Severe Impact Loading Research Articles

Design Optimization of Truck Body Floor for Heavy Loading

Construction and mining segment in India has picked up pace in recent years. Due to this, equipments such as tippers, excavators and loaders are in great demand. Function of tipper trucks is to combine the two tasks of dumping and haulage. Truck Body Floor which is used for this purpose has been designed in a conventional way since its inception. Normal conventional method of floor construction is a sandwich floor with layers of steel floor on top and bottom and a layer of wood in between. Scope of this paper is to optimize the design of conventional truck body floor design considering heavy & impact loading in mines which damages the floor. Thus this demands the need of heavy duty impact resistance floor which replaces the normal conventional sandwich construction. Hence new concept of single layer heavy duty floor has been embarked upon with high strength material which will be able to resist severe impact loads and also results in weight reduction with various other advantages.

Ultimate Impact Resistance and Residual Toughness of Pre-Stressed Concrete Railway Sleepers

The pre-stressed concrete sleepers (or railroad ties), which are installed in railway track systems as the crosstie beam support, are designed to carry and transfer the wheel loads from the rails to the ground. It is well known that railway tracks are subject to 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. In addition, there exists the potential of repeated load experience during the design life of pre-stressed concrete sleepers. Pre-stressed concrete has played a significant role in maintaining the high endurance of sleepers subjected to low to moderate repeated impact loads. In spite of the common use of pre-stressed concrete sleepers in railway tracks, their impact response and behaviour under repetitions of severe impact loads are not deeply appreciated, nor taken into consideration in design. This experimental investigation was aimed at understanding the residual capacity of pre-stressed concrete sleepers in railway track structures under ultimate impact loading, in order to develop state of the art limit states design concepts for pre-stressed concrete sleepers. A high-capacity drop weight impact testing machine was constructed at the University of Wollongong to achieve this purpose. A series of severe impact tests on in-situ pre-stressed concrete sleepers was carried out, ranging from low to high impact magnitudes. The impact energy was evaluated in relation to the drop heights. The impact-damaged sleepers were re-tested under static conditions in order to evaluate the residual fracture toughness in accordance with the Australian Standard. It was found that a concrete sleeper damaged by an impact load could possess significant reserve capacity sufficient for resisting about 1.05 to 1.10 times the design axle loads. The impact behaviour and residual fracture toughness under different magnitudes of impacts are highlighted in this paper. The effects of track environment, including soft and hard tracks, are also presented together with a discussion related to the ultimate limit states design.

Optimisation of a beam in bending subjected to severe inertia impact loading

This paper summarises an optimal analytical study of a bar when it is subjected to shock inertia loading such that the severe bending causes permanent yielding. The findings are related to a practical case study application and help explain the necessary actions that have to be taken to minimise the impact damage. The analysis relates the sudden strain energy which the bar gains following an impact (when either the stationary bar is collected by a body moving with substantial momentum or alternatively when the moving bar is suddenly brought to a halt) and establishes the bending strength as a function of mass, stiffness and other kinematic conditions. The optimal analysis results in a surprising paradox which is borne out in the actual detail design solution to a critical component which had caused major maintenance problems in the braking system of a railed vehicle. The study reveals some interesting findings relating to the best bar configuration in terms of geometrical design, support locations and material choice.

Dynamic Crack Propagations in Prestressed Concrete Sleepers in Railway Track Systems Subjected to Severe Impact Loads

Prestressed concrete sleepers (or railroad ties) are the crosstie beam support in railway track systems. They are designed and constructed under flexural constraints in order to carry and transfer the dynamic wheel loads from the rails to the ground. Under perfect wheel and rail conditions, the dynamic loading on railway tracks could be treated as a quasi-static load using a dynamic impact factor. The current design method for the prestressed concrete sleepers taking into account the quasi-static effect is based on allowable stress where crack initiation is not permitted. In reality, the impact events are often detected due to the uncertainties of wheel or rail abnormalities such as flat wheels, dipped rails, etc. These loads are of very high magnitude but short duration. Over the design life span of the prestressed concrete sleepers, there exists the feasibility of extreme and repeated impact loading events. These have led to two proposed limit states for the consideration of structural engineers: ultimate limit states and fatigue limit states. Prestressing techniques have been long used to maintain the high endurance of the sleepers under repeated impact cycles. In spite of the most common use of the prestressed concrete sleepers, their impact behavior and capacity under the repetitions of severe impact loads are unclear. This paper presents the experimental investigation aimed at understanding the dynamic crack propagations in prestressed concrete sleepers in railway track structures under repeated impact loading. The impact forces have been correlated against the probabilistic track force distribution obtained from an Australian heavy haul rail network. The effects of track environment including soft and hard tracks are highlighted in this paper.

