Collapse Force Research Articles

The energy absorption control characteristics of Al thin-walled tube under quasi-static axial compression

Abstract Crushing energy should sufficiently be absorbed in order to secure the protections of passengers in a car accident. There have been a lot of studies on the crushing energy absorption of a basic structure in automobiles. In this paper, the purpose concerns the crashworthiness of the widely used vehicle structure, square thin-walled tubes, which are excellent on the point of the energy absorbing capacity. An experimental investigation was carried out to study the energy absorption characteristics of thin-walled square tubes subjected to quasi-static axial loading to develop the optimum structural members. Notch shapes and structure modification applied to structural design have nowadays been used to keep up the efficiency of energy absorption. Such ideas may result in the reduction of structural stiffness and buckling or collapse can easily be done in collision. The controller is introduced to improve and control the absorbed energy of thin-walled square tubes in this paper. To predict and control the energy absorption, controller is designed in consideration to its influence such as height, thickness, width ratio, in this study. The absorption energy and mean collapse force of square tubes was increased by 15–20% in using the controller and energy absorbing capability of the specimen was slightly changed by change of the high controller's height.

Quantitative Measurement of Pattern Collapse and Particle Removal Force

The pattern collapse and the particle removal force should be quantitatively understood and measured to develop the effective cleaning process without pattern damages. The method of measuring these forces by atomic force microscope (AFM) was introduced in this paper. Pattern collapse forces of a silicon oxynitride (SiON), silicon oxide (SiO2) and photoresist (PR) line pattern were measured. The particle removal force was measured on a 100 nm PSL particle on silicon. The force for pattern collapse increased linearly as a function of pattern width. PR pattern requires a smaller force than the SiON and SiO2 pattern at the same line width. Particle removal force of aged PSL on hydrophilic Si surface was two orders smaller than the collapse force of same size of patterns.

Quantitative Measurement of Pattern Collapse Force and Particle Removal Force

not Available.

Experimental observations of an 8 m/s drop test of a metallic helicopter underfloor structure onto water: Part 2

This is the second part of a two-part paper that describes the experimental observations for two similar sections of floor that were dropped onto both hard and water surfaces at 8 m/s, as part of one experimental campaign. The current paper provides an assessment of a simple box-beam under floor structure typically found in metallic helicopters and provides an overview of the failure modes and the collapse mechanism observed when dropped onto water at 8 m/s, as well as providing quantitative data for the skin deflections observed. The results demonstrate that the lack of frame and intersection joint collapse is a common feature, which is caused by the high failure strength of the existing construction, together with the inability of the skin to generate membrane loads that are sufficiently large to trigger progressive collapse within the structure. It is therefore recommended to reduce the collapse force of the structure through the use of geometry, material type, and inclusion of triggers. However, the caveat with this approach is that if the failure strength is optimized for a water impact, a poor crashworthy response may occur during a hard surface impact. The current paper discusses three main limitations with the design, which are heavily interrelated, as improvements in frame and joint collapse cannot be achieved without considering developing the ductile behaviour of the skin. However, maintaining skin integrity will be critical to maintain the floatation capabilities of the helicopter. The current paper recommends that a next generation design should encompass a passive dual role capability for both hard and soft surface impacts, by being able to degrade the localized strength depending upon the type of surface encountered. This will significantly improve the crashworthy response of a metallic under floor structure and have a significant impact on improving occupant survivability for an impact on water.

Fluorescence correlation spectroscopy shows that monomeric polyglutamine molecules form collapsed structures in aqueous solutions.

We have used fluorescence correlation spectroscopy measurements to quantify the hydrodynamic sizes of monomeric polyglutamine as a function of chain length (N) by measuring the scaling of translational diffusion times (tau(D)) for the peptide series (Gly)-(Gln)(N)-Cys-Lys(2) in aqueous solution. We find that tau(D) scales with N as tau(o)N(nu) and therefore ln(tau(D)) = ln(tau(o)) + nuln(N). The values for nu and ln(tau(o)) are 0.32 +/- 0.02 and 3.04 +/- 0.08, respectively. Based on these observations, we conclude that water is a polymeric poor solvent for polyglutamine. Previous studies have shown that monomeric polyglutamine is intrinsically disordered. These observations combined with our fluorescence correlation spectroscopy data suggest that the ensemble for monomeric polyglutamine is made up of a heterogeneous collection of collapsed structures. This result is striking because the preference for collapsed structures arises despite the absence of residues deemed to be hydrophobic in the sequence constructs studied. Working under the assumption that the driving forces for collapse are similar to those for aggregation, we discuss the implications of our results for the thermodynamics and kinetics of polyglutamine aggregation, a process that has been implicated in the molecular mechanism of Huntington's disease.

