The concept of superposed fracture networks consisting of different generations, and often types, of fractures that have developed sequentially is discussed. Superposed networks can consist of different types of extension or shear fractures, and each fracture may abut, cross or follow (reactivate) earlier fractures. An example of a superposed fracture network in Liassic limestones in Somerset, UK, is presented, which comprises two sets of veins and a later joint network. The veins develop as damage zones around faults, with veins of the later set crossing or trailing along the earlier set. The later joints either cross-cut the earlier veins or reactivate them, the latter being common for the thicker (more than about 5 mm) veins. The veins and joint networks have markedly different geometries and topologies. The veins are spatially clustered and are typically dominated by I-nodes, while the joints are more evenly distributed and tend to be dominated by Y-nodes. The combined network of veins and joints at Lilstock is dominated by X-nodes because so many joints cross-cut the earlier veins. Understanding the development of superposed fracture networks leads to better understanding of the kinematic, mechanical, tectonic and fluid flow history of rocks.

The Niagara Escarpment is a geological feature located in southern Ontario, Canada, and the northeastern United States, comprising highly fractured sandstone, shale and carbonates deposited during the Ordovician and Silurian periods. Differential erosion of the strata has generated a steep cliff face which bisects the city of Hamilton, Ontario. Geological fractures are widespread in the escarpment and result in the formation of unstable blocks of rock subject to erosion through rockfall. This presents structural stability issues of concern due to the proximity of the escarpment to urban infrastructure. We quantify and analyse fracture networks in the escarpment using a combined field- and numerical-modelling-based approach. The location, orientation and aperture of fractures were documented from local outcrops using scanline and area survey methods. Clusters of poles describing the orientation of geological discontinuities were identified in spherical projections, defining three sets: (1) a sub-vertical stratabound set striking N–S, (2) a sub-vertical stratabound set striking E–W, and (3) a set parallel to horizontal sedimentary bedding planes which we infer controlled sub-vertical fracture geometry. Discrete fracture network modelling of fracture sets highlights their high degree of connectivity, and contribution to local geohazards, and quantifies their role in controlling fluid flow through escarpment strata, which is dependent on fracture aperture. Additionally, bedding planes have the potential to act as free surfaces, facilitating stress conditions in which approximately cuboid blocks are produced, and increasing the risk of rockfalls. We conclude that fractures present a first-order control on the fluid-flow properties and stability of the Niagara Escarpment.

This paper presents a method for automatic forming and solving dynamic equations of motion of manipulator with elastic joints and rigid segments. For the minimal configuration of a cylindrical manipulator the numerical integration of these equations is performed, and vibrations in the joints are obtained as dynamic errors with respect to the prescribed trajectory.

This paper presents a complete derivation of the combined flexural-joint stiffness matrix and the elastic deformation field of flexible manipulator arms treated in a three-dimensional fashion. The stiffness properties are derived directly from the differential equations used in the engineering beam theory. The expressions developed here can readily be used in the modeling, control and design of light weight flexible robot manipulators. A two-link arm is used to formulate these expressions and the results can be generalized to n–link manipulators. The stiffness matrix for a robotic link element in 3-D is of the order of 12 X 12, and for an n–link robotic arm the total elemental and system stiffness matrices will be of the order of the (12n X 12n) and 6(n + 1) X 6(n + 1), respectively.

A two-dimensional serial-driven manipulator is compared with two different parallel-driven manipulators, using workspace, power requirements and stiffness as criteria. The parallel-driven devices are based on the planar five-bar linkage; one has four revolute joints and one prismatic joint; the other has five revolute joints. Parallel operation is shown to offer advantages.

