A new method to determine the beam bending creep critical displacement of three-point bending specimen with fixed constraints

A new method of indicating contact damage of composite materials, using a polymer retroreflective film (PRF) with micro-prisms, is proposed. Impact contact action leads to deformation of microprisms and with directed lighting allows seeing the place of impact in the form of a dark spot. In experimental studies, using STEF fibreglass as an example, the dependences of the spot diameter on the contact pressure up to 530 MPa were studied. An assessment of the residual strength and stiffness of a composite specimen-beam with a contact defect was obtained with three-point bending. It is shown that, during bending, the strength of STEF with contact defects decreases from 615 to 386 MPa. The data obtained allow to assess the danger of contact pressure by the known diameter of the dark spot on the PRF.

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Research on the Conversion Relationship for Three-Point Bending Specimen With Fixed Constraints in the Large Deformation Stage

Journal of Pressure Vessel Technology ◽

10.1115/1.4044534 ◽

2019 ◽

Vol 141 (6) ◽

Author(s):

Hai-Yang Yu ◽

Guo-Yan Zhou ◽

Fa-Kun Zhuang

Keyword(s):

Large Deformation ◽

Creep Test ◽

Geometric Parameters ◽

Test Method ◽

Three Point Bending ◽

Deformation Stage ◽

Creep Stress ◽

Uniaxial Creep ◽

Conversion Coefficients ◽

Beam Bending

Abstract In this study, based on the rod tensile model, a conversion relationship between three-point bending specimen with fixed constraints (TPBSF) and uniaxial creep data in the large deformation stage is defined by the reference stress method. Using finite element method, conversion coefficients are determined. Then it is verified by the creep test data of A7N01 at 350 °C (Zhuang, F. K., 2014, “Research on Creep Test Method of Small Specimen Based on Beam Bending Theory,” Ph.D. thesis, East China University of Science and Technology, Shanghai, China). The results show that creep stress exponent n is the same, but creep constant B obtained by rod tensile model is much closer to uniaxial creep than beam bending model. Finally, effects of geometric parameters and friction on conversion coefficients are investigated. On this basis, the specimen cross section aspect ratio greater than 1 and the indenter radius larger than 1 mm are recommended to minimize the influence of TPBSF geometric parameters on conversion coefficients. The influence of friction on conversion coefficients can be negligible.

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A New Approach to Manufacturing Biocomposite Sandwich Structures: Investigation of Preform Shell Behavior

Journal of Manufacturing Science and Engineering ◽

10.1115/1.4034278 ◽

2016 ◽

Vol 139 (2) ◽

Cited By ~ 8

Author(s):

Lai Jiang ◽

Daniel Walczyk ◽

Gavin McIntyre

Keyword(s):

Natural Fiber ◽

Sandwich Structures ◽

Maximum Tensile Stress ◽

Fungal Mycelium ◽

Test Results ◽

Mycelium Growth ◽

Growth Environment ◽

Three Point Bending ◽

Beam Bending ◽

Full Factorial Experimental Design

The manufacture of natural fiber and core preforms for biocomposite sandwich structures that bound together with fungal mycelium-based polymer is investigated. The complete manufacturing process involves: (1) cutting individual textile plies; (2) impregnating multi-ply layups with natural glue conducive to mycelium growth; (3) simultaneously forming, sterilizing and setting impregnated skins; (4) filling formed skins with mycelium-laden agri-waste; (5) allowing mycelium to colonize and bind together core substrate and skins into a unitized preform; (6) high temperature drying that also inactivates fungus; and (7) infusing skins with bioresin using resin transfer molding. Aspects of steps 3–6 related to the preform shells and sandwich structure are the main focus of this paper. Three-point bending tests are performed on dry, natural glue-bonded, four-ply specimens in a full-factorial experimental design, and test results are analyzed by analysis of variance (ANOVA) to assess process parameter effects and sensitivities along with environmental condition effects. New specimens are then made using the optimized process and tested for beam bending in creep within an environmental chamber that mimics the actual mycelium growth environment for three days. Two- and six-ply specimens loaded to provide identical maximum tensile stress in flexure are tested, and useful conclusions are drawn based on all creep test results. Finally, preforms in the shape of a viable commercial product are filled with mycelium-inoculated substrate, grown and dried, and part quality is evaluated based on the amount of skin ingrowth and deviation between the measured and desired shapes.

