Helical fracture in cylinders

Helical fracture in long cylinders is caused by the selfradiation of the moving crack. The pitch of the fracture helix gives information about the crack speed and the ductility of the rupture process.     

Compression fracture statistics of compacted cement cylinders

A statistical analysis of the compression fracture stress of compacted cement paste cylinders was made by comparison of normal, logarithmic normal and Weibull distributions. The influence of specimen size on the fracture stress was determined and compared with predictions based on crack propagation results. The results of the analysis show that the Weibull modified statistics fit in very well with the behaviour observed.     

Structural integrity assurance of high-strength steel gas cylinders using fracture mechanics

This paper describes fracture mechanics criteria employed in the development of fracture-safe, 155–175 ksi strength level steel cylinders. A new steel composition was developed to obtain the toughness required to satisfy leak-before-break and plastic fracture mode criteria. Cylinders were fabricated from the new steel, and tests were conducted to characterize their flaw tolerance capability. Leak-before-break and plastic fracture mode performance was verified. Flawed cylinder tests were also conducted on conventional 3AA 4130X steel cylinders (105–125 ksi strength level) to characterize their flaw tolerance capability. The flaw tolerance capability of the high-strength cylinders was found to be equal to that of the conventional low strength steel cylinders at respective service stresses.     

Fatigue and fracture characteristics of aluminum alloy cylinders under internal pressure

This paper presents the results of tensile, plane-strain fracture-toughness, and fatigue evaluations of die forged and premium cast hydraulic cylinders of six high strength aluminum alloys. Comparisons are made of fatigue strengths at stress levels related to design values, and of relations between values of K_Ic and the conditions under which unstable crack growth was observed in the fatigue tests.     

Investigation of the fracture and fragmentation of explosively driven rings and cylinders

Cylinders and rings fabricated from AerMet^® 100 alloy and AISI 1018 steel have been explosively driven to fragmentation in order to determine the fracture strains for these materials under plane-strain and uniaxial-stress conditions. The phenomena associated with the dynamic expansion and subsequent break up of the cylinders are monitored with high-speed diagnostics. In addition, complementary experiments are performed in which fragments from the explosively driven cylinders are recovered and analyzed to determine the statistical distribution associated with the fragmentation process as well as to determine failure mechanisms. The data are used to determine relevant coefficients for the Hancock–McKenzie (Johnson–Cook) fracture model. Metallurgical analysis of the fragments provides information on damage and failure mechanisms.     

Effects of yielding and size upon fracture of plates and pressure cylinders

The investigation on the yielding at crack tips, its implication on fracture, size effect and its relation to the Griffith criterion of fracture and to the failure of pressure cylinders, and finally the correlation of fracture of plates with that of cylinders are presented herein.By means of the formula derived for the yielding zones at crack ends, it is shown that for failure besides the fulfilment of the Griffith condition, the yielding zones should attain critical dimensions and that in cylinders of all material and in flat plates of high strength material the width of the yielding zone is the same for a given size over a wide range of stresses.The size effect for plates of high strength material is expressed by a formula relating the Griffith stress to the applied stress, critical crack length and the width of specimen: but in the case of more ductile material different formula is derived on the basis that in different sizes of plates the yielding zones have the same width for crack lengths proportional to the width of specimens. The size effect obtained for cylinders not only yields the solution for failure mechanism of cylinders but furnishes the means of obtaining the rate of strain energy release when the formula is applied to test results.Finally a correlation between the fracture of flat plates and that of pressure cylinders on the basis of strain energy release is established. By means of this correlation and with the formula for failure of cylinders the computing of failing stresses for cylinders of different radii is made possible.The test data used to substantiate theory consists of four materials. They are two aluminum alloys, stainless steel and a titanium alloy. The width of flat plate specimens in tests is in the range from 2.25 in. to 30 in. and the radii of cylinders are from 3.6 in. to 15 in.

