinner and more flexible, and clearances with surrounding structures have decreased. Therefore, new design rules are needed to minimize and survive possible secondary impacts between PWAs and surrounding structures because of the consequential amplification in acceleration and contact stress. This paper is the first of a two-part series and focuses on the drop test reliability of commercial off-the-shelf microelectromechanical systems (MEMS) components that are mounted on printed wiring boards (PWBs). Particularly in this paper, we are interested in gaining preliminary insights into the effects of secondary impacts (between internal structures) on failure sites in the MEMS assemblies. Drop tests are conducted under highly accelerated conditions of 20 000 ${g}$ (“ ${g}$ ” is the gravitational acceleration). Under such high accelerations, the stress levels generated are well beyond those expected in conventional qualification tests. Furthermore, secondary impacts of varying intensities were allowed by changing the clearance between the PWB and the fixture. As a result, the stress and accelerations are further amplified, to mimic unexpected secondary impacts in a product if/when design rules fail to avoid such conditions. The amplification of the test severity is quantified by comparing the characteristic life ( $\eta $ in a Weibull distribution) of all the tested MEMS components at each clearance. Multiple failure sites from drop testing are identified, from packaging-level failures to MEMS device failures. The participation of competing failure sites is also demonstrated via characteristic life representations of each failure site at various clearances.

MEMS Packaging Reliability in Board-Level Drop Tests Under Severe Shock and Impact Loading Conditions—Part II: Fatigue Damage Modeling

Damage in handheld electronic devices due to accidental drops is a critical reliability concern. This paper is the second of a two-part series and focuses on damage models for drop test durability of commercial off-the-shelf microelectromechanical systems (MEMS) components that are mounted on printed wiring boards. The modeling approach is based on the experimental results presented in the first part of this two-part series. In particular, the focus of this paper is on damage due to drop events under extremely high accelerations (20 $000g$ , where $g$ is the gravitational acceleration) achieved by a series of secondary impacts. Impacts with such high accelerations can occur in handheld electronic devices due to collisions between internal neighboring structures and can generate stress levels well beyond levels previously anticipated in typical use, or in conventional qualification tests. A calibrated dynamic multiscale finite element model is used to evaluate the stresses at the relevant failure sites. Utilizing the local stress at each failure site, a fatigue damage modeling approach is proposed to predict the interaction of the competing failure mechanisms in MEMS components. The proposed damage model is based on the deviatoric stress (or strain) at the failure site and uses a hydrostatic stress correction factor to address the influence of mean stress (depending on component orientation). The model estimates the damage accumulation rate for a given stress condition and integrates the accumulated damage over the entire response history. This approach makes it possible to address the influence of the post-impact transient response on fatigue damage accumulation. The damage-model constants are determined for each failure site of interest by relating the failure data to the corresponding stress/strain metrics. Damage modeling results are not only capable of matching the lifetimes of MEMS components in drop testing, but also provide an explanation of transitions in dominant failure sites observed in MEMS assemblies under different drop conditions.

The Effect of Cryogenic Treatment on Microstructure and Mechanical Response of AISI D3 Tool Steel Punches

Recently, deep cryogenic treatment is performed to improve the mechanical responses (wear, hardness, fatigue, and thermal conductivity) of various steel components. Researchers have tried to evaluate the eco-friendly and nontoxic process to optimize the parameters. Cold-shearing punches used to manufacture various holes that undergo severe impact loading and wear in the metal forming process. This study concerns the effect of soaking time (24 hr, 36 hr) at liquid nitrogen temperature (−145 °C) during the deep cryogenic treatment on the microstructural changes which are carbide distribution and retained austenite percentage of AISI D3 tool steel punches. It was shown that the deep cryogenic treatment reduces retained austenite and enhanced uniform distribution of carbide particles. It is concluded that for significantly improved punch life and performance, it is an advisable application of 36 hr deep cryogenic treatment.

A hybrid model for prediction of ground-borne vibration due to discrete wheel/rail irregularities

A hybrid model for the prediction of ground-borne vibration due to discrete wheel and rail irregularities, such as wheel flats, dipped welds and insulated rail joints, is presented. The hybrid model combines the simulation of vertical wheel–rail contact force in the time domain, accounting for parametric excitation due to sleeper periodicity and impact excitation induced by loss of wheel–rail contact, and calculation of ground-borne vibration in the frequency–wavenumber domain considering a layered soil model. The model is demonstrated by investigating the influence of wheel flat size and vehicle speed on maximum vertical wheel–rail contact force and free field ground vibration. It is shown that magnitudes of impact load and ground vibration are increasing with increasing wheel flat length (and depth), but the influence of vehicle speed is not as evident. Higher vehicle speeds often lead to loss of wheel–rail contact and severe impact loads but the frequency content of such impact loads is shifted to higher frequencies which may be less significant for ground vibration.

