Mechanical Impact Loading Research Articles

Analysis of the destruction of a die insert used in the industrial process of hot die forging to produce a yoke forging

The article performs an analysis of the destruction of forging dies (with two impressions for a double system) used in the industrial process of forging on a hydraulic hammer to produce a yoke forging with a complex geometry. A detailed analysis was performer on one of the lower dies made of non-standard hot chromium-molybdenum-vanadium tool steel, selected for the tests due to its premature damage (a crack) and relatively low durability equalling only 1200 forgings, that is 600 forged elements. Based on the performed complex studies (surface scanning, microhardness tests, microscopic tests, numerical modelling, impact strength trials) it was demonstrated that the most dangerous destruction mechanism for the analyzed process is mechanical cracking and thermo-mechanical fatigue. As a result of the tool working under extreme conditions (high cyclic mechanical impact loads as well as thermal loads), the most intensive damage of the roughing pass, caused by thermal fatigue and abrasive wear, takes place in the areas of complex geometry as well as intensive flow of the forging material on the radii of the roundings. In turn, in the case of the finishing pass, we observe mechanical fatigue cracking of the tool in the areas of stress and high pressure concentration. The results of FEM modelling combined with the results of a microstructural analysis made it possible to determine the causes of the formation of cracks in the working area of the die, which included cyclic high thermal and mechanical loads as well as abrasive wear as a result of intensive flow of the forging material. Within the conducted studies, directions of further investigations were also proposed in order to improve the durability of the examined tool. Additionally, the observed high tendency of the tool material to crack, based on thermal expansion and impact tests and the determination of the crack resistance coefficient K1C, led to the proposal of an alternative material with higher impact strength.

Analysis of the damage effects of carbon fiber composites under the mechanical impact loads of lightning based on a modified simulation calculation method

Mechanical effects contribute significantly to the multiphysical damage of carbon fiber-reinforced polymer (CFRP) composites induced by high-amplitude impulse lightning currents. In this paper, the mechanical impact loads (MILs) of lightning are decomposed into acoustic shock waves from arc channel expansion (AESW), electromagnetic force (EMF), and shockwave overpressure from surface explosion (SESW). A 3D finite element mechanical damage model of laminates was established based on the Hashin–Yeh initial creation and modified stiffness degradation matrix. The model was verified by comparison with pure mechanical impacts. The dynamic response and damage modes of laminates subjected to AESW, EMF, SESW, and MILs were studied and compared. The MILs are exponentially related to the current intensity. The damage effect of laminates under MILs is inversely related to the impact radius. The comparison shows that the effect of the EMF gradually exceeds that of the AESW as the current peak increases and its value is approximately twice that of the latter when the current peak Ip exceeds 165 kA. In contrast, SESW is the primary cause of the damage effect. Over 70 % of the deformation contribution to laminates under MILs comes from SESW (Ip = 165 kA). Furthermore, the strongest SESW is induced by the insufficient thermal conductivity of the CFRP laminates.

Wing strike reduction for small fixed wing uncrewed aerial vehicles

This work presents the development of a leading edge strike resilient system for small, fixed wing unmanned aerial vehicles. This method uses passive, mechanically-linked wing sweep motion with a spring and buckling strip in parallel. Additive manufacturing is leveraged to prototype a geared substructure where rotation is resisted by a buckling strip and wing position is restored after impact by a linear spring. Experimental validation of the mechanism is conducted via drop-tower testing. For a rigid configuration the yaw impulse associated with impact grows with impact speed, while yaw impulse is thresholded by the yaw alleviation system. For the tested cases, impact moment is reduced by approximately 50% compared to the rigid case. A wind tunnel model was created to study the impact loading and changes in aerodynamic loads as the wings sweep backward and return forward after impact. Flight experimentation was conducted for symmetric and asymmetric impacts with manual flight recovery after impact while flying at 31 m/s at 2.4 m altitude. In the laboratory and in flight, mechanical impact loading on the vehicle is significantly reduced at a variety of airspeed and impact speeds with aerodynamic loading shown to damp the detrimental moments associated with leading edge strike.

