China
Africa
Explore chapters and articles related to this topic
Stochastic Free Vibration Analysis of Pre-twisted Singly Curved Composite Shells
Published in Sudip Dey, Tanmoy Mukhopadhyay, Sondipon Adhikari, Uncertainty Quantification in Laminated Composites, 2018
Sudip Dey, Tanmoy Mukhopadhyay, Sondipon Adhikari
Composite singly curved shells are widely used in various engineering applications. Analyzing the effect of twist angle in such structures is immensely important for applications in turbomachinery blades, wind turbines and various aircraft components. Composite structures are often pretwisted due to design and operational needs such as the wing twist of an aircraft is provided to maintain optimum angle of attack preventing negative lift or thrust and maximizing the aerodynamic efficiency. The production of composite structures is always subjected to large variability due to manufacturing imperfection (both structural and material attributes) and operational factors. It is essential to estimate the probabilistic variability in the dynamic responses to ensure the safety and serviceability conditions.
Torsion members
Published in N. S. Trahair, M. A. Bradford, The Behaviour and Design of Steel Structures to AS 4100, 2017
In elastic uniform torsion, the twist rotation per unit length is constant along the length of the member. This occurs when the torque is constant and the ends of the member are free to warp, as shown in Fig. 10.1a. When a member twists in this way: lines which were originally parallel to the axis of twist become helices,cross-sections rotate φ as rigid bodies about the axis of twist,cross-sections warp out of their planes, the warping deflections w being constant along the length of the member (see Fig. 10.4).
Kinematic Design
Published in Richard Leach, Stuart T. Smith, Basics of Precision Engineering, 2017
In fact, screw displacement provides a powerful description of spatial displacement and forms the basis of ‘screw theory’ or Chasles’ theorem (Jazar 2007). The theorem states that every spatial displacement is the composition of a rotation about some axis and a translation along the same axis. A few terms are important to describe this theorem. A screw is a line or axis with an associated pitch, which is a ratio of linear to angular quantities. A twist is a screw plus a scalar magnitude, providing a rotation about the screw axis and a translation along the screw axis. The rotation angle is the twist magnitude and the translation distance is the twist magnitude multiplied by the pitch (hence, pitch is the ratio of translation to rotation). Thus Chasles’ theorem can be re-stated as every spatial displacement is a twist about some screw (Mason 2001).
Space-curve Cartan matrix and exact differentiability of the curvature and torsion
Published in Mechanics Based Design of Structures and Machines, 2023
Space-curve curvature is used in linear and nonlinear formulations of beam vibration equations to formulate strain energy and elastic forces. Curve torsion is result of out-of-plane bending that produces twist to be distinguished from continuum-mechanics shear mode. Nonetheless, the curvature and torsion are not, in general, associated with derivatives of angles because they are elements of Cartan matrix and are not exact differentials. Curve twist, for example, is result of coupled in-plane and out-of-plane bending modes, which can be described mathematically using two rotations. As discussed in this paper, a curve can be twisted without performing a rotation about curve tangent; example of such a curve is the helix curve. Because different frames were introduced to overcome problem of defining Frenet frame at curvature-vanishing points, Cartan matrix can have different structures that depend on the condition used to define the frame. Frenet angles are used in this study to develop simple and general expressions for the curvature and torsion. Two different rotation sequences are used to demonstrate that the curvature and torsion are not exact differentials. The analysis and results presented in this investigation demonstrate fundamental difference between Bishop shear angle and Frenet bank angle. Uniqueness of Bishop shear angle and Bishop frame are discussed
Investigating the co-effect of twist and hot drawing processes on the bio-based yarns properties
Published in The Journal of The Textile Institute, 2020
In fact, the drawing process runs at a higher speed than the melt spinning speed. Therefore, the drawing process is a separate operation from the spinning line (Stevens, 1986). With twisting the yarn, each yarn runs from a bobbin via a supply roller through a guide into the twisting balloon, and then through a running traveller tangentially onto the bobbin (Lawrence, 2010). When twist stage is applied to multifilament yarn, the freedom of the filament to move is reduced as the yarn has stiffer cohesion (Brody, 1994). Twist causes the outer filaments to press on inner one (filaments exert pressure on each other), which helps the filaments to share the load and increases the strength (Lawrence, 2003). When one of the filaments is broken, its friction with the neighbouring filaments enables the broken one (Younes, 2015). Two general lines were used in the current research to produce single untwisted and twisted yarns. First, the effect of the multi-stage hot drawing process on crystallographic order and chain orientation and the thermal and mechanical properties of untwisted yarns were statistically investigated and characterized. Secondly, continuous drawn filaments yarns had been twisted.
Effect of gauge length on loop strength of sewing threads
Published in The Journal of The Textile Institute, 2019
Vinay Kumar Midha, Ashish Kumar Gupta, A. Mukhopadhyay
The twist per unit length is measured using a direct counting method according to ASTM standard D1423. Tensile testing of the threads is performed at a gauge length of 250 mm on a Tinius Oleson universal testing machine as per ASTM standard D2256. Thirty tests are carried out and the error at the 95% confidence level is less than 4%. Thread strength and loop strength tests are carried out at different gauge lengths (50, 100, 150, 200, 250, and 2.5 mm) using a test speed, corresponding to 20s breaking time for all the threads. About 50 tests of each sample are done and the mean value is calculated. Statistical significant testing is carried out at 95% confidence level to investigate whether the mean values of thread strength and loop strength at successive gauge lengths are statistically significant with respect to the mean values in the lower gauge length. Tukey’s test is used to find the statistical significance. The Tukey’s test (or Tukey procedure), also called Tukey’s honest significant difference test, is a post hoc test based on the studentized range distribution. Tukey’s HSD compares all possible pairs of means to find out which specific groups means (compared with each other) are statistically different. For pair wise comparisons amongst the means, Tukey’s HSD for each pair of means is calculated using Equation (1):