The shear failure probabilities of reinforced concrete beam-column joints have been investigated by Monte Carlo method. The theoretical shear strength of joints is based on the softened strut-and-tie model proposed by Hwang and Lee (2002). The random variables included in this study are the strengths of concrete, the ultimate compression strain of concrete, the strengths of reinforcement, the dimensions of cross-section, and the model error of theoretical shear strength of joints. The shear failure probabilities of joints with SD 280 flexural reinforcement in the beams designed using the ACI Code are all higher than 0.04. The joints designed according to the softened strut-and-tie model are safer than those designed according to the ACI Code. The shear failure probabilities of exterior joints are higher than those of interior joints. The shear failure probabilities of joints with SD 280 flexural reinforcement in the beams are higher than those of joints with SD 420 flexural reinforcement.

Les joints de dilatation jouent un rôle important dans les garnissages réfractaires. Ils permettent de diminuer les contraintes durant la montée en température. Il est alors nécessaire de les prendre en compte lors d'un calcul mécanique. Dans le cas où le garnissage est une maçonnerie (composée de briques), il n'est pas possible de modéliser chaque brique et joint. La solution proposée est de remplacer la maçonnerie par un matériau qui aurait le même comportement. Du fait qu'il est difficile de réaliser des essais sur un ensemble de briques (dans le but d'identifier les paramètres du matériau équivalent), ces chargements ont été simulés sur une cellule élémentaire en utilisant un modèle développé à l'échelle des composants, à laquelle les joints sont représentés par un contact. Une identification inverse a permis d'obtenir les paramètres d'un matériau équivalent simplifié qui a été validé à l'aide d'un essai thermomécanique sur une structure réelle.

Ce travail porte sur l'utilisation du verre comme véritable matériau de structure et concerne plus particulièrement le calcul des contraintes résiduelles de trempe autour des zones d'assemblage par insertion d'un connecteur métallique au sein de plaques trouées et chanfreinées pour la prédiction de la résistance de tels assemblages.Des simulations numériques par la méthode des éléments finis du procédé de trempe sont menées pour le calcul des contraintes transitoires et résiduelles près des bords de plaques de verre (calculs 2D) et près de trous chanfreinés (calculs 3D). Le verre est considéré comme un matériau viscoélastique, le modèle de Narayanaswamy est utilisé, il prend en compte les phénomènes de relaxation de contraintes d'origine visqueuse et structurale. Une difficulté provient de la description correcte des transferts de chaleur pendant la trempe qui est d'importance majeure pour la prédiction des contraintes résiduelles. La convection forcée due au soufflage de l'air et le rayonnement sont modélisés, le caractère semi-transparent du verre est pris en compte. Les coefficients de convection forcée dans les zones bords sont identifiés expérimentalement. Les résultats de prédiction des contraintes résiduelles de trempe sont comparés à des résultats de mesures photo-élastiques. Ce travail permet l'optimisation de la géométrie de la plaque de verre pour un renforcement maximal dans la zone d'assemblage.

Routine study of three-dimensional (3D) tarsal kinematics is hampered by errors due to the displacement of skin surface-tracking markers relative to the underlying bones. Reliable kinematics can be obtained with bone-fixed markers, but an accurate, non-invasive method would have more applications. Simultaneous kinematic data from skin-based and bone-fixed markers attached to the tibia and third metatarsus were collected from three trotting subjects. The motion of the skin-based markers was extracted relative to the underlying bone motion tracked using the bone-fixed markers. The 3D skin displacement patterns for the skin-based markers were parameterized using a truncated Fourier series model. These displacements were expressed in terms of the local coordinate system for each bone. Skin displacement artefacts were observed in all three axes of each bone segment, with the largest displacements occurring at the proximal tibia. The mean skin displacement amplitudes in the tibia were 6.7%, 3.2% and 10.5% of segment length, and for the third metatarsus were 2.6%, 1.4% and 3.8% of segment length, for the craniocaudal, mediolateral and longitudinal segment axes, respectively. Skin displacement patterns could be expressed concisely using the Fourier series model. Displacements were also consistent between subjects, which should allow them to be used as a basis for developing a correction procedure for 3D tarsal joint kinematics.

