scholarly journals Failure mechanism of hollow tree trunks due to cross-sectional flattening

2017 ◽  
Vol 4 (4) ◽  
pp. 160972 ◽  
Author(s):  
Yan-San Huang ◽  
Fu-Lan Hsu ◽  
Chin-Mei Lee ◽  
Jia-Yang Juang
Keyword(s):  
Urban Areas ◽  
Failure Modes ◽  
Shear Failure ◽  
Maximum Shear Stress ◽  
Mode Iii ◽  
Buckling Mode ◽  
Cross Sectional ◽  
Longitudinal Splitting ◽  
Bending Failure ◽  
Hollow Tree

Failure of hollow trees in urban areas is a worldwide concern, and it can be caused by different mechanisms, i.e. bending stresses or flattening-related failures. Here we derive a new analytical expression for predicting the bending moment for tangential cracking, and compare the breaking moment of various failure modes, including Brazier buckling, tangential cracking, shear failure and conventional bending failure, as a function of t / R ratio, where t and R are the trunk wall thickness and trunk radius, respectively, of a hollow tree. We use Taiwan red cypress as an example and show that its failure modes and the corresponding t / R ratios are: Brazier buckling (Mode I), tangential cracking followed by longitudinal splitting (Mode II) and conventional bending failure (Mode III) for 0 <  t / R  < 0.06, 0.06 <  t / R  < 0.27 and 0.27 <  t / R  < 1, respectively. The exact values of those ratios may vary within and among species, but the variation is much smaller than individual mechanical properties. Also, shear failure, another type of cracking due to maximum shear stress near the neutral axis of the tree trunk, is unlikely to occur since it requires much larger bending moments. Hence, we conclude that tangential cracking due to cross-sectional flattening, followed by longitudinal splitting, is dominant for hollow trunks. Our equations are applicable to analyse straight hollow tree trunks and plant stems, but are not applicable to those with side openings or those with only heart decay. Our findings provide insights for those managing trees in urban situations and those managing for conservation of hollow-dependent fauna in both urban and rural settings.

Experimental investigation and modeling of dynamic thermomechanical behavior of 4-harness satin weave carbon/epoxy composites

2017 ◽  
Vol 31 (9) ◽  
pp. 1181-1203 ◽  
Author(s):  
Xueyao Hu ◽  
Hui Guo ◽  
Weiguo Guo ◽  
Feng Xu ◽  
Longyang Chen ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Composite Laminates ◽  
Failure Modes ◽  
Shear Failure ◽  
Experimental Studies ◽  
Temperature Shift ◽  
Thermomechanical Coupling ◽  
Longitudinal Splitting ◽  
Wide Range

Theoretical and experimental studies on the compressive mechanical behavior of 4-harness satin weave carbon/epoxy composite laminates under in-plane loading are conducted over the temperature range of 298–473 K and the strain rate range of 0.001–1700/s in this article. The stress–strain curves of 4-harness satin weave composites are obtained at different strain rates and temperatures, and key mechanical properties of the material are determined. The deformation mechanism and failure morphology of the samples are observed and analyzed by scanning electron microscope (SEM) micrographs. The results show that the uniaxial compressive mechanical properties of 4-harness satin weave composites are strongly dependent on the temperature but are weakly sensitive to strain rate. The peak stress and elastic modulus of the material have the trend of decrease with the increasing of temperature, and the decreasing trend can be expressed as the functional relationship of temperature shift factor. In addition, SEM observations show that the quasi-static failure mode of 4-harness satin weave composites is shear failure along the diagonal lines of the specimens, while the dynamic failure modes of the material are multiple delaminations and longitudinal splitting, and with the increasing of temperature, its longitudinal splitting is more serious, but the delamination is relatively reduced. A constitutive model with thermomechanical coupling effects is proposed based on the experimental results and the increment theory of elastic–plastic mechanics. The experimental verification and numerical analysis show that the model is shown to be able to predict the finite deformation behavior of 4-harness satin weave composites over a wide range of temperatures.

Experimental Research on Four-Tube Concrete-Filled Steel Tubular Laced Columns

2011 ◽  
Vol 311-313 ◽  
pp. 2204-2207 ◽  
Author(s):  
Bo Wang Chen ◽  
Ran He ◽  
Jian Guo