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Zusammenfassung Dieser Bericht handelt über eine Untersuchung des plastischen Fließens an den Extremitäten einer Einkerbung, sein Einfluß auf das Bruchverhalten, über Größeneinflüsse und ihre Zusammenhänge mit dem Kennwert von Griffith, dem Bruch von Druckzylindern Bowie über den Bruch von Blechen und von zylindrischen Hüllen.Mit Hilfe von zur Bescreibung des Fließverhaltens an den Rißrändern abgeleiteten Formeln wird gezeigt, daß die plastischen Bereiche sowohl die Griffith-bedingungen erfullen als auch kritische Abmessungen annehmen müssen. Außerdem wird bewiesen, daß in Zylindern aus beliebigen Werkstoffen und in Blechen aus hochfestem Material für gegebene Abmessungen, die Breite der plastischen Zone über einen weiten Bereich von Spannungen die Gleiche bleibt.Im Falle von Stahlblechen wird der Größeneffekt durch eine Formel beschrieben, welche das Verhältnis der Griffith-Spannung zur angelegten Spannung, die kritische Rißlänge Bowie die Breite des Probenstabes in Betracht zieht. Im Falle von duktileren Werkstoffen hingegen ergibt sich eine andere Formulierung welche begründet ist auf der Similität der Breite der plastischen Zonen für verschiedene Blechabmessungen wenn die Rißlängen der Breite der Probenstäbe proportional sind. Der für Zylinder erhaltene Größeneffekt gibt nicht nut Auskunft über den Bruchmechanismus, sondern ermöglicht es außerdem das Ausmaß der Freisetzung von Verformungsenergie zu bestimmen wenn man die Formel auf Versuchsergebnisse anwendet.Zum Schluß wurde, auf Grund der freigesetzten Verformungsenergie, eine Korrelation zwischen den Bruchbedingungen an flachen Blechen und denjenigen an Zylindern aufgestellt.Dank dieser Korrelation und unter Anwendung der Bruchformel für Zylinder ist es möglich die Bruchspannung für Zylinder verschiedener Abmessungen zu berechnen.Die Versuchsergebnisse; welche es ermöglichten these Theorie zu prüfen, beziehen sich auf vier Werkstoffe: zwei Aluminiumlegierungen, em rostfreier Stahl und eine Titanlegierung. Die Breite der Flachproben lag zwischen 2,25 und 30 Zoll und die Halbmesser der Zylinder zwischen 3,6 and 15 Zoll.

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Résumé Le mémoire est relatif à une étude de l'écoulement plastique aux extrémités d'une entaille, à ses implications sur la rupture, aux effets dimensionnels et à leurs relations avec le critère de rupture de Griffith et avec la rupture de cylindres de pression et finalement, aux corrélations entre la rupture de tô1es et celles de corps cylindriques.En recourant aux formules décrivant les zones d'écoulement plastique aux extrémités d'une fissure, on démontre que les zones plastiques doivent atteindre une dimension critique, outre la nécessité de remplir la condition de Griffith. On démontre aussi que daps les cylindres en matériau quelconque et dans les tôles planes en matériau à haute résistance, la largeur de la zone plastique est la même pour une dimension donnée, sur une large gamme de contraintes.L'effet dimensionnel dans le cas des tôles en acier à haute resistance s'exprime par une formule comportant le rapport de la contrainte de Griffith à la contrainte appliquée, la longueur critique de fissure et la largeur de l'éprouvette. Dans le cas de matériaux plus ductiles, néanmoins, une formulation différente est trouvée, qui se base sur la similitude de largeur des zones plastiques pour différentes dimensions de tôles, lorsque les longueurs des fissures sont proportionnelles à la largeur des éprouvettes. Dans le cas des cylindres, l'effet dimensionnel calculé rend non seulement compte du mécanisme de lent rupture, mais permet en outre d'obtenir le taux de libération d'énergie de déformation si la formule est appliqu6e aux résultats d'essais.Enfin, on a établi une correlation entre les conditions de rupture de tôles planes et celles de cylindres de pression sur la base de la libération d'energie de deformation.Grâce à cette corrélation, et en appliquant la formule de rupture des cylindres, il est possible de calculer les contraintes de ruine pour des cylindres de divers diamètres.Les données expérimentales ayant permis de vérifier la théorie sont relatives à quatre matériaux: deux alliages d'aluminium, un acier inoxydable et un alliage de titane. La largeur des éprouvettes planes était comprise entre 2,25 et 30 pouces et les rayons des cylindres considérés s'échelonnaient entre 3,6 et 15 pouces.

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Some results of this paper were originally presented under the title Fundamentals of Fracture in Metallic Sheets at the Fifth U. S. National Congress of Applied Mechanics, held in Minneapolis, Minnesota, 1966.

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Editorial Note: Through an administrative oversight, this paper, originally accepted for publication two years ago, inadvertently never reached publication. The paper is now published with apologies to the author.     