Tectonic joints localized within deformation band shear zones on the Kaibab uplift in Utah, USA, show the same spacing and distribution characteristics as joints controlled by primary lithological mechanical stratigraphy, despite the fact that deformation band shear zones are secondary structural features oblique to primary sedimentary layers. The spacing and distribution of joints that traverse deformation band shear zones are important factors in the permeability and connectivity of sandstone reservoirs compartmentalized by deformation band shear zones.

The fibrillar collagens associated with the articular cartilages, joint capsule and ligamentum teres of the rabbit hip joint were characterised from the 17 d fetus to the 2-y-old adult by immunohistochemical methods. Initially the putative articular cartilage contains types I, III and V collagens, but when cavitation is complete in the 25 d fetus, type II collagen appears. In the 17 d fetus, the cells of the chondrogenous layers express type I collagen mRNA, but not that of type II collagen. Types III and V collagens are present throughout life, particularly pericellularly. Type I collagen is lost. In all respects, the articular cartilage of the hip joint is similar to that of the knee. The joint capsule contains types I, III and V collagens. In the fetus the ligamentum teres contains types I and V collagens and the cells express type I collagen mRNA; type III collagen is confined mainly to its surface and insertions. After birth, the same distribution remains, but there is more type III collagen in the ligament, proper. The attachment to the cartilage of the head of the femur is marked only by fibres of type I collagen traversing the cartilage; the attachment cannot be distinguished in preparations localising types III and V collagens. The attachment to the bone at the lip of the acetabulum is via fibres of types I and V collagens and little type III is present. The ligament is covered by a sheath of types III and V collagens. Type II collagen was not located in any part of the ligamentum teres. The distribution of collagens in the ligamentum teres is similar to that in the collateral ligaments of the knee. Its insertions are unusual because no fibrocartilage was detected.

The mechanics of mammalian intervertebral joints are complicated by the viscoelastic nature of the connective tissues joining vertebrae, and by multiple vertebral articulations and complex morphologies. Further, interspecific variation in these structures can greatly compound their functional variation between species, making comparative mechanical analyses even more difficult. Despite these sources of variation however, mammalian intervertebral joints universally exhibit a creep relaxation behaviour based on the viscoelastic nature of the soft tissue joint. We have evaluated, in 6 degrees of freedom, the mechanical signature of a novel mammalian lumbar intervertebral joint found in the Scutisorex spine, and compared it with a more typical mammalian joint in the Rattus (rat) lumbar spine. Scutisorex, the hero shrew, is an East African species of shrew with what is likely the most highly modified vertebral morphology in the entire history of mammals. Thus we decided to evaluate the mechanical behaviour of the intervertebral joint of this species, comparing it with a more representative mammal species in Rattus. We built a custom, 6 degrees of freedom, intervertebral joint transducer and a combined axial moment and load application system in order to quantify and compare the complex mechanical behaviour of these joints. Our results suggest that the Scutisorex joint is 5 times more resilient to simple axial torsion per body mass unit than Rattus, and that the complex load (combined axial compression and torsion) mechanical signature of Scutisorex is probably novel among all mammalian intervertebral joints. Under significant but physiological axial compression the Scutisorex intervertebral joint demonstrates no creep relaxation behaviour, simulating the mechanical behaviour of a rigid construct rather than a viscoelastic joint. The purpose of this rigid intervertebral joint in the ecology of Scutisorex remains unknown.

Four major morphologically distinct classes of cells were identified within the adult rabbit meniscus using antibodies to cytoskeletal proteins. Two classes of cell were present in the fibrocartilage region of the meniscus. These meniscal cells exhibited long cellular processes that extended from the cell body. A third cell type found in the inner hyaline-like region of the meniscus had a rounded form and lacked projections. A fourth cell type with a fusiform shape and no cytoplasmic projections was found along the superficial regions of the meniscus. Using a monoclonal antibody to connexin 43, numerous gap junctions were observed in the fibrocartilage region, whereas none were seen in cells either from the hyaline-like or the superficial zones of the meniscus. The majority of the cells within the meniscus exhibited other specific features such as primary cilia and 2 centrosomes. The placement of the meniscal cell subtypes as well as their morphology and architecture support the supposition that their specific characteristics underlie the ability of the meniscus to respond to different types of environmental mechanical loads.

