Fracture development in solid perspex spheres with short cylindrical projections (bosses) due to point explosive loading

Fracture and void development in Perspex spheres with bosses (i.e. with cylindrical projections) due to point explosive loading by a detonator have been examined using high speed photography. The order in time, at which cracks or voids occur and their respective locations is discussed by reference to ray reflection from the free boundary. The different natures of the voids created is shown and an explanation of resulting terminal fracture patterns is offered.     

A note on fracture and deformation in cubical box structures due to impulsive loading

The purpose of the investigation was to examine and contrast the patterns of fracture and deformation of cubical box-like structures open on one side, when impulsively loaded. Part 1: Brittle cubical boxes of plaster of Paris, open on one side, were subjected to intense impulsive point loading. The resulting terminal fracture patterns are shown and discussed. Part 2: A small number of thin metal boxes were point loaded by the impact of a heavy slow moving mass. The resulting plastic deformation patterns are described and discussed. In the Appendix, energy absorption due to bending is estimated and related to the results of Part 2.     

Fracture in solid spheres and circular disks due to a “point” explosive impulse on the surface

The results of an experimental study of the fracture of solid spheres and circular disks due to the explosion of a detonator on the surface are presented and a simple analysis is developed which reasonably explains the nature of the characteristic fracture patterns encountered.     

A note on deteriorating jobs and learning effects on a single-machine scheduling with past-sequence-dependent setup times

A result in a recent paper by Yin et al. (Int J Adv Manuf Technol 46:707–714, (2010) is incorrect because job processing times are variable due to both deteriorating jobs and learning effects, a consideration which was not taken into account by the authors. In this note, we show by a counter-example that the published result is incorrect.     

Effect of geometry change of rough point contact due to lubricated sliding wear on lubrication

The geometry change of a single asperity due to lubricated wear was studied by an experimental simulation with a ball‐on‐disc set up. The wear leads to the formation of a tilted section at the tip of the ball, which is proved to be due to the presence of oil during the process. The effect of the geometry change of rough surface contacts due to wear was examined by a micro‐EHL analysis. A non‐Newtonian visco‐plastic fluid model which includes the effect of a limiting shear strength was used. This revised version was published online in June 2006 with corrections to the Cover Date.     

Investigation of the effect of cutting tool edge radius on material separation due to ductile fracture in machining

This paper investigates the interaction between cutting tool edge radius and material separation due to ductile fracture based on Atkins’ model of machining. Atkins’ machining model considers the energy needed for material separation in addition to energies required for shearing at the primary shear zone and friction at the secondary shear zone. However, the effect of cutting tool edge radius, which becomes significant at microcutting conditions, was omitted. In this study, the effect of cutting tool edge radius is included in the model and its influence on material separation is investigated. A modification to the solution methodology of Atkins’ machining model is proposed and it is shown that the shear yield stress and the fracture toughness of the work material can be calculated as a function of uncut chip thickness.     

角接触球轴承外沟位置测量压点移位对测量误差的影响

通过对角接触球轴承外沟位置测量误差的分析,在磨加工过程中对测量误差加以调整,有利于提高双联、多联轴承的配对率和万能组配的合格率。     

A fracture movement monitoring system to aid in the assessment of fracture healing in humans

This paper presents a new design for a device to monitor the motion of fracture fragments in diaphyseal tibial fractures. The device measures the motion that occurs at the fracture site when loaded by gait or by manipulation. It has undergone rigorous calibration and acceptance trials. The device has been used in ethically approved research clinics held at the North Staffordshire Hospital (40 patients). The paper presents a selection of results obtained using the new device. The results demonstrate several new ways of assessing fracture healing by examining fracture site motion. The following conclusions were drawn: 1. If fracture monitoring devices are to be attached to bone screws, it is essential to minimize bone screw errors. To do this, each patient must have similar bone screw lengths, orientations, alignment and siting. This is only achievable using a peroperative reduction device. 2. If fracture stiffness is to be used as a measure of fracture healing, load rate should be controlled; at the very least strain rate should be controlled. 3. It is imperative that fracture stiffness be measured in more than one plane by a biplanar device so that asymmetry may be accommodated. 4. Fracture stiffness, on its own, is probably not a sufficiently rigorous measure of healing end-point. The quantifiably viscoelastic properties of healing callus should be taken into account.     

A note on productivity gains in flexible robotic cells

Flexible robotic cells combine the capabilities of robotic flow shops with those of flexible manufacturing systems. In an m-machine flexible cell, each part visits each machine in the same order. However, the m operations can be performed in any order, and each machine can be configured to perform any operation. We derive the maximum percentage increase in throughput that can be achieved by changing the assignment of operations to machines and then keeping that assignment constant throughout a lot's processing. We find that no increase can be gained in two-machine cells, and that the gain in three- and four-machine cells each is at most 14 %.     