Train-Induced Vibrations on Urban Metro and Tram Turnouts

In contrast to standard track, where train-induced vibrations are mainly related to track irregularities, the dynamic response of turnouts is dominated by the nonuniform geometry of wheel-rail contact and variations in track flexibility. Such peculiarities are responsible for the development of strong vibrations during train passage. At the point of rail intersection (heart), where a gap is unavoidable to provide the necessary wheel flange clearance, the system is subjected to severe impact loading, critical for the design and maintenance of railway tracks. Especially in the case of urban turnouts, the vibration levels are also directly related to the exerted noise nuisance. This paper presents two analysis methods to simulate train-turnout interaction. The first is based on a multibody model of the trainset and of wheel-rail contact, utilizing a simplified finite element model for the turnout. The second focuses on the details of the turnout, which is modeled with three-dimensional finite elements, utilizing a simplified model to compute impact loading due to wheel passage over the flange-way gap. The two models are validated against line measurements on three different urban metro and tram networks. A parametric analysis is conducted to investigate the role of soil-structure interaction, which is shown be important for the dynamic response of the system.

Effects of train impacts on urban turnouts: Modelling and validation through measurements

Train–track interaction at turnouts is a main issue in the design and maintenance of railway systems. Due to the particular geometry of wheel–rail contact and to the sudden variation of track flexibility, severe impact loads may occur during train passage over the turnout. In this paper, two different modelling approaches to reproduce train–turnout interaction are proposed and compared. A first technique, developed by Politecnico di Milano, is based on a detailed multi-body model of the trainset and of wheel–rail contact, whereas for the turnout structure a simplified finite element model is used. The second modelling technique, developed by the National Technical University of Athens, relies on a detailed finite element model of the turnout, while a simplified model is used to compute impact loading due to wheel passage. In this paper the two methods are validated trough comparison with line measurements performed on turnout systems from three different urban railway networks.

Impact Response of Titanium and Titanium Boride Monolithic and Functionally Graded Composite Plates

Functionally graded materials have gained significant interest within the research community in recent years. Functionally graded materials are advanced composites in which local material properties are tailored to suit application requirements by altering the volume fraction ratios of two or more constituents. In this article, the behavior of metal-ceramic functionally graded material plates under low-velocity, medium-energy impact loading is considered using experimental and computational techniques. A series of impact tests were conducted on monolithic and functionally graded plates composed of titanium and titanium boride. The tests were performed using a vertical drop test apparatus in which highly controlled impacts of up to 108 J were delivered to the center of the top surface of each plate. The opposing bottom surface of each plate was instrumented with strain gauges wired into a high-speed data acquisition system to collect strain histories throughout the duration of the impact event. A sophisticated finite element model of the test was constructed to simulate the conditions of the experiments. Two distinct material models were used in the finite element analyses to study the monolithic and graded plates. The first model used analytical expressions based on the local volume fractions of the constituents to generate homogenized-material properties for the mixtures of titanium and titanium boride. The second model randomly distributed cells containing titanium elements and titanium boride elements constrained to satisfy local volume fraction ratios in the monolithic and graded specimens. The strain histories from the experiments were compared with the analogous solutions from the finite element model analyses to validate the computational models used in the study. Specifically, analyses with respect to historical trends, maximum strain magnitudes, and strain-rate effects were performed to gain insight into the impact response of the plate structures. The key contribution is validation of functionally graded material models and a computational framework for studying the impact response of functionally graded material plates as a foundation for investigations of more severe impact loads.