Dispersion of Carbon Nanotubes Improved by Ball Milling to Prepare Functional Epoxy Nanocomposites

There has been an increase in interest in developing functional polymer composites based on green chemistry principles. The purpose of this study was to investigate the preparation of functional epoxy/carbon nanotube nanocomposites using ball milling methods. In contrast to mechanical mixing, ball milling promoted good dispersion of CNTs within the epoxy matrix, thereby improving their mechanical properties and electrical conductivity. In epoxy nanocomposites with ball milling, Young’s modulus and tensile strength were increased by 653% and 150%, respectively, when CNT loading was 1.0 vol%. Additionally, the ball milling of CNTs improves their dispersion, resulting in a low percolation threshold at 0.67 vol%. The epoxy/CNT film sensor that was produced using the ball milling approach not only exhibited high reliability and sensitivity to mechanical strains and impact loads, but also possessed the ability to self-detect damage, such as cracks, and accurately locate them. This study marks a notable milestone in the advancement of functional epoxy/CNT composites through the ball milling approach.

Developing functional epoxy/graphene composites using facile in‐situ mechanochemical approach

AbstractThe awareness of developing eco‐friendly polymer composites via green chemistry attract much attention in the recent years. In the current work, we explore preparing functional epoxy/ graphene nanocomposites using mechanochemical approach. Graphene platelets (GnPs) were modified with long‐chain surfactant via high‐energy ball milling. Modified‐GnPs (m‐GnPs) promote the dispersion quality and interface strength with epoxy matrix leading to higher mechanical properties, and better electrical and thermal conductivity compared to unmodified GnPs system. At 2.0 vol% m‐GnPs, elastic modulus, tensile strength, and thermal conductivity of epoxy were improved by 889%, 163%, and 105%, respectively. In addition, percolation threshold of electrical conductivity was observed at 0.71 vol% m‐GnPs. Halpin‐Tsai micromechanical model was able to predict the elastic modulus of the epoxy/GnP nanocomposites. The model results were compared experimental measurements. Furthermore, the measurements showed epoxy/m‐GnP film possess high sensitivity to mechanical strains and impact loads. The current work gives a step forward to use mechanochemistry approach in the production of functional epoxy/graphene composites.

Stress wave propagation analysis of 2D-FGM axisymmetric finite hollow thick cylinder

In this paper, a numerical axisymmetric elastic stress wave propagation analysis of the 2D-FGM hollow thick finite cylinder has been performed. The new accurate material distribution model based on Mori-Tanaka scheme and third-order transition function for 2D-FGMs has been implemented in the graded finite element method with higher-order quadrilateral elements. A non-uniform impulsive pressure has been applied on the one-third of the top inner cylinder wall. Consequently, different wave velocities and reflections from the boundaries have been observed due to the graded distribution of material along with two directions. Moreover, the effects of two-dimensional material property distributions on the stress wave propagations and displacements through the cylindrical wall at different locations have been studied systematically. Normalized effective stresses based on von-Mises criteria has been performed in comparison with the internal impulsive pressure amplitude to provide a measure of the cylinder wall response to the mechanical impact loading, the effective stresses are nearly 2.5 times the internal pressure loading amplitude, closed to the impact location. According to the results, 2D material property gradations has effected the stresses significantly. Alternatively, desired stress values can be achieved through optimal design and appropriate choice of property distribution.