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Stiction of Flexural MEMS Structures

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.190-191.794 ◽

2012 ◽

Vol 190-191 ◽

pp. 794-800

Author(s):

Yun Liu ◽

Yin Zhang

Keyword(s):

Boundary Conditions ◽

External Load ◽

Virtual Work ◽

Ritz Method ◽

New Method ◽

Beam Deflection ◽

New Model ◽

Arc Shape ◽

Beam Bending ◽

Microcantilever Beam

A variational method using the principle of virtual work (PVW) is presented to formulate the problem of the microcantilever stiction. Compared with the Rayleigh–Ritz method using the arc-shaped or S-shaped deflection, which prescribes the boundary conditions and thus the deflection shape of a stuck cantilever beam, the new method uses the matching conditions and constraint condition derived from PVW and minimization of the system free energy to describe the boundary conditions at the contact separation point. The transition of the beam deflection from an arc-shape-like one to an S-shape-like one with the increase of the beam length is shown by the new model. The (real) beam deflection given by this new model deviates more or less from either an arc-shape or an S-shape, which has significant impact on the interpretation of experimental data. The arc-shaped or S-shaped deflection assumption ignores the beam bending energy inside the contact area and the elastic energy due to the beam/substrate contact, which is inappropriate as shown by this study. Furthermore, the arc-shaped or S-shaped deflection only approximately describes the deflection shape of a stuck beam with zero external load and obviously, the external load changes the beam deflection. The Rayleigh–Ritz method using the arc-shaped or S-shaped deflection assumption in essence can only be used to tell approximately whether stiction occurs or not. Rather than assuming a certain deflection shape and by incorporating the external load, the new method offers a more general and accurate study not only on the microcantilever beam stiction but also on its de-adherence.

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Incremental Bending of Three-Dimensional Free Form Metal Plates Using Minimum Energy Principle and Model-Less Control

Journal of Manufacturing Science and Engineering ◽

10.1115/1.4035796 ◽

2017 ◽

Vol 139 (7) ◽

Cited By ~ 9

Author(s):

Xiaobing Dang ◽

Kai He ◽

Wei Li ◽

Qiyang Zuo ◽

Ruxu Du

Keyword(s):

Computer Vision ◽

Minimum Energy ◽

Three Dimensional ◽

Metal Plate ◽

New Method ◽

Free Form ◽

Energy Principle ◽

Minimum Energy Principle ◽

Metal Plates ◽

Beam Bending

Bending 3D free form metal plates is a common process used in many heavy industries such as shipbuilding. The traditional method is the so-called line heating method, which is not only labor intensive but also inefficient and error-prone. This paper presents a new incremental bending method based on minimum energy principle and model-less control. First, the sheet metal is discretized into a number of strips connected through virtual springs. Next, by applying the minimum energy principle, the punching and supporting points are calculated for the strip. Then, the bended shape of the strip is computed based on the beam bending theory. This process is continued until the final shape is reached. To compensate the bending error, the computer vision-based model-less control is applied. The computer vision detects the bending error based on which additional bending steps are calculated. The new method is tested in a custom build incremental bending machine. Different metal plates are formed. For a metal plate of 1000 × 800 × 5 mm3, the average bending error is less than 3 mm. In comparison with the existing methods, the new method has a number of advantages, including simple, fast, and highly energy efficient.

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Selective Sampling and Orientation of Non-Homogeneous Tissues

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100100238 ◽

1968 ◽

Vol 26 ◽

pp. 98-99

Author(s):

C. C. Clawson ◽

L. W. Anderson ◽

R. A. Good

Keyword(s):

Electron Microscopy ◽

Electron Microscope ◽

Light Microscopy ◽

Random Sampling ◽

New Method ◽

Microscope Examination ◽

Small Areas ◽

Selective Sampling ◽

Large Numbers ◽

Specific Orientation

Investigations which require electron microscope examination of a few specific areas of non-homogeneous tissues make random sampling of small blocks an inefficient and unrewarding procedure. Therefore, several investigators have devised methods which allow obtaining sample blocks for electron microscopy from region of tissue previously identified by light microscopy of present here techniques which make possible: 1) sampling tissue for electron microscopy from selected areas previously identified by light microscopy of relatively large pieces of tissue; 2) dehydration and embedding large numbers of individually identified blocks while keeping each one separate; 3) a new method of maintaining specific orientation of blocks during embedding; 4) special light microscopic staining or fluorescent procedures and electron microscopy on immediately adjacent small areas of tissue.

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