scholarly journals Photogrammetric evaluation of shear modulus of glulam timber using torsion test method and dual stereo vision system

2021 ◽  
Author(s):  
Ahmed Mohamed ◽  
Yu Deng ◽  
Hexin Zhang ◽  
Simon H. F. Wong ◽  
Kal Uheida ◽  
...  
Keyword(s):  
Shear Modulus ◽  
Vision System ◽  
Torsion Test ◽  
Wood Products ◽  
Test Method ◽  
Three Dimensions ◽  
Contact Method ◽  
Camera System ◽  
Anticlockwise Direction ◽  
Timber Beams

AbstractThe shear modulus of timber and timber-based composite materials is a fundamental mechanical property, which is used in the design of timber and engineered wood products. The problem of experimentally determining appropriate values of shear modulus for timber-based composite is not as simple and straightforward as in isotropic materials. Although the torsion test is a recommended standard approach to determine the shear modulus of structural-size timber and glulam beams, it is difficult to measure the rotational deformations of the timber beams. Therefore, in this paper, a stereo camera system combined with a photogrammetric approach is proposed to evaluate the values and variations of the shear modulus of glulam beams under the torsion test. The photogrammetric approach is a non-contact method, which provides an efficient and alternative approach for measuring the deformations of the torsion specimens in three dimensions. A series of experiments was conducted on glulam timber beams under the torsion test to investigate the applicability of the optical approach to evaluate the values and variations of shear modulus as well as to investigate the effect of applying torques in a clockwise or anticlockwise direction on the shear modulus of the beams. This optical system not only allows the performance and reliability of the traditional sensors to be assessed, but also allows the rotational deformation of the torsion samples to be monitored at various locations. This enables the values of shear modulus at different cross-sections of the torsion specimens to be evaluated without the need to use more devices. The test results showed that applying torques to the glulam timber specimens during loading and unloading in either a clockwise or anticlockwise direction does not influence or cause a significant change in the shear modulus of the beams. By comparing shear modulus values of glulam beams measured based on different shear spans, it was found that the larger the shear span the smaller the shear modulus value. This might indicate that the variations of shear modulus values at these different gauge lengths need to be considered.

scholarly journals Photogrammetric Evaluation of Shear Modulus of Glulam Timber Using Torsion Test Method and Dual Stereo Vision System

2021 ◽  
Author(s):  
Ahmed Mohamed ◽  
Yu Deng ◽  
Hexin Zhang ◽  
Simon H F Wong ◽  
Kal Uheida ◽  
...  
Keyword(s):  
Shear Modulus ◽  
Vision System ◽  
Torsion Test ◽  
Wood Products ◽  
Test Method ◽  
Three Dimensions ◽  
Contact Method ◽  
Camera System ◽  
Anticlockwise Direction ◽  
Timber Beams

Abstract The shear modulus of timber and timber-based composite materials is a fundamental mechanical property which is used in the design of timber and engineered wood products. The problem of experimentally determining appropriate values of shear modulus for timber-based composite is not as simple and straightforward as in isotropic materials. Although the torsion test is a recommended standard approach to determine the shear modulus of structural-size timber and glulam beams, it is a difficult to measure the rotational deformations of the timber beams. Therefore, in this paper, a stereo camera system combined with a photogrammetric approach is proposed to evaluate the values and variations of the shear modulus of glulam beams under the torsion test. The photogrammetric approach is a non-contact method which provides an efficient and alternative approach for measuring the deformations of the torsion specimens in three dimensions. A series of experiments were conducted on glulam timber beams under the torsion test to investigate the applicability of the optical approach to evaluate the values and variations of shear modulus as well as to investigate the effect of applying torques in a clockwise or anticlockwise direction on the shear modulus of the beams. This optical system not only allows the performance and reliability of the traditional sensors to be assessed, but also allows the rotational deformation of the torsion samples to be monitored at various locations. This enables the values of shear modulus at different cross-sections of the torsion specimens to be evaluated without the need to use more devices. The test results showed that applying torques to the glulam timber specimens during loading and unloading in either a clockwise or anticlockwise direction does not influence or cause a significant change in the shear modulus of the beams. By comparing shear modulus values of glulam beams measured based on different shear spans, it was found that the larger the shear span the smaller the shear modulus value. This might indicate that the variations of shear modulus values at these different gauge lengths needs to be considered.

scholarly journals Verification of the photogrammetric approach on the torsion test method for timber beams

2021 ◽  
pp. 1-12
Author(s):  
Ahmed Mohamed ◽  
Kal Uheida ◽  
Yanfang Quan ◽  
Hexin Zhang
Keyword(s):  
Torsion Test ◽  
Test Method ◽  
Timber Beams

Parachute Swing Angle Measurement in Wind Tunnel Test Based on Stereo Vision System

2013 ◽  
Vol 380-384 ◽  
pp. 837-840
Author(s):  
Jin Song ◽  
Jun Ma ◽  
Min Jiang
Keyword(s):  
Wind Tunnel ◽  
Stereo Vision ◽  
Measurement Problem ◽  
Vision System ◽  
Wind Tunnel Test ◽  
Angle Measurement ◽  
Test Method ◽  
Swing Angle ◽  
Stereo Vision System ◽  
Parachute System

Parachute system is a significant composing part of aircraft, and the swing angle is one of system security targets. To the complicated measurement problem of parachute angle in wind tunnel test, this paper describes a test method based on stereo vision system, the system is mainly composed of two CCD cameras, image acquisition card and computer. It can get 3D coordinates by stereo vision calibration and digital image processing technology, and calculate the parachute swing angle by geometry relationship. The result shows that the method succeeds, and gets the vertical and horizontal angles which are projected onto two orthogonal planes. The method has the advantage of simple system composing and good compatibility, displays much better application value.