Experimental and numerical studies for evaluating dynamic behaviour of pre-stressed concrete sleepers subject to severe impact loading

Experimental and numerical studies for evaluating dynamic behaviour of pre-stressed concrete sleepers subject to severe impact loading

Evaluation of typical concrete material models used in hydrocodes for high dynamic response simulations

Abstract With the advancement of the computational capabilities, it is now possible to carry out high fidelity simulation of the complex responses of concrete structures subjected to severe shock and impact loads such as those generated by an explosion. A reliable simulation of the detailed response can play a significant role in the understanding of the physical mechanisms and the development of practical design guidelines based on parametric investigations using validated computational models. Among other influencing factors, a fundamental requirement in simulating concrete structures under shock and impact loadings is a realistic modelling of the behaviour of the concrete material under complex and rapid loading conditions. This paper presents a comprehensive evaluation study of several widely used concrete material models. The model formulations are scrutinized and numerical tests are carried out to examine their actual performances under various loading conditions. Comments on the limitations and the appropriate use of these models are given. Furthermore, a physical explosion test on a concrete slab is simulated to demonstrate the behaviour of the material models in a real application environment. Comparison of the results shows that the Concrete Damage Model implemented in LS-DYNA (material #72) describes the concrete response satisfactorily. Using a modified parameter setting, the RHT model implemented in AUTODYN also exhibits a generally acceptable behaviour.

Simulation of dynamic interaction between train and railway turnout

Dynamic train–track interaction is more complex in railway turnouts (switches and crossings) than that in ordinary tangent or curved tracks. Multiple contacts between wheel and rail are common, and severe impact loads with broad frequency contents are induced, when nominal wheel–rail contact conditions are disturbed because of the continuous variation in rail profiles and the discontinuities in the crossing panel. The absence of transition curves at the entry and exit of the turnout, and the cant deficiency, leads to large wheel–rail contact forces and passenger discomfort when the train is switching into the turnout track. Two alternative multibody system (MBS) models of dynamic interaction between train and a standard turnout design are developed. The first model is derived using a commercial MBS software. The second model is based on a multibody dynamics formulation, which may account for the structural flexibility of train and track components (based on finite element models and coordinate reduction methods). The variation in rail profile is accounted for by sampling the cross-section of each rail at several positions along the turnout. Contact between the back of the wheel flange and the check rail, when the wheelset is steered through the crossing, is considered. Good agreement in results from the two models is observed when the track model is taken as rigid.

Effects of Vehicle Impact Velocity and Front-End Structure on Dynamic Responses of Child Pedestrians

To investigate the effects of vehicle impact velocity and front-end structure on the dynamic responses of child pedestrians, an extensive parametric study was carried out using two child mathematical models at 6 and 15 years old. The effect of the vehicle impact velocity was studied at 30, 40, and 50 km/h in terms of the head linear velocity, impact angle, and head angular velocity as well as various injury parameters concerning the head, chest, pelvis, and lower extremities. The variation of vehicle front-end shape was determined according to the shape corridors of modern vehicles, while the stiffness characteristics of the bumper, hood edge, and hood were varied within stiffness corridors obtained from dynamic component tests. The simulation results show that the vehicle impact speed is of great importance on the kinematics and resulting injury severity of child pedestrians. A significant reduction in all injury parameters can be achieved as the vehicle impact speed decreases to 30 km/h. The head and lower extremities of children are at higher injury risks than other body regions. Older children are exposed to higher injury risks to the head and lower leg, whereas younger ones sustain more severe impact loads to the pelvis and upper leg. The results from factorial analysis indicate that the hood-edge height has a significant effect on the kinematics and head impact responses of children. A higher hood edge could reduce the severity of head impact for younger children, but aggravate the risks of head injury for older ones. A significant interaction exists between the bumper height and the hood-edge height on the head impact responses of younger child. Nevertheless, improving the energy absorption performance of the hood seems effective for mitigating the severity of head injuries for children.