The friction coefficients measured in diarthrodial joints are small. Theories of joint lubrication attribute this efficiency to entrapment or movement of synovial fluid, yet anatomical models of the surface are based on studies of isolated fragments of cartilage, not functional joints. To investigate the functional interrelationship of joint surfaces and synovial fluid, the ultrastructure of loaded joints was examined. Twenty-four New Zealand white rabbit knee joints were loaded either statically or moved ex vivo using simulated muscle forces and then plunge-frozen under load. After fixation in the frozen/loaded state by freeze-substitution fixation, the medial joint compartments were embedded in epoxy resin while still articulated. Bone was trimmed away from the articular surfaces, permitting the cartilage to be sectioned for light and electron microscopy. These joint surfaces were then compared with controls which were not loaded, not moved or had been disarticulated prior to embedding. Articular surfaces of loaded joints were smooth at magnifications from ×35 to ×7500, whereas the tibial surfaces of nonloaded joints were irregular. Small pools of joint fluid were observed at the meniscal edge and beneath the anterior horn of the meniscus. At magnifications of ×40000, the joint surfaces were separated by a uniform 100 nm space containing fluid. An amorphous, electron dense articular surface lamina was present but, when loaded, was thicker and flatter than previously reported. No surface pits or bumps were visible in embedded, loaded joints. This is the first ultrastructural study of intact loaded joints. The findings suggest that fluid film lubrication is present in diarthrodial joints, but the fluid sequestration postulated in several models is not apparent.

The subchondral bone plate supports the articular cartilage in diarthrodial joints. It has a significant mechanical function in transmitting loads from the cartilage into the underlying cancellous bone and has been implicated in the destruction of cartilage in osteoarthritis (OA) and its sparing in osteoporosis (OP), but little is known of its composition, structure or material properties. This study investigated the microscopic appearance and mineral composition of the subchondral bone plate in femoral heads from patients with OA or OP to determine how these correspond to changes in composition and stiffness found in other studies. Freeze-fractured full-depth samples of the subchondral bone plate from the femoral heads of patients with osteoarthritis, osteoporosis or a matched control group were examined using back scattered and secondary emission scanning electron microscopy. Other samples were embedded and polished and examined using back-scattered electron microscopy and electron probe microanalysis. The appearances of the samples from the normal and osteoporotic patients were very similar, with the subchondral bone plate overlayed by a layer of calcified cartilage. Osteoporotic samples presented a more uniform fracture surface and the relative thicknesses of the layers appeared to be different. In contrast, the OA bone plate appeared to be porous and have a much more textured surface. There were occasional sites of microtrabecular bone formation between the trabeculae of the underlying cancellous bone, which were not seen in the other groups, and more numerous osteoclast resorption pits. The calcified cartilage layer was almost absent and the bone plate was apparently thickened. The appearance of the osteoarthritic subchondral bone plate was, therefore, considerably different from both the normal and the osteoporotic, strongly indicative of abnormal cellular activity.

We sought to study the effect of synovectomy on the surface morphology of articular cartilages of the rabbit knee using scanning electron microscopy (SEM). Fifteen rabbits were surgically synovectomised and allowed to regenerate their synovia during time intervals ranging from 3 to 44 wk. Cartilage specimens were shaved from 5 distinct articular sectors of synovectomised, contralateral and sham-operated knees and prepared for SEM using tannic acid. Applying structural reinforcement by tannic acid was found to secure the in vivo surface morphology of the cartilages and thus production of surface irregularities during preparation was excluded. The surface morphology of cartilages both from the synovectomised and contralateral joints was found to differ from that of intact healthy rabbits. A ‘chaotic’ nature of the altered cartilaginous morphology persisted as late as 44 wk postsynovectomy. Cartilages from sham-operated joints did not differ detectably from normal cartilages.