Secondary Plastic Research Articles

Elastic-plastic fields near crack tip growing step-by-step in a perfectly plastic solid

In this paper, based on the three-dimensional flow theory of plasticity, the fundametal equations for plane strain problem of elastic-perfectly plastic solids are presented. By using these equations the elastic-plastic fields near the crack tip growing step-by-step in an elastic incompressible-perfectly plastic solid are analysed. The first order asymptotic solutions for the stress field and velocity fields near the crack tip are obtained. The solutions show the evolution process of elastic unloading domain and the development process of central fan domain and reveal the possibility of the presence of the secondary plastic domain. The second order asymptotic solution for stress field is also presented.

Fabrication of microstructures with high aspect ratios and great structural heights by synchrotron radiation lithography, galvanoforming, and plastic moulding (LIGA process)

Under the LIGA process for fabricating microstructures having high aspect ratios and great structural heights, synchrotron radiation lithography produces a primary template which is filled with a metal by electrodeposition. The metallic structure so produced is used as a mould insert for fabricating secondary plastic templates which, in mass production, replace the primary template. This is a report about the status of work performed by the Karlsruhe Nuclear Research Center with the cooperation of Siemens AG and the Fraunhofer Institute for Solid State Technology: By irradiation and development of polymethyl methacrylate (PMMA) plates, primary templates were produced which, for structural heights of several hundred μm, exhibit deviations in critical dimensions of less then some 0.1 μm. The best results were obtained with an X-ray mask consisting of a 25 μm thick beryllium foil and 18 μm thick absorber structures consisting of copper and gold. Practically perfect metallic replicas were obtained by electrodeposition of nickel in the PMMA microstructures and even details in structure of less than 0.1 μm size were reproduced. Moulding was done with a methacrylate-based casting resin with an internal mould release agent. By electrodeposition of nickel in the secondary templates, secondary metal structures were produced which practically do not differ from the primary structures. The LIGA process can be expected to be superior to other methods for fabricating microstructures with high aspect ratios if, in series production of microstructures with complex shapes, stringent requirements are imposed on the resolution, the aspect ratio, the structural height, and the parallelism of the structural walls.

唇・顎・口蓋裂患者の治療例

In orthodontic treatment, patients with cleft lip and/or palate have the following difficulties as compared with non-cleft patients. 1. Anterior and posterior cross-bite due to collapse of the maxillary arch. 2. Poor growth of the maxilla. 3. Strain of the upper lip after surgical treatment. 4. Congenitally missing teeth, supernumerary teeth and transversion, etc.. Therefore, we examined two cases with unilateral cleft lip and palate and one case with bilateral cleft lip and palate who received orthodontic treatment at Kyushu Dental College Hospital. In all cases edgewise technique was used at final step of orthodontic treatment. These cases needed the lateral and antero-posterior expansion of the maxillary arch, the aesthetic and functional recovery by restoration for missing teeth, the permanent fixation against relapse or the secondary plastic surgery of the upper lip and nose.

STRESS DISTRIBUTION IN AN ELASTIC PLASTIC DISK SUBJECTED TO A CIRCULAR HEAT SOURCE

Abstract Stress distribution in a perfectly plastic disk caused by a circular heat source of constant output is investigated. It is shown that, dependent on the ratio of the radius of the disk to the radius of the heat source, Tresca's yield condition assumes different forms. In certain cases, the plastic zone is composed of two parts associated with different branches of the yield condition. The critical time for avoiding secondary plastic flow is discussed.

Abdominoplasty following gastrointestinal bypass surgery.

An increasing number of postgastrointestinal bypass patients are being referred for secondary plastic surgical procedures. Thirteen patients at this institution have undergone abdominoplasty after surgery for morbid obesity in the past 5 years. The characteristic abdominal deformity includes a draping apron of panniculus frequently associated with previous surgical scars and/or ventral hernia. An abdominoplasty of the low, transverse type with wide undermining is appropriate for most patients. However, vertical or mixed-type abdominoplasties and simple panniculectomies are occasionally indicated owing to residual adiposity and scar location. After bypass surgery, self-image and health-related complaints are markedly improved, but psychological gains can be inhibited by persistent body-contour concerns. Gastrointestinal bypass patients have a high incidence of associated medical problems. Preoperative laboratory evaluations must, therefore, be comprehensive. A variety of early and late complications following gastric and jejunoileal bypass are summarized. In spite of an expected higher complication rate following abdominoplasty, no major complications and three minor complications were discovered in these 13 patients.

