Principal Fracture Research Articles

Thermal stress fracture of refractory lining components: Part III. Analysis of Fracture

The fracture behavior of refractory components heated from one end is simulated using a twodimensional constant heating rate thermoelastic model and the maximum principal tensile stress fracture criterion. Dimensionless graphical relationships that can be used to predict location of fracture and orientation of cracking are presented. Dimensional analysis and the finite element numerical method are used to develop a general solution for the total strain energy. Based on the premise that extent of crack propagation is directly related to available strain energy at fracture and inversely related to the surface energy per unit area, the solution for total strain energy is used to derive a damage resistance parameter useful for the design and selection of refractory components that accounts for material properties, geometry, and heating and cooling rate. Model predictions of location of fracture, orientation of cracking, and extent of crack propagation are in general agreement with experimental results previously reported in the literature. Limitations of the two-dimensional thermoelastic model are discussed.

Treatment of tibial fractures by reaming and intramedullary nailing.

We treated 112 fractures of the tibia by manipulative reduction, reaming of the medullary canal, and fixation of the fracture fragments with an intramedullary nail. Seventy-six of the fractures were acute, and eight of these were second or third-degree open fractures. The other thirty-six fractures had a non-union, osteotomy for malunion, or failure of other types of treatment. Follow-up of 100 fractures showed union in all but one, which was in a drug abuser who had an amputation due to infection. The main complication was infection, which was successfully treated in six of seven fractures. The method of treatment, employing either closed or open technique and recently making use of interlocking bolts to stabilize one or both principal fracture fragments on the nail, is an excellent one for unstable acute fractures and for secondary procedures in fractures that are not associated with infection. The infection rate was increased with the open surgical technique. The few contraindications to its use are described.

Morphological observations of torsional fractures of the adult tibial shaft.

The present study is an analysis of the radiographic morphology of 250 consecutive clinical torsional fractures of the adult tibial shaft. The site, extent, degree of comminution and orientation of the principal fracture plane were determined, with special attention paid to the initial lateral displacement as an estimate of injury to the interosseous membrane. The predilection site of the torsional fractures was at the junction of the middle and distal thirds of the tibia. An additional moment of axial compression in the causative violence seemed to result in a more distal fracture. The orientation of the principal fracture plane did not occur at random. The centre of the actual spiral component of the fracture line was located in the anterolateral and the vertical element of the fracture in the posteromedial quadrant of the tibial circumference in 78 per cent of cases. A latero-medial orientation of the fracture, approaching the sagittal plane and perpendicular to the interosseous membrane, showed increased frequency of severe initial lateral displacement as compared with postero-anterior fractures, lying in the coronal plane (P less than 0.01). Tibial fractures with intact fibulae were seen only in the young, with a mean age of 25 years for these patients, but no other age-associated fracture characteristics were found.

Composite Failure Surface Analysis

In this work, the features of the fracture surfaces of graphite-epoxy specimens as seen by both optical and scann ing electronic microscope (SEM) are presented. A variety of test conditions were investigated. They are: tension (quasi- static), compression (quasi-static), and tension-tension fatigue. Failure due to delamination was also studied (Mode I-Peel Testing). The sequence of events leading to failure was monitored using an X-ray technique with an opaque additive for image enhancement. After mechanical testing, specimens were sectioned and prepared for microscopic analysis. Two principal fracture surface features were identified: (1) overlapping platelets of epoxy and (2) branched microcrack structures. These fatures could be used to identify the direc tion of failure propagation and, in some cases, distinguish between failure modes.

On the African rift system, theoretical and experimental study

The East African rift system is a product of two separate activities. An ancient process (Precambrian?) resulted in brittle crustal fracture, a deep vertical tensional feature. This defined the principal fracture pattern of the continent. It was initiated by an upward diapiric stress and propagated laterally according to the principles of elastic fracture and bifurcation. Later (Jurassic-Recent) horizontal and vertical multi-stage forces caused tectonic displacements along the ancient fractures and the present rift pattern was derived. As opposed to previous models, the present concept is compatible with many conflicting opinions of previous workers (e.g. indications of tensional versus compressional or vertical forces), and is capable of explaining many moot questions.

Fracture Toughness Phenomena in an Unaged Beta Titanium Alloy

The fracture toughness behavior of a commercial beta titanium alloy, Ti-3Al-8V-6Cr-4Zr-4Mo, has been examined between −196°C and 380°C, The observed tough-brittle transition results from increasing amounts of intergranular and cleavage fracture with decreasing temperature. Crack initiation is associated with particle/matrix interface parting, while cleavage crack propagation at low temperature requires the attainment of a critical stress over a characteristic distance. Micromechanical modeling of the principal fracture event associated with critical stress cleavage crack propagation does appear to accurately predict the magnitude of this distance, although it is limited to initiation controlled cleavage fracture events.