Collapse of stamps for soft lithography due to interfacial adhesion

Collapse of elastomeric elements used for pattern transfer in soft lithography is studied through experimental measurements and theoretical modeling. The objective is to identify the driving force for such collapse. Two potential driving forces, the self-weight of the stamp and the interfacial adhesion, are investigated. An idealized configuration of periodic rectangular grooves and flat punches is considered. Experimental observations demonstrate that groove collapse occurs regardless of whether the gravitational force promotes or suppresses such collapse, indicating that self-weight is not the driving force. On the other hand, model predictions based on the postulation that interfacial adhesion is the driving force exhibit excellent agreement with the experimentally measured collapse behavior. The interfacial adhesion energy is also evaluated by matching an adhesion parameter in the model with the experimental data.

Drying-induced hydrophobic polymer collapse.

We have used computer simulation to study the collapse of a hydrophobic chain in water. We find that the mechanism of collapse is much like that of a first-order phase transition. The evaporation of water in the vicinity of the polymer provides the driving force for collapse, and the rate limiting step is the nucleation of a sufficiently large vapor bubble. The study is made possible through the application of transition path sampling and a coarse-grained treatment of liquid water. Relevance of our findings to understanding the folding and assembly of proteins is discussed.

Características de frutos de café sob compressão

As condições necessárias para a realização de ensaios de compressão em frutos de café visando à obtenção de resultados confiáveis das forças envolvidas no colapso do produto, foram investigadas neste trabalho e determinados os requerimentos de forças, deformações e energias para o colapso do material sob compressão. As variáveis independentes investigadas foram: presença do pedúnculo no fruto, velocidade de compressão, grau de maturação dos frutos e posição do produto durante a compressão. Os frutos testados encontravam-se em três estádios de maturação: 'cereja', 'verdoengo' e 'verde'. As análises dos resultados mostraram que, para se ter um erro menor ou igual a 10% na estimativa das forças de colapso do produto, são necessárias amostras de, pelo menos, cinqüenta frutos. Os valores das forças, deformações específicas e energias, para o colapso de frutos 'cereja', não foram afetados pela presença do pedúnculo no produto. A velocidade de compressão parece não influenciar nos valores das grandezas investigadas; já a posição do produto, ao ser comprimido, e o estádio de maturação do fruto, mostraram ser variáveis significativas.

Car size and injury risk: a model for injury risk in frontal collisions

Empirical studies have established that when pairs of similar cars collide, the relative injury risk between pairs of different size is inversely related to their mass ratio. Further empirical studies have shown that in frontal collisions between dissimilar cars, relative injury risk is inversely proportional to mass ratio raised to the power of n. The value of the exponent n increases with impact speed, with n≈1 at low speeds and n ranging from 2.81 to 3.74 for fatalities. In this paper a theory is derived which explains relative injury risk in terms of three parameters: length (or size) ratio, mass ratio and the ratio of collision energy absorption between the colliding vehicles. It is proposed that the ratio of collision energy absorption between colliding vehicles is a function of the structural collapse forces imposed at maximum dynamic crush. The theory shows that the fundamental factor in collisions between pairs of similar cars is size, i.e. length. For collisions between two dissimilar cars, Monte-Carlo simulations using generalised characterisations for the car population yield theoretical predictions that match empirical findings ranging from minor injuries (AIS1+) to fatal (AIS6) injuries.

Confined polymer chains in poor solvent

The conformation of polymer chains in a poor solvent and confined in a slit of width D is studied. A variational theory is used to calculate the mean square end-to-end distance. For the asymptotic values of D, the results coincide with the prediction of the scaling theory. For small values of D, the polymer has a two-dimensional ( d=2) behavior, while for large values of D the polymer behaves as a three-dimensional ( d=3) system. The cross-over between these two regimes occurs monotonically. The effect of the interaction strength between the polymer and the plates is assumed to be repulsive ( C 0>0) and shown to be less important than the effect of collapse forces between monomers.

