PubMed Health⌕ Search

PubMed · 10853759

Graphical statics a forgotten tool for solving plane mechanical problems.

Abstract

Graphical statics is an almost forgotten, intuitive drawing method for solving plane mechanical problems. It was already in use in the 19th century for biomechanical problems. It was still a standard method employed by civil engineers in the 1940s. Superceded by modern analytical methods, graphical statics disappeared almost completely. The method is restricted to plane static problems, but still remains a useful tool for visualizing, understanding and checking the actions of force groups occurring in modern biomechanical problems. After defining the basic mechanical terminology (body, motion, forces), the paper is written mainly as a teaching tool for immediate application. Many illustrative examples (sporting activities, functional forces in joints) help to clarify the difficult biomechanical content. For application, it must be assumed that the bodies investigated behave as rigid bodies under the action of the forces, but this does not prevent application of the method to deformable living bodies if specific static configurations of the bodies are considered. The application of the method requires a good anatomical knowledge and experience with the function of the musculoskeletal apparatus of living bodies. If reliable models are used, the method delivers quantitative results of sufficient accuracy. The paper may also help provide a better understanding of publications containing graphical solutions to bio-static problems.

Explore related subjects

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

E Baumgart. 2000. Graphical statics a forgotten tool for solving plane mechanical problems.. https://doi.org/10.1016/s0020-1383(00)80041-8

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

Forces associated with pneumatic power screwdriver operation: statics and dynamics.

The statics and dynamics of pneumatic power screwdriver operation were investigated in the context of predicting forces acting against the human operator. A static force model is described in the paper, based on tool geometry, mass, orientation in space, feed force, torque build up, and stall torque. Three common power hand tool shapes are considered, including pistol grip, right angle, and in-line. The static model estimates handle force needed to support a power nutrunner when it acts against the tightened fastener with a constant torque. A system of equations for static force and moment equilibrium conditions are established, and the resultant handle force (resolved in orthogonal directions) is calculated in matrix form. A dynamic model is formulated to describe pneumatic motor torque build-up characteristics dependent on threaded fastener joint hardness. Six pneumatic tools were tested to validate the deterministic model. The average torque prediction error was 6.6% (SD = 5.4%) and the average handle force prediction error was 6.7% (SD = 6.4%) for a medium-soft threaded fastener joint. The average torque prediction error was 5.2% (SD = 5.3%) and the average handle force prediction error was 3.6% (SD = 3.2%) for a hard threaded fastener joint. Use of these equations for estimating handle forces based on passive mechanical elements representing the human operator is also described. These models together should be useful for considering tool handle force in the selection and design of power screwdrivers, particularly for minimizing handle forces in the prevention of injuries and work related musculoskeletal disorders.

Biomechanical Phenomena↗

Biomechanics of the PCL and related structures: posterolateral, posteromedial and meniscofemoral ligaments.

This paper reviews and updates our knowledge of the anatomy and biomechanics of the posterior cruciate ligament, and of the posterolateral, posteromedial and meniscofemoral ligaments of the knee. The posterior cruciate ligament is shown to have two functional fibre bundles that are tight at different angles of knee flexion. It is the primary restraint to tibial posterior draw at all angles of knee flexion apart from near full extension. In contrast, the posterolateral and posteromedial structures are shown to tighten as the knee extends, and to be well-aligned to resist tibial posterior draw. These structures also act as primary restraints against other tibial displacements. Tibial internal rotation is restrained by the medial and posteromedial structures, while tibial external rotation is restrained by the lateral and posterolateral structures. They are also the primary restraints against tibial abduction-adduction rotations. The meniscofemoral ligaments are shown, for the first time, to contribute significantly to resisting tibial posterior draw, and to have a strength of approximately 300 N. Taken together, this evidence shows how the posterolateral and posteromedial structures are responsible for posterior knee stability near extension, and this, along with the action of the meniscofemoral ligaments, may explain why an isolated rupture of the posterior cruciate ligament does not often lead to knee instability

Biomechanical Phenomena↗

Unreamed tibia nail (UTN) bending: case report and problem solution.

BACKGROUND: An unreamed tibia nail (UTN), implanted for operative stabilization of the tibia after a distal shaft fracture of the lower leg, was bent by excessive load prematurely applied during the healing process, whereby the cross-section-dependent maximum torque permitted in the edge fiber of the UTN during bending load was exceeded. Straightening of the bent, not broken UTN by hand was impossible. Therefore, the bent UTN could only be removed by causing additional damage to the tibia, which is why bending of the nail must be avoided. CONCLUSION: Our analysis shows that modification of the arrangement of the locking holes by 45 degrees increases bending load capacity of the UTN, which can minimize the probability of the occurrence of a bent nail.

Biomechanical Phenomena↗