Experimental Investigation of Concrete Sandwich Walls with Glass-Fiber-Composite Connectors Exposed to Fire and Mechanical Loading

Precast concrete sandwich panels (PCSPs) are known for their good thermal, acoustic and structural properties. Severe environmental demands can be met by PCSPs due to their use of highly thermally insulating materials and non-metallic connectors. One of the main issues limiting the wider use of sandwich walls in construction is their unknown fire resistance. Furthermore, the actual behaviour of connectors and insulation in fire in terms of their mechanical performance and their impact on fire spread and the fire resistance of walls is not fully understood. This paper presents an experimental investigation on the structural and thermal behaviour of PCSPs with mineral-wool insulation and glass-fiber-reinforced polymeric bar connectors coupling two concrete wythes. Three full-size walls were tested following the REI certification test procedure for fire walls under fire and vertical eccentric and post-fire mechanical impact load. The three test configurations were adopted for the assessment of the connectors’ fire behaviour and its impact on the general fire resistance of the walls. All the specimens met the REI 120-M criteria. The connectors did not contribute to the fire’s spread and the integrity of the walls was maintained throughout the testing time. This was also confirmed in the most unfavourable test configuration, in which some of the connectors in the inner area of the wall were significantly damaged, and yet the structural connection of the concrete wythes was maintained. The walls experienced heavy heat-induced thermal bowing. The significant contribution of connectors to the stiffness of the wall during fire was observed and discussed.

CIRCULAR DOUBLE SKIN STAINLESS STEEL TUBULAR COLUMN FILLED WITH UHPFRC SUBJECTED TO IMPACT LOAD

Concrete filled steel tube (CFST) column is an important type of structural member and its protective design is essential to enhance its structural performance under various dynamic loads. Previously carried out studies on CFST columns tried to determine how to improve their structural response under various loadings, such as axial compression, lateral impact, blast, seismic, etc. Apart from investigations on transverse impact loading, the majority of the other studies on CFST under various loads established solutions and protective measures. Therefore, this study aim is to improve the performance of CFST under transverse impact loads. The geometrical and mechanical properties, boundary conditions, impact loading and dynamic explicit analysis employed in that study. This paper proposes a novel design in terms of cross-sectional configuration and smart materials to be applied on the CFST in order to improve its performance under lateral impact loading. The proposed investigation is exclusively numerical and its results were verified with the experimental results from literature. The considered three main variables were including (1) concrete-filled double skin steel tubular – CFDST with both first sandwich layer and internal carbon steel tube filled with normal strength concrete – NSC, (2) CFDST with first sandwich layer filled with Ultra High-Performance Fiber-Reinforced Concrete – UHPFRC. a. The parameters including failure modes, maximum mid-span deflection, and residual displacements were presented.

Reliability design of mechanical systems subjected to repetitive stresses

To enhance the design of mechanical systems, parametric Accelerated Life Testing (ALT) as a systematic reliability method is proposed as a way to evaluate the design of mechanical systems subjected to repeated impact stresses. It requires: (1) a parametric ALT scheme shaped on system BX lifetime, (2) a load inspection, (3) parametric ALTs with the associated design modifications, and (4) an assessment of whether the revised product design(s) reach the targeted BX life-time. We propose using a general life-stress model and sample size equation. A test example using both market data and parametric ALT was the redesign of a hinge kit system (HKS) in a refrigerator. To conduct parametric ALTs, a force and moment balance analysis was utilized. The mechanical impact loadings of the HKS were evaluated for an working refrigerator door. For the first ALT, the HKS failure happened in the crack/fracture of the kit housing and oil spilled from the damper when the HKS was disassembled. The failure modes and mechanisms constructed in the 1st ALT were similar to those of the unsuccessful samples found from the marketplace. The missing design parameters of the HKS included stress raisers such as corner roundings and the rib of the housing in HKS, the seal in the oil damper, and the material of the cover housing. In the second ALT, the cover housing fractured. The design defect of the cover housing in the HKS was the plastic material. As a corrective action plan, the cover housing was modified from plastic to aluminium. After the second ALT, the lifetime of the modified HKS was reassured to be B1 life 10 years with a yearly failure rate of 0.1%.