Using Torsion Bar Testing to Determine Fracture Toughness of Ceramic Materials

2002 ◽  
Author(s):  
J. A. Wang ◽  
K. C. Liu ◽  
G. A. Joshi
Keyword(s):  
Fracture Toughness ◽  
Crack Opening ◽  
Torsion Test ◽  
Ceramic Materials ◽  
Type Specimen ◽  
Small Region ◽  
Fracture Load ◽  
Test Method ◽  
Finite Element Program ◽  
Spiral Line

A new method, designated as Spiral Notch Torsion Test (SNoTT), is introduced for determining fracture toughness KIC of materials ranging from metallic alloys to brittle ceramics and their composites. A round-rod specimen having a V-grooved spiral line with a 45° pitch is subjected to pure torsion. This loading configuration creates a uniform tensile-stress crack-opening mode, Mode-I, with a transverse plane-strain state along the grooved line. This technique is analogous to the conventional test method using a compact-type specimen with a thickness equivalent to the full length of the spiral line. KIC values are determined from the fracture load and crack length with the aid of an in-house developed 3-D finite element program (TOR3D-KIC). A mixed mode (modes I and III) fracture toughness value can be determined by varying the pitch of the spiral line or varying the ratio of axial to torsion loads. Since the key information needed for determining KIC values is manifested within a small region near the crack tip, the specimen can be significantly miniaturized without the loss of generality. Limited results obtained for various materials are compared with published KIC values, showing differences of less than 2% in general and 6% maximum in one case. The experimental technique and theoretical basis of the proposed method are presented in detail.

Validation of an Improved Contact Method for Multi-Material Eulerian Hydrocodes in Three-Dimensions

2019 ◽  
Author(s):  
Kenneth C. Walls ◽  
David L. Littlefield
Keyword(s):  
Finite Element ◽  
Large Deformations ◽  
Three Dimensions ◽  
Contact Method ◽  
Arbitrary Lagrangian Eulerian ◽  
Aspect Ratios ◽  
Ale Methods ◽  
Lagrangian Finite Element ◽  
Multiple Materials ◽  
Natural Description

Abstract Realistic and accurate modeling of contact for problems involving large deformations and severe distortions presents a host of computational challenges. Due to their natural description of surfaces, Lagrangian finite element methods are traditionally used for problems involving sliding contact. However, problems such as those involving ballistic penetrations, blast-structure interactions, and vehicular crash dynamics, can result in elements developing large aspect ratios, twisting, or even inverting. For this reason, Eulerian, and by extension Arbitrary Lagrangian-Eulerian (ALE), methods have become popular. However, additional complexities arise when these methods permit multiple materials to occupy a single finite element.

scholarly journals A Methodology for Multi-Camera Surface-Shape Estimation of Deformable Unknown Objects

Robotics ◽  
2018 ◽  
Vol 7 (4) ◽  
pp. 69 ◽  
Author(s):  
Evgeny Nuger ◽  
Beno Benhabib
Keyword(s):  
Particle Filtering ◽  
Surface Deformation ◽  
Vision System ◽  
Three Dimensional ◽  
Target Object ◽  
Surface Shape ◽  
Shape Estimation ◽  
Formal Approach ◽  
Camera System ◽  
Unknown Objects

A novel methodology is proposed herein to estimate the three-dimensional (3D) surface shape of unknown, markerless deforming objects through a modular multi-camera vision system. The methodology is a generalized formal approach to shape estimation for a priori unknown objects. Accurate shape estimation is accomplished through a robust, adaptive particle filtering process. The estimation process yields a set of surface meshes representing the expected deformation of the target object. The methodology is based on the use of a multi-camera system, with a variable number of cameras, and range of object motions. The numerous simulations and experiments presented herein demonstrate the proposed methodology’s ability to accurately estimate the surface deformation of unknown objects, as well as its robustness to object loss under self-occlusion, and varying motion dynamics.

Slow Crack Growth in Dental Composites

1985 ◽  
Vol 55 ◽  
Author(s):  
G. M. Montes-G. ◽  
R. A. Draughn ◽  
T. H. Simpson
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
Slow Crack Growth ◽  
High Stress ◽  
Torsion Test ◽  
Stable Crack Growth ◽  
Test Method ◽  
Volume Percent ◽  
Stick Slip ◽  
Model Composite

ABSTRACTThe fracture properties of selected commercial composite dental restorative materials and a model composite system were studied to determine the influences of the reinforcing phase, exposure to water, and particle/polymer adhesion on crack propagation. The content of inorganic fillers ranged from 36 to 62 volume percent. In the model system the polymer phase approximated that of the commercial products, a constant size distribution of quartz fillers was used, and polymer/particle adhesion was varied. The double torsion test method was employed to measure relationships between applied stress intensity factor and velocity of crack propagation during stable crack growth. In all systems, cracks propagated through regions of high stress concentration at the low end of the velocity range studied (10−7 m/sec to 10−3 m/sec). Wet materials fractured at lower stress intensities than dry materials at all velocities. At high velocities unstable (stick-slip) growth occurred in dry materials with strong filler/matrix interfaces and in wet specimens with initially strong interfaces and less than 41 volume percent filler. In wet conditions, materials with poorly bonded fillers fractured by slow crack growth at stress intensities 10% to 30% below the levels of composites with strong interfaces.

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