Structure of base in Daldyn-Alakitskiy diamond field

The ancient crystalline base is found to be intricately wrench-faulted, with considerable movement of its blocks up, down, and sideways, along the principal and subsidiary fractures. There is a very good correspondence between the tectonic structure of the base and structures of its sedimentary overburden. A connection between tectonic structure of the base and kimberlitic magmatism is definitely indicated. -- V.P. Sokoloff

STRUCTURAL ANALYSIS OF THE QUEENSWAY FOLDS, OTTAWA, CANADA

The Queensway folds are an anticline–syncline pair in layered limestone and shale of the Ottawa Formation in the Ottawa – St. Lawrence Lowlands. They are parallel, flexural-slip folds with horizontal axes trending northwest, parallel to the surface trace of the Gloucester fault.Five principal fracture subpatterns were recognized in the fold-pair, caused by at least four geometrically distinct stress fields. The principal stress directions at failure for all five subpatterns coincided, moreover, with the three orthogonal fabric axes, and the maximum principal stress was either parallel or perpendicular to the fold axes and to the Gloucester fault.Slickenside striae on bedding and on fractures at an angle to bedding indicate two principal kinematic patterns in the fold-pair; the one arises from motion in the deformation plane as a consequence of the folding and the other from strike-slip motion perpendicular to that plane as a consequence of displacement on the Gloucester fault.Slickensides indicate that each bed was free to move relative to adjacent ones during folding and that the fundamental structural unit in flexural-slip folding is the bed. Model studies support the field data and indicate that the sense and magnitude of interbed slip in any structural position is dependent upon an integral of conditions throughout the fold-pair and that the fundamental fold unit is the anticline–syncline pair.

Structure and Fabric on the Burroughs Glacier, South-East Alaska

AbstractThe Burroughs Glacier, south-east Alaska, is a slow-moving remnant (14×3km.) of a much more extensive glacier. It is now entirely below the firn line; ablation has revealed ice structures and fabric once 300 m. or more below the glacier surface.At the present glacier surface three kinds of ice are identified—foliated ice, coarse-grained border ice and very coarse-grained basal ice.Two systems of fine-grained foliation are present. Differential movement in the glacier has caused recrystallization along closely spaced planes. At the glacier surface this produces a steeply dipping longitudinal foliation. A gently dipping foliation, having a regional trough-like structure, may be associated with former stratification planes or with former spoon-shaped shear surfaces.The optic orientation of crystals in the coarser layers of the foliated ice shows three weak maxima, and in the finer layers a single weak maximum, corresponding to one of the coarse layer maxima, and normal to the gently dipping foliation plane. The other maxima in the coarse layers are orientated close to the poles of principal fracture planes.In the coarse ice the fabric shows a pattern with three maxima similar to that obtained in torsion shear experiments. In the glacier the pattern may be formed by shear near the glacier bottom or along gently dipping foliation planes. Grain-size increases towards the glacier terminus, especially in the stagnant ice zone.Structural evidence suggests that in the early stages of the Little Ice Age the ice flow was from west to east. Later it was to east and west from an ice crest in the upper Burroughs Glacier. Structures produced by present movement have been superimposed on older structures.

Structure and Fabric on the Burroughs Glacier, South-East Alaska

AbstractThe Burroughs Glacier, south-east Alaska, is a slow-moving remnant (14×3km.) of a much more extensive glacier. It is now entirely below the firn line; ablation has revealed ice structures and fabric once 300 m. or more below the glacier surface.At the present glacier surface three kinds of ice are identified—foliated ice, coarse-grained border ice and very coarse-grained basal ice.Two systems of fine-grained foliation are present. Differential movement in the glacier has caused recrystallization along closely spaced planes. At the glacier surface this produces a steeply dipping longitudinal foliation. A gently dipping foliation, having a regional trough-like structure, may be associated with former stratification planes or with former spoon-shaped shear surfaces.The optic orientation of crystals in the coarser layers of the foliated ice shows three weak maxima, and in the finer layers a single weak maximum, corresponding to one of the coarse layer maxima, and normal to the gently dipping foliation plane. The other maxima in the coarse layers are orientated close to the poles of principal fracture planes.In the coarse ice the fabric shows a pattern with three maxima similar to that obtained in torsion shear experiments. In the glacier the pattern may be formed by shear near the glacier bottom or along gently dipping foliation planes. Grain-size increases towards the glacier terminus, especially in the stagnant ice zone.Structural evidence suggests that in the early stages of the Little Ice Age the ice flow was from west to east. Later it was to east and west from an ice crest in the upper Burroughs Glacier. Structures produced by present movement have been superimposed on older structures.