Suppression of Stiction in MEMS

AbstractStiction failures in microelectromechanical systems (MEMS) occur when suspended elastic members are unexpectedly pinned to their substrates. This type of device failure develops both in fabrication and during device operation, being a dominant source of yield loss in MEMS. Stiction failures require first a collapse force that brings the elastic member contact with the substrate followed by an intersolid adhesion sufficiently large to overcome the elastic restoring force. Stiction failure mechanisms have been studied extensively elsewhere [1]. This paper briefly summarizes these mechanisms in a the practical way. Over the last decade, stiction failure rates in MEMS have been minimized using a wide variety of processing, surface treatment, and physical schemes. An update of these methods is provided.

Initiation and propagation of cell collapse in dynamic compression of cellular materials

A one-dimensional model of a cellular material is used to simulate deformation in compression at constant velocity. Each cell has a characteristic load-strain curve with a saddle transition to simulate cell collapse. Different cells may have different collapse forces. A damping term is included in the dynamic equations of motion, which are numerically integrated. Particular attention is given to the initiation of collapse and to its propagation, either to adjacent cells (band propagation) or in a random fashion. The actual behaviour depends on the imposed velocity and on the parameters of the characteristic equations. Low velocities tend to favour random propagation while high velocities originate a band that initiates at the moving end. At intermediate velocities two bands form. Equations are derived for the force for propagation of collapse under quasi-static and dynamic conditions. When there is a weaker element, collapse tends to initiate in it and may propagate to adjacent elements, under an approximately constant force which is affected by damping. When there are large differences among the collapse forces of the various elements, collapse occurs under an increasing load.

The Crushing Mechanics of Bow Structure in Head on Collision (1st Report)

To know the force and displacement in the case of head on collision is quite important in designing safe ship. In this paper, the Yang & Caldwell's technique of deriving simplified equation of mean collapse force based on the Wierzbicki's collapse mechanism is improved and applied to the ship bow structures. The ship bow structure is divided into simple elements of L shape, T shape and + shape. The absorbed plastic energy in crushing of the these elements is derived. The method is extended to the case in which plates of several different thickness exist. The collapse modes are chosen so that the collapse force becomes minimum, while maintaining the consistency between elements. The absorbed energy of each elements are summed up to be the total absorbed energy in the crushing of the bow structure. The number of waves between frames is determined to make the collapse force minimum. The crushing force is computed as the absorbed energy divided by the crushing length. Also extension are made to the non-prismatic structures.The finite element analysis using MSC/DYTRAN is applied to verify the validity of this approach. The comparisons are made with experiments by Nagasawa et al. The good agreements of this simplified equation with numerical analysis and experiments are observed.

Folding kinetics of proteins and copolymers

We model the kinetic processes by which globular proteins and other heteropolymers fold to compact states. We perform Monte Carlo dynamics simulations on short self-avoiding copolymer chains on two-dimensional square lattices. The driving force for collapse is the aversion of nonpolar monomers for water. The chain monomers are of two types, H and P; favorable interactions occur among HH contacts. One respect in which this study differs from previous Monte Carlo folding studies is that the chains are sufficiently short that: (i) we can know unequivocally which conformations are at global minima (the ‘‘native’’ states) and which are at local minima of free energy, (ii) we can explore ‘‘pathway space’’ densely to determine the relative probabilities of all the possible pathways, and thus we establish that the model is ergodic and gives the equilibrium distribution in the long-time limit. We find that any individual molecule passes through a wide range of conformational states, often many times. Nevertheless, this meandering is not inconsistent with the observation that proteins fold through specific pathways involving particular sequences of events. Some pathways are strongly favored; i.e., folding is ‘‘cooperative’’ in that a ‘‘nucleating’’ HH contact acts as a constraint that restricts local conformational freedom and speeds the ‘‘zipping up’’ of other contacts nearby. Which pathways are favored depends on the sequence and the solvent. How does a chain fold to its native state so quickly? For these short chains of fixed length, we observe three regimes of folding kinetics. In the ‘‘Levinthal limit,’’ as the HH attraction approaches zero, folding is slow because the molecule searches randomly through the large ensemble of open conformations. In the ‘‘multiple minima’’ limit, when the HH attraction is very strong, folding is also slow because the chain becomes stuck in local minima of wrong compact conformations. However, we find that folding is relatively fast for intermediate HH attraction because the driving force ‘‘directs’’ the molecule toward a small ensemble of compact states, and yet incorrect potential wells are not too deep to slow this process.