Mechanical Tests Applied to Structural Health Monitoring: An Overview of Previous Experience

Abstract Laboratory for Materials Strength Testing (LMST) has been conducting accredited mechanical research for aviation from 2003. Among accredited procedures are e.g. low and high cycle fatigue tests, fracture toughness tests and fatigue crack growth rate tests. The main goal of them is obtaining materials constants and characteristics. However knowledge how to conduct these tests could be used also in other applications, for instance in the work on development of Structural Health Monitoring systems (SHM). When cracks propagate in a controlled way in laboratory conditions, it allows verifying the operation of a single sensor or a network of sensors. In this paper, an overview of mechanical tests carried out at the Laboratory for Materials Strength Testing within Air Force Institute of Technology (AFIT) work on research and development of SHM systems is presented. Specimens prepared from materials such as aluminum alloys (among other withdrawn PZL-130 Orlik TC-II aircraft) and CFRP composite were tested under different mechanical loads, i.e., cycle and impact loads. In the presented research, both constant amplitude and spectrum loads were applied.

Anti-plane crack problem of a functionally graded piezoelectric materials strip with arbitrarily distributed properties

This paper treats the anti-plane crack problem of a functionally graded piezoelectric material (FGPM) strip with arbitrarily distributed properties. It is assumed that the elastic stiffness, piezoelectric constant, and dielectric constant of the FGPM vary continuously along the thickness of the medium, and the strip is under anti-plane mechanical and in-plane electric impact loadings. By using the Fourier transform and defining unknown discontinuous functions across the crack surfaces, the anti-plane crack problem of FGPM is reduced to a group of singular integral equations, which are solved numerically. The stress and electric displacement intensity factors are presented, and the influences of the nonhomogeneous and geometric parameters on stress and electric displacement intensity factors are also included.

Reliability design and case study of mechanical system like a hinge kit system in refrigerator subjected to repetitive stresses

To improve the reliability of mechanical systems with inherited faulty designs, a reliability methodology utilizing parametric accelerated life testing (ALT) is suggested. It consists of: 1) a parametric ALT plan, 2) a load analysis, 3) a tailored series of parametric ALTs with action plans, and 4) an evaluation of the final designs to ensure the design requirements are satisfied. This parametric ALT should help an engineer uncover the design parameters affecting reliability during the design process of a mechanical system. As a case study, the hinge kit system (HKS) of a door in a refrigerator was redesigned to improve its reliability. Using a force and moment balance analysis, the mechanical impact loads in closing the door of the HKS were calculated. During the first ALT, the kit housing in the HKS fractured and the oil damper leaked when the HKS failed. The faults in the design of the HKS included the weakness of the housing hinge kit and the oil sealing structure of the oil damper. In the second ALT, the hinge cover fractured due to the impact of the damper support. The material in the hinge cover in the HKS was changed from plastic to aluminum. After three rounds of parametric ALTs, the reliability of the new HKS was guaranteed to be a 10 year life with an accumulated failure rate of 1%.

Study of plant fibre composites with damage induced by laser and mechanical impacts

Abstract Polymer composite materials provide good strength to weight ratio and tailored mechanical properties thanks to the reinforcing fibres. Until recently, the need for taking into account the whole life cycle of a composite structure was neglected and only the service aspects were important. Today, the designers of a new composite structure have to take into account the environmental aspects from the sustainability of raw materials to the management of end life products. There are recycling issues related to the most popular composites. A solution for the recycling issue can be sought in green composites with reinforcing fibre originating from plants. The behaviour of eco-composites, when subjected to laser or mechanical impact loadings, is not well known yet. Short fibre composites were made with spruce fibres. Another set of samples was made of flax fibres. Also a woven hemp fabric-based eco-composite was investigated. A fully synthetic woven composite was used for comparison with green composites. Mechanical impacts were performed by means of a falling dart impact testing machine. Laser impacts were made with high power laser source. Four assessment techniques were employed in order to analyse and compare impact damage. Damage detection thresholds for each material and technique were obtained.