Compressive Behavior of a Polyurea Elastomer

The application of elastomeric coatings for improving the ability of already existing structures to dissipate the energy released by impact events has been investigated by many researchers in the past decade and is today an area of considerable interest. In recent years, polyurea has been successfully applied as a coating material for enhancing the impact protection of buildings and it has also demonstrated a considerable improvement of the survivability of metallic and non-metallic structures subjected to severe shock and impact loading conditions. Given its remarkable properties in terms of impact energy mitigation, life endurance and corrosion resistance, this material is currently of interest for its application in many fields of engineering. This paper presents and discusses the results of the mechanical characterization conducted on a polyurea elastomer fabricated following two different procedures and subjected to varying strain rates of compression load. The tests were conducted to verify the sensitivity of the material behavior to the varying loading conditions and to verify how the fabrication of the material in the laboratory can influence the test results.

Material Behaviors of PBX Simulant with Various Strain Rates

This paper is concerned with the material behaviors of PBX(Polymer Bonded eXplosive) simulant at various strain rates ranging from 0.0001/sec to 3150/sec. Material behaviors of PBX at the high strain rates are important in the prediction of deformation modes of PBX in a warhead which undergoes severe impact loading. Inert PBX stimulant which has analogous material behaviors with PBX was utilized for material tests due to safety issues. Uniaxial compressive tests at quasi-static and intermediate strain rates were conducted with cylindrical specimen using a dynamic materials testing machine, INSTRON 8801. Uniaxial compressive tests at high strain rates ranging from 1200/sec to 3150/sec were conducted using a split Hopkinson pressure bar. Deformation behaviors were investigated using captured images obtained from a high-speed camera. The strain hardening behaviors of PBX simulant were formulated by proposed strain rate-dependent strain hardening model.

On the residual energy toughness of prestressed concrete sleepers in railway track structures subjected to repeated impact loads

Installed as the crosstie beam support in railway track systems, the prestressed concrete sleepers (or railroad ties) are designed in order to carry and transfer the wheel loads from the rails to the ground. It is nowadays best known that railway tracks are subject to the impact loading conditions, which are attributable to the train operations with either wheel or rail abnormalities such as flat wheels, dipped rails, etc. These loads are of very high magnitude but short duration, as well as there exists the potential of repeated load experience during the design life of the prestressed concrete sleepers. These have led to two main limit states for the design consideration: ultimate limit states under extreme impact and fatigue limit states under repeated impact loads. Prestressed concrete has played a significant role as to maintain the high endurance of the sleepers under low to moderate repeated impact loads. In spite of the most common use of the prestressed concrete sleepers in railway tracks, their impact responses and behaviours under the repetitions of severe impact loads are not deeply appreciated nor taken into the design consideration. This experimental investigation was aimed at understanding the residual capacity of prestressed concrete sleepers in railway track structures under repeated impact loading, in order to form the state of the art of limit states design concept for prestressed concrete sleepers. A high-capacity drop weight impact testing machine was constructed at the University of Wollongong as to achieve the purpose. Series of repeated impact tests for the in-situ prestressed concrete sleepers were carried out, ranging from low to high impact magnitudes. The impact forces have been correlated against the probabilistic track force distribution obtained from a Queensland heavy haul rail network. The impactdamaged sleepers were re-tested under static conditions in order to evaluate the residual energy toughness in accordance with the Australian Standard. It is found that a concrete sleeper damaged by an impact load could possess significant reserve capacity sufficient for resisting the axle load of about 1.05 to 1.10 times of the design axle loads. The accumulative impact damage and residual energy toughness under different magnitudes of probabilistic impacts are highlighted in this paper. The effects of track environment including soft and hard tracks are also presented as to implement design guidance related to the serviceability or fatigue limit statesdesign.

A novel numerical strategy for the simulation of irregular nonlinear waves and their effects on the dynamic response of offshore wind turbines

We present a novel numerical procedure for the prediction of nonlinear hydrodynamic loads exerted on offshore wind turbines exposed to severe weather conditions. The main feature of the proposed procedure is the computational efficiency, which makes the numerical package suitable for design purposes when a large number of simulations are typically necessary. The small computational effort is due to (i) the use of a domain-decomposition strategy, that, according to the local wave steepness, requires the numerical solution of the nonlinear governing equations only on a limited number of reduced regions (sub-domains) of the whole space–time domain, (ii) the choice of the particular numerical method for the spatial discretization of the governing equation for the water-wave problem. Within the potential flow assumption, the Laplace equation is solved by means of a higher-order boundary-element method (HOBEM). For the time evolution of the unsteady free-surface equations the 4th-order Runge–Kutta algorithm is adopted. The compound solver is successfully applied to simulate nonlinear waves up to overturning plunging breakers, that may cause severe impact loads on the wind turbine substructure.Emphasis is finally given to wind turbine exposed to realistic environmental conditions, where the proposed tool is shown to be capable of capturing important nonlinear effects not detected by the linear models routinely adopted in the design practice.