Dynamic tensile deformation and fracture of metal cylinders at high strain rates

An experimental study has been presented on the radial deformation of aluminium and copper cylinders of internal diameter 52 mm and wall thickness 1–7 mm, internally loaded with high explosives. High speed photography and flash radiography have been employed to record the distance–time (x–t) history of the cylinder wall, which has been found to expand under strain rates of 10⁴–10⁵ s⁻¹. The rupture of the cylinder is identified by the leakage of detonation gases, through the cracks in the cylinder wall. Rupture strains of 70–160% have been found for commercially pure aluminium. For a fixed wall thickness, the rupture strain increases with the strain rate. However, when the cylinder wall thickness is changed, a maximum is observed in a graph showing the strain and strain rate relationship. Aluminium appears to follow the Ivanov rupture criteria. From the experimental data the macroscopic viscosity coefficient for aluminium has been found to be 0.55–0.87×10³ Pa s. In the deformation of a copper cylinder the cracks initiate at strains of 30–60%, followed by rupture at very high strains up to 300%. The crack propagation velocity through the copper cylinder wall has been found to be 250–300 m/s. Recovered fragments show wall thinning by 50–60% and also exhibit shear fracture which dominates the radial fracture in high velocity deformation of the metal cylinder.     

Mechanical and fracture properties of aluminium cylinders manufactured by orbital friction stir welding

Butt welding of AA6063 aluminium cylindrical shells was performed using the orbital friction stir welding (FSW) method. Tool rotation speed and orbital speed (i.e., traverse speed of rotating cylinder during welding) were considered as variable, and the strength and the mechanical properties including tensile strength, microhardness, mode I fracture energy and mode I crack growth behaviour of manufactured cylinders were investigated experimentally. A novel and subsized test specimen was designed and manufactured for fracture testing of specimens extracted from both base metal and weld zone region of cylinders. The initial precrack was introduced along (i) the tool penetration through the pipe thickness (i.e., T‐direction) and (ii) along the tool travelling direction (i.e., L‐direction). It was found that the crack growth resistance and fracture energy values of FSW samples are greater than the corresponding values of base aluminium material along both “L”‐ and “T”‐directions. Also, the fracture resistance value in T‐direction was higher than the L‐direction for the whole tested FSW samples with different welding speeds.     

Estimations of creep fracture mechanics parameters for through-thickness cracked cylinders and finite element validation

This paper compares engineering estimation schemes of C* and creep crack opening displacement (COD) for cylinders with circumferential and axial through‐thickness cracks at elevated temperatures with detailed 3D elastic‐creep finite element results. Engineering estimation schemes include the GE/EPRI method; the reference stress (RS) method where the reference stress is defined based on the plastic limit load; and the enhanced reference stress (ERS) method where the reference stress is defined based on the optimised reference load, recently proposed by the authors. Systematic investigations are made not only on the effect of creep‐deformation behaviour on C* and creep COD, but also on effects of the crack location, the cylinder geometry, the crack length and the loading mode. Comparison of the finite element (FE) results with engineering estimations provides that for idealised power law creep, estimated C* and COD rate results from the GE/EPRI method agree best with FE results, suggesting that published plastic influence functions for plastic J and COD for through‐thickness cracked cylinders are reliable. For general creep‐deformation laws where either primary or tertiary creep is important and thus the GE/EPRI method is hard to apply, on the other hand, the ERS method provides more accurate and robust estimations for C* and COD rate than the reference stress method. As these two methods differ only in the definition of the reference stress, the ERS method maintains benefits of the reference stress method in terms of simplicity, but improves accuracy of the estimated J, C* and COD results.     

Probabilistic strength of glass cylinders subjected to flexure: total and local probabilities of fracture

The parameters of the specific-risk-of-fracture function of Weibull were determined for glass cylinders subjected to flexure. The total probability of fracture was used considering the maximum stress of fracture, and considering also the location of fracture. Weibull's parameter m obtained by means of both procedures is in keeping with theory and it amounts to m = 7.5. In addition, the dispersion of Weibull's parameters was studied using the inversion of Fisher's information matrix, whose values showed a correct execution of testing. Moreover, the distribution of fracture time during testing was investigated, and neither fracture stresses nor location thereof exhibited whatever influence attributable to this time.     