Dynamic modes of plastic deformation for suddenly loaded, curved beams

A curved rigid-plastic structure that is loaded by a suddenly applied force deforms in a modal configuration with rigid segments connected by ‘plastic hinges’. The mode depends on both the structural configuration and the force. When the applied force F exceeds the static collapse force for a curved structure, tangential resultant forces at plastic hinges can cause the number of modal segments to be a function of F. Displacement constraints that make the tangential force increase with the applied force result in an indefinitely large number of segments for the mode during impulsive loading.

The limit of mass for gravitational collapse and nuclear forces at short distance

On the basis of the current knowledge about the size of the neutron, the nucleon-nucleon interaction, and the limit on the ratioGm/c 2 R<4/9 imposed by General Relativity, we find an upper limit of about 2M⊙, for stars of uniform density in the neutron phase. The importance of an accurate determination of the neutron radius for neutron stars studies is pointed out.

The collapse of helium platelets in molybdenum

Platelets of helium in molybdenum have been observed to collapse into several small helium bubbles rather than into a single bubble [10]. We show that the driving force for collapse into n bubbles increases as n decreases. However, kinetic factors associated with the nucleation of ledges on the flat faces of the platelets ensure that the frequency of nucleation of several small bubbles far exceeds that for a single bubble. The temperature at which this collapse is expected correlates well with the observed platelet behaviour.

THE PARTICLE STATISTICS OF RUBBLE PRODUCED BY UNDERGROUND NUCLEAR EXPLOSIONS

Underground nuclear explosions produce cavities into which the overburden may collapse, forming a rubble‐filled chimney. The particle statistics, especially mean surface‐volume diameter, are important to various potential applications of nuclear explosives. The available rubble statistics are rather limited, even with the best data obtained from post‐shot exploration of the Hardhat event. Two sets of Hardhat data are presented: one based on photographs of relatively undisturbed rubble, and another obtained from visual estimates of what would be obtained by screening. The method of obtaining particle statistics must be consistent with the intended use of the statistics, because the method of measurement, such as handling for sieving, affects the statistics. It has long been established that crushing and grinding (which occur during chimney collapse) force particle statistics toward the lognormal frequency distribution. Both sets of Hardhat data fit the lognormal distribution in a satisfactory manner. The volume‐surface mean particle diameter for the undisturbed Hardhat rubble is 1.33 ft, and the estimate for the volume‐surface mean particle diameter obtained by screening is 0.433 ft. Additional statistics from the field plus a better understanding of rock‐fracture phenomena are required to develop statistical relations for use in prediction and control of underground nuclear explosion effects.

The Electrochemical Approach To Cavitation Damage and Its Prevention

Abstract This paper presents a unified theory on the interrelationship between electrochemical and mechanical factors causing damage to materials subjected to cavitating environments. The ambiguous term “cavitation erosion” is rejected in favor of three modes ot damage which depend on the severity of cavitation collapse forces: Cavitation Deformation or Fracture; Cavitation Fatigue; and Cavitation Corrosion. The authors describe some model propeller experiments which demonstrate Cavitation Fatigue damage and how specific cathodic protection measures reduce the damage. An extensive bibliography is appended. 3.5.3

Electronic brains “shrinking”

In this study, energy absorption characteristics of aluminum nested three-tube structures as one of the types of thin-wall energy absorbers were experimentally and numerically examined and some optimal conditions were presented for such structures. In so doing, after determining the type of alloy and stress-strain curves of the tubes, four samples were analyzed under quasi-static collapse. The structures were simulated using finite element software LS-Dyna and the results were compared with data from experimental tests. There was good agreement between experimental and numerical results. After comparing multi-tubular structures with single conventional structures, it was indicated that these structures have a higher capacity to absorb energy. Then, with considering different height and thickness for the structures, the optimal value of these quantities was determined and it was shown that through optimizing three-tube structures, the maximum collapse force can be as low as possible and energy absorption capacity can be hold high. Finally, by optimizing the results with response surface method using Minitab software, samples with optimal performance in the process of collapse were obtained.