Elastic wave propagation in non-uniform rational B-spline rods under mechanical impact loading using an isogeometrical approach

One-dimensional elastic wave propagation under quadratic impact loading in a rod with a variable cross section and material distribution is the subject of this study. The material distribution of the problem under investigation as well as the variations of the geometry was elucidated with non-uniform rational B-spline (NURBS). The problem was analyzed employing the isogeometric approach in order to ensure precise modeling of the geometry. The effects of impact loading, cross sectional area, material distribution, and radial inertia on elastic waves were examined in this study. In addition, propagation, reflections, and propagation speed along the axis were investigated. It was observed that the speed was not constant along the axial direction. Also, the cross sectional area had more effect on the amplitude of the elastic wave than the radial inertia. Furthermore, it was concluded that the material distribution and radial inertia may influence the wave propagation speed.

A complete equation of state for polyethylene based on Helmholtz free energy

Polyethylene (PE) is an important kind of plastic, which plays a significant role as the shell material of the fuel capsule, light weight structural element subjected to intense mechanical impact and explosion load. And it is well accepted that semi-empirical three-term equation of state (EOS) is one of the most widely used EOSs in practical work. Therefore, studies of semi-empirical three-term EOS of PE are significant for accurately predicting and analyzing the physical processes and experimental results under high pressure compression. A semi-empirical three-term complete EOS of PE based on the model of Helmholtz free energy is established in this work. According to the EOS model, the Helmholtz free energy is composed of cold energy, thermal contribution of atoms and thermal excitation of electrons. The cold energy is calculated by using the Mie potential. The optical frequency branch of atomic vibration and the thermal contribution of electrons are neglected in the calculation at temperatures below 104 K. The parameters of Helmholtz free energy are calculated by using the shock Hugoniot data and thermal parameters at ambient state. And then, the application pressure range and reliability of the semi-empirical three-term EOS of PE are evaluated. Shock Hugoniot, shock wave temperature and Grneisen coefficient of PE are deduced from the EOS. The results show that shock Hugoniot and shock wave temperature are consistent well with the experimental data and the first-principle calculation in a pressure range of 150 GPa. Because the specific volume of PE does not change obviously in the melting and chain dissociation process, the assumption of linear Hugoniot relation of PE is valid for calculating the cold energy parameters. The calculation results deviate from the experimental results at about 150 GPa while the compression lasts up to the chemical bond dissociation pressure of PE. In addition, the value of buck modulus and its derivative with respect to pressure at zero pressure and temperature depend strongly on Hugoniot parameters. Therefore, the parameter of Helmholtz free energy in this work is only valid for compression. In conclusion, the Helmholtz free energy model and parameters can well reproduce the experimental data and reasonably describe the thermodynamic state of PE at its dissociation pressure. Moreover, it should be pointed out that a more refined model of phase transition and thermal contribution of atoms and electrons should be considered when extrapolated to higher pressure.

Probabilistic risk assessment of aircraft impact on a spent nuclear fuel dry storage

This paper proposes a systematic risk evaluation framework for one of the most significant impact events on an interim dry storage facility, an aircraft crash, by using a probabilistic approach. A realistic case study that includes a specific cask model and selected impact conditions is performed to demonstrate the practical applicability of the proposed framework. An event tree analysis of an occurred aircraft crash that defines a set of impact conditions and storage cask response is constructed. The Monte-Carlo simulation is employed for the probabilistic approach in consideration of sources of uncertainty associated with the impact loads onto the internal storage casks. The parameters for representing uncertainties that are managed probabilistically include the aircraft impact velocity, the compressive strength of the reinforced concrete wall, the missile shape factor, and the facility wall thickness. Failure probabilities of the impacted wall and a single storage cask under direct mechanical impact load caused by the aircraft crash are estimated. A finite element analysis is applied to simulate the postulated direct engine impact load onto the cask body, and a source term analysis for associated releases of radioactive materials as well as an off-site consequence analysis are performed. Finally, conditional risk contribution calculations are represented by an event tree model. Case study results indicate that no severe risk is presented, as the radiological consequences do not exceed regulatory exposure limits to the public. This risk model can be used with any other representative detailed parameters and reference design concepts for other comparable direct or indirect impact conditions onto the cask body, which may provide an efficient way to investigate storage facility capacity to withstand an aircraft crash and thereby protect public health.