転がり接触問題解析の一手法 (第2報)

A theoretical approach is presented to the plane theory of rolling contact with friction. An analysis is given of plastic deformation which affects elastic-plastic and residual stress fields in rolling contact. Some effects are discussed of sress fields due to tangential load. In case of static loads, because of friction the tensile zone of residual stress σχis constructed in the neighbourhood of the rear contact area, and the negative shearing residual stress zone is extended widely than that of positive one. The axial residual stress field σz is affected by the secondary plastic flow due to unloading. When the combined loads ran away the values of residual stresses do not vary because of friction, while the tangential load can be understood that specifies the depth of plastic zone.

On the influence of single and multiple peak overloads on fatigue crack propagation in 7075-T6511 aluminum

The phenomenon of fatigue crack retardation due to variable amplitude loading spectra was studied in 7075-T6511 aluminum alloy. Selected precracked compact tension specimens were subjected to single and multiple peak applications of overload stress intensity values and subsequently cycled at lower stress intensities. Detailed characteristics of the fatigue crack propagation process were measured directly on the fracture surfaces using electron microscopy replicating techniques. The degree of retardation was shown to depend strongly on: 1. A. The relative amplitudes of the peak stress intensity ( ΔK 2 ΔK 1 ) 2. B. The number of stress applications N 2 at the peak stress intensity ( ΔK 2) 3. C. The magnitude of the constant amplitude crack growth rate at the lower stress intensity range ( da dn ) ΔK1 4. D. The number of fatigue cycles N 3 at the lower stress intensity level after the last peak stress is applied. A comparison was made between the experimentally observed magnitude of retardation and that predicted using: (1) a model where the retardation is proportional to the ratio of peak stress plastic zone size to secondary stress plastic zone size and (2) an effective stress intensity model. It appears that no present model can accurately predict many of the complex features of the cycle by cycle crack growth behavior experimentally observed. For example, immediately following the last application of the high stress, the crack growth rate at the lower stress levels was accelerated over the value normally observed at constant amplitude cycling (at that same lower stress level). After a period of several cycles, the retardation increased. This is the previously reported delayed retardation effect. After further cycling the crack growth rate slowly increased to what would normally be observed had the peak stress not been applied.

Corrective plastic surgery of the cleft nose

Summary 15 years' experience allows the author to state that secondary corrective plastic operations on the osseous framework, the septum and the triangular cartilage are always a must by cleft nose patients. The procedures for unilaterally or bilaterally involved nose differ, lateral deviation and asymmetry being the main deformities in the first case, and underdeveloped septum and columella and a widened nasal tip in the second. The author describes techniques which are either entirely his own, or through him modified. Diagrams and clinical cases illustrate and fully explain such techniques.

Hardening of copper and nickel alloys during pre-recrystallization annealing and softening during secondary deformation

1. Secondary deformation of both metals and single- and two-phase alloys hardened as a result of the first deformation and pre-recrystallization annealing (or aging) results in considerable softening. 2. Softening is observed after slight reduction during secondary deformation (1–5%) and it mostly takes the form of a reduction to resistance to small plastic deformations. 3. Secondary plastic deformation after primary deformation in the same direction improves the elastic limit, but does not alter the anisotropy of the latter. A change in the direction of secondary deformation leads to alteration of the anisotropy of the elastic limit by increasing hardness in some directions and softening the alloy in others. 4. Secondary plastic deformation of alloys after primary deformation and pre-recrystallization annealing causes softening in all directions, although to a different degree. The nature of the anisotropy depends on the direction of the secondary deformation with respect to the original direction. 5. The Konobeevskii-Rovenskii effect is based on polygonization during pre-recrystallization annealing and disturbance of the polygonized substructure during secondary deformation. This effect is of a general nature and is natural both in pure metals and alloys; in alloys changes in fine structure are complicated by processes involving redistribution of the component atoms and therefore have a strong effect on the degree of hardening and softening.

The management of facial trauma in infants and children

I N RECENT months we have encountered a large number of infants and children with improperly managed facial wounds. Despite the numerous excellent reports on the management of trauma, facial injuries in infants and children continue often to be treated inadequately, and this circumstance prompts this communication. The physician rendering the initial care has the optimum chance to bring about a satisfactory final result. The initial care of facial injuries and lacerations requires much more time and effort than is generally felt necessary, if a satisfactory final result is to be obtained. Scar tissue developing, both deep and superficial, in the soft tissues and skin makes secondary plastic revision difficult, and the eventual result often is far from gratifying. The conspicuous and disfiguring facial scars which result from inadequate initial surgery may represent a real catastrophe, often with long-lasting mental fixation for the patient. During the early stages of ambulation the child is subject to frequent falls and tumbles. Common sites of trauma are the supraorbital and submental areas and the lips.

Buschke-Loewenstein tumors (giant condylomata acuminata)

A case of giant condylomata acuminata with extensive destruction of penile skin and expansion into one corpus cavernosum is presented. Radical removal of all diseased tissue into normal structures and secondary plastic procedure resulted in cure. Pathology, nomenclature and treatment are discussed.