Failure analysis of a cold-extrusion punch to enhance its quality and prolong its life

A cold-extrusion punch used to manufacture sockets undergoes severe impact loading and severe wear in the metal forming process. Failure in the cold-extrusion punch frequently occurs and is difficult to avoid. Owing to the complicated manufacturing process and the lack of service history of the cold-extrusion punch, detecting the major causes of the punch failure is difficult. Therefore, this study analyzes the major causes of the failure of a cold-extrusion punch by initially examining the mechanical properties of the cold-extrusion punch to identify defects in its related performance. Eliminating such defects is necessary to enhance the quality of the cold-extrusion punch. To determine the major causes of failure of the cold-extrusion punch, the characteristics of the failure are compared with those of well-known failure mechanisms, including the macro- and micro-characteristics of failure mechanisms. By closely examining the results of the mechanical properties and the results of the failure analysis of a cold-extrusion punch, this study proposes an effective method to avoid punch failure and prolong the punch life.

Solidification characteristics of atomized white cast iron powders

In recent years, interest in rapid solidification has been increasing and the subject has received extensive study. When compared with conventional solidification methods, rapid solidification technique produce microstructures with refined grain size, increased solubility of alloying element and impurities, and reduced levels of segregation. For many alloys, these effects lead to beneficial improvements in mechanical and other properties. White cast irons are commonly used engineering materials. However, cast iron components usually have a poor ductility and toughness under some severe conditions, for example, cyclical and impact loading. White cast irons are normally regarded as brittle materials. This lack of ductility is generally attributed to the presence of a large volume fraction of carbides which are distributed in a rather massive form within a ferrite matrix. Recent research shows that the large eutectic carbides in white cast iron can be refined through rapid solidification technology (RST). It is important to study the structural characterization of atomized powders since they have a direct effect on the properties of powder compacts. The present work is concerned with the morphology and microstructure of atomized low alloyed white cast iron powders.

USS TRI-TEN

Abstract USS TRI-TEN is a high-strength low-alloy steel primarily intended to reduce weight, or to increase durability in applications involving cold forming, welding, and moderately severe impact loading. This datasheet provides information on composition, physical properties, elasticity, tensile properties, and compressive and shear strength as well as fracture toughness. It also includes information on corrosion resistance as well as forming, heat treating, machining, joining, and surface treatment. Filing Code: SA-46. Producer or source: United States Steel Corporation. Originally published August 1956, revised May 1973.

Influence of boron on the structure and properties of hard-facing alloys

1. In wear-resistant facings boron dissolves in chromium carbide, forming compounds with chromium and iron (borides) distributed in the eutectic. 2. The brittle and hard borides increase the hardness and brittleness of the alloy, which explains the embrittlement of facings when boron is added. 3. Facings working under severe impact loading conditions should contain no more than 0.2% B (for facings with no more than 20% Cr and no more than 1.6%C). Up to 0.6–0.8% B can be added to facings working under abrasive wear conditions without impact loading.

Test on the Dynamic Mechanical Performance of the Power Shovel

As the power shovel must deal with the earth in its work, it receives severe impact loads which vary according to the digging conditions and operating method. These impact loads are very difficult to grasp theoretically and there have been only a few theses ever written on this subject. This report deals with analysis of oscillogram recordings taken on various factors concerning power shovels in actual work. The points clarified by this study were as follows. (1) Degree of impact torque applied on the power shovel during digging, swing and travelling. (2) Reduction of impact and improvement of working properties by wing a fluid power transmission device. (3) Adaptability of secondary impedance system motor for the shovel work of an electric power shovel.

Application of Impregnated Fabric Bearings to Roll Necks

Abstract The suitability of celoron for roll-neck bearings has led to widespread use of the product in that field. Its resilience allows bearings to absorb severe impact loads without permanent deformation. Celoron bearings are most commonly lubricated with water, in which case the rate of wear and the power consumed in friction are much less than those of metal bearings. The application of a superior lubricant such as oil or grease improves their performance appreciably. Celoron bearings serve most efficiently on highly polished roll necks, and they have produced substantial power savings in comparison with metal bearings, and their life in numerous installations has been found to be many times that of metal bearings.