Structural analysis of a metal spent-fuel storage cask in an aircraft crash for risk assessment

Evaluations of the impact resistance of a dry storage cask under mechanical impact loadings resulting from a large commercial aircraft crash have become an important issue for designers and evaluators, in order to promote interim dry storage activities and to evaluate design safety margins. This study presents a method to evaluate the structural integrity of a generic metal cask subjected to various mechanical loading conditions, which represent aircraft engine impacts, on different locations of the cask body. Thirty representative impact conditions are analyzed to provide a comprehensive evaluation of cask damage response. The applied engine impact load–time functions were carefully re-derived by utilizing CRIEPI’s proposed curve through Riera’s approach for six impact velocities, and applied to five locations on a freestanding cask: lateral impacts on the lower half, center of gravity, and upper half of the cask body, corner impact on the lid closure, and vertical impact on the center of the lid closure. A nonlinear dynamic finite element analysis is performed to evaluate the dynamic response of the cask lid closure system and to calculate the lid gaps. The release fractions from the cask to the environment for each impact condition are preliminarily estimated by referring to a proposed methodology from literature. It is believed that this paper presents a systematic process to connect the mechanical analysis of a cask response at the moment of aircraft engine impact with its radiological consequence analysis.

Simulation Based Reduction of the Impact Load Occurring in the Moment of Cutting Edge Entrance in Order to Prolong Tool-Life

High mechanical impact loads in interrupted or inhomogeneous machining processes frequently lead to spontaneous fracture of the cutting edge. Even modern cutting materials cannot provide a combination of high enough hardness and toughness that is capable of preventing this sort of tool failure. Such machining conditions therefore remain difficult and further investigations, aiming to reduce the impact load of the cutting tool in order to enhance tool-life, are necessary. A simulation model of the impact situation, that serves to optimize a force conducting structure with regard to elasticity, damping properties and resulting force peaks, was developed and is presented in this paper. Furthermore measurement devices were composed that are needed for high-resolution recording of impact forces without repercussions and for verification of the elaborated simulation model. It could be shown that mechanical damping of the cutting tool can lead to reduced impact forces on the cutting edge, which in turn should lead to longer tool life.

Mechanical Energy Dissipation in a Multifunctional Battery System

ABSTRACTIn this paper, we report on a multifunctional battery assembly, which possesses a balanced combination of energy storage capability and resistance to electrical failure under mechanical impact loading. The Granular Battery Assembly (GBA) presented here exhibits a mechanical response that emerges from features of granular and cellular media. We demonstrate that for the specific GBA embodiment considered in the present study, the electrical reliability following a mechanical loading event is substantively increased compared to that of plain battery cells. The increased reliability is due to the sacrificial material elements interspersed between the battery units, attributing energy absorption and local stress limiting.

Traffic seismicity loaded historical building frequency parameters identification due to most commonly used truck in Slovakia

Experimental investigation and combination with numerical modelling is one of the progressive method in many scientific areas. The structural dynamics including traffic seismicity effects are also becoming an increasing topic. The aim of this paper was to realize the numerical analysis of heritage Upper Gate in Modra - Slovakia and FEM simulation of the lorry T-815 natural vibration. These subsystems are dominant processes in traffic seismicity vibration effects in buildings. For this purpose the variants of FE model by computing program Scia engineering has been created for building and software ADINA for lorry. These models are important for the assessment of the dynamic vibration transmissibility due to mechanical impact load properties. The results of this simulation was evaluated in frequency area. Next part of the investigation was the realisation of the experimental measurement. The results obtained from the experiment were compared with FE analysis. Using of the theoretical analysis, experimental procedures results and FEM simulation of the natural vibration it seem to be the practical application for engineering practice in prediction and assessment buildings vibration due to seismicity induced by traffic.