一种平板状爆炸焊接用炸药

将硝酸铵、硝酸钠、尿素、水、机油和Span80等通过乳化技术制备出乳胶基质。将制备好的乳胶基质和泡沫树脂混合,得到一种平板状炸药。实验表明:该种炸药的密度可低至0.17g/cm³,爆轰的临界厚度为18 mm,在最低临界密度下的爆速为1 678 m/s;随着密度的增加,爆速增加。密度为0.23 g/cm³时,测得爆速为2 149 m/s。初步分析,该炸药可满足某些爆炸焊接工艺的要求。     

粉状乳化炸药爆炸特性的实验研究

文章研究了粉状乳化炸药的爆炸特性－最大爆炸压力（Ｐｍａｘ）和最大爆炸压力上升速率［（ｄＰ／ｄｔ）ｍａｘ］，考查了各种因素对爆炸特性的影响，并与玉米粉和ＴＮＴ的爆炸行为进行了对比。试验结果表明，粉状乳化炸药与ＴＮＴ相比有着低得多的最大爆炸压力和最大爆炸压力上升速率。从火焰传播机理看，粉状乳化炸药更象非自供氧的玉米粉尘。     

铝合金-钢爆炸焊接装药量与界面性能的关系(英文)

通过设计不同的爆炸焊接工艺参数爆炸复合了铝合金-钢爆炸复合板,并对复合板的界面性能进行了显微分析和力学性能测试,探讨了爆炸焊接装药量对复合板界面性能的影响。结果表明:在铝合金-钢复合板的的结合界面产生了一层金属间化合物并且在化合物中产生了许多微裂纹。随着装药量的增加,界面化合物的厚度略有增加,其上微裂纹的的数量也有所增加。复合界面的剪切强度随着装药量的增加而有所降低。界面化合物对复合板强度产生不利影响,铝合金-钢爆炸焊接时应尽量采用小药量。     

Effects of T-stresses on fracture initiation for a closed crack in compression with frictional crack faces

This paper studies crack extension resulting from a closed crack in compression. The crack-tip field of such a crack contains a singular field relative to K _II and non-singular T-stresses T _x and T _y parallel and perpendicular to the crack plane, respectively. Using a modified maximum tensile stress criterion with the singular and non-singular terms, the kinking angle at the onset of crack growth is determined by a two parameter field involving the mode-II stress intensity factors and T-stresses, and at fracture initiation a wing crack may be created at an arbitrary angle from 0° to 90°. A compressive T _y increases the kinking angle and reinforces apparent mode-II fracture toughness, while a compressive T _x decreases the kinking angle and enhances apparent mode-II fracture toughness. The direction and resistance of fracture onset is strongly affected by T-stresses as well as frictional stress. The von Mises effective stress is determined for small-scale yielding near the crack tip. The effective stress contour shape exhibits a marked asymmetrical behavior unless 2T _x  = T _y  ≤ 0 for plane stress state. Coulomb friction between two crack faces generally increases the kinking angle, shrinks the size enclosed by the effective stress contour and enhances apparent fracture toughness. Field evidence and experimental observations of many phenomena involving the growth of closed cracks in compression agree well with theoretical predictions of the present model.     

爆炸焊接布药工艺与微观结合界面形貌分析

爆炸焊接是复合材料加工的1项高新技术,不同的爆炸焊接布药工艺对复合板的质量有很大影响。通过对传统的均匀布药工艺和新不等厚度布药工艺进行爆炸焊接试验和理论分析,发现传统的均匀布药工艺所得到的焊接大波状结合界面明显、复合板质量不好,而新不等厚度布药新工艺可以使炸药产生的爆轰压力逐渐减少,并和材料本身振动产生的惯性力协调作用,得到基本一致的微小波状结合界面,同时降低震动和噪声。结论表明新工艺对工业生产和爆炸焊接试验有很好的指导作用。     

浅谈MRB乳化炸药废料处理

文章叙述了MRB型乳化炸药废料的分离、分析及处理方法。研究发现，利用间断式生产线与立式胶体磨可很好地处理MRB型乳化炸药废料，具有较好的社会效益和经济效益。     

Elastic contact of two cylinders

We study the axially-symmetric problem of contact of two long elastic cylinders one of which is placed into the other under the action of a load varying along the axis. It is shown that if the loaded area is small as compared to the length of the cylinders, then there exist regions of separation, which should be taken into account. The comparison of solutions obtained by taking into account and by neglecting these regions demonstrates that they indeed can be neglected in computing contact stresses (with accuracy sufficient for practical purposes). In addition, we pose and solve a problem of contact interaction of a long elastic cylindrical band with a cylinder placed inside it. For this system, we study the cases of fixed and unknown contact area. Franko L'viv State University, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 3, pp. 31–38, May–June, 1997.