Field investigation of variation of loading pattern of concrete sleeper due to ballast sandy contamination in sandy desert areas

Sleeper is one of the most important components in a railway track system. Thus, for accurate analysis and design of concrete sleepers, knowledge of imposed loading pattern is necessary. Sandy desert areas are critical regions where loading status of concrete sleeper is different from other areas. In these areas, the influence of flowing sand grains between the ballast aggregates increase the stiffness of ballast layer; consequently, rail support modulus increases, so the received share of total axle load subsequently increases on the sleeper which is placed under the wheel load. On the other hand, the pressure distribution underneath the sleeper changes considerably. In this paper, the results of a field investigation about the variation of rail support modulus and also variation of loading pattern of concrete sleeper followed by the variation of bending moment of sleepers in sandy desert regions were presented.     

Measurement of pressures in the nucleus and within the annulus of the human spinal disc: due to extreme loading

Specially developed intervertebral and intradiscal pressure transducers are used to map the pressures in the nucleus pulposus and within the annulus fibrosus of the human spinal discs, to the point of fracture of the segmental units. The results show that for normal discs, pressures in the nucleus and in the annulus are linearly related to each other and to the applied compressive loads. Mechanical strains which develop around the periphery of the vertebral body are also linear with the applied compressive loads, when the partial vertebral column is loaded to the point of bony fracture. Failure of the intervertebral discs at the point of fracture occurred through the vertebral body endplates and the annulus fibrosus remained intact.     

A study on mild-to-severe wear transition due to inconformity of wear-induced shape

The mechanism of transition in wear-induced, time-dependent mild-to-severe wear was mainly discussed based on the calculation results of simulated wear. Convex-shaped sliding pairs generally accompany the rolling-sliding motion that causes some parts of the sliding surface to again come into contact with different areas of the mated surface as wear proceeds, thus resulting in inconformity of wear shape. The greater the degree of wear shape inconformity, the higher the contact pressure that leads to changes in wear. Some methods of avoiding this kind of wear transition were also discussed.     

A heuristic algorithm to batching and loading problems in a flexible manufacturing system

Part type selection and machine loading are two major problems in the production planning of flexible manufacturing systems (FMS). The two problems are viewed as selecting subsets from the jobs of part types in a planning horizon and allocating jobs of the subsets among machines. In this paper, in order to develop a practical and efficient approach to solving FMS production planning problems, a heuristic algorithm is suggested that develops heuristic rules with the objective of minimisation of the number of tool changes and minimisation of the imbalance in per machine. To compare the proposed algorithm, a series of computational experiments is done on randomly generated test problems and the results show that the developed algorithm is very simple and efficient.     

A heuristic approach to minimize expected makespan in open shops subject to stochastic processing times and failures

Many real world situations exist where job scheduling is required. This is the case of some entities, machines, or workers who have to execute certain jobs as soon as possible. Frequently what happens is that several workers or machines are not available to perform their activities during some time periods, due to different circumstances. This paper deals with these situations, and considers stochastic scheduling models to study these problems. When scheduling models are used in practice, they have to take into account that some machines may not be working. That temporal lack of machine availability is known as breakdowns, which happen randomly at any time. The times required to repair those machines are also random variables. The jobs have operations with stochastic processing times, their own release times, and there is no precedence between them. Each job is divided into operations and each operation is performed on the corresponding specialized machine. In addition, in the problems considered, the order in which the operations of each job are done is irrelevant. We develop a heuristic approach to solve these stochastic open-shop scheduling problems where random machine breakdowns can happen. The proposed approach is general and it does not depend on the distribution types of the considered random input data. It provides solutions to minimize the expected makespan. Computational experiences are also reported. The results show that the proposed approach gives a solid performance, finding suitable solutions with short CPU times.     

A note on a strain-etching method of revealing the bounding slip-lines to metal-cutting flow zones

The shapes of the entrance and exit slip-lines to the plastic flow zones in a metal-cutting process are obtained by strain etching the polished section of a partly formed chip, which was produced in an incremental cutting operation.The results are compared with the slip-line field solutions of Kudo, for cutting with chip curl. The shapes of the exit boundaries to the primary and secondary flow zones, which are situated in approximately non-hardening metal, show good general agreement with Kudo's perfect plasticity model.     

A study on penetration fracture characteristics of glass plates subjected to impact loadings

In this study, a comparison between theoretical solutions and experimental results are examined for fracture conditions in the case of float glass plates subject to static loadings. The ranges from fracture-generated initiations to critical penetration energies are confirmed according to the impactor mass under high velocity, and an analytical method is presented to determine the fracture strength and penetration strength. Also, fracture patterns are investigated according to impact velocities.     

A note on spherical structures in chars from vitrinites of coking rank

Spherulitic aromatic structures with relatively simple optical characters that form as a transitional phase in the development of mosaic textures are well known in pitch fractions and certain polymers when carbonized. Their occurrence in coal macerals that soften prior to the formation of a mosaic is less certain. Other spherulitic structures, much larger in size than mesophase spherules, can, however, develop from vitrinites with a high potential fluidity under certain carbonization conditions, when fast heating rates are employed. These bodies, besides displaying optical characters that indicate structural symmetry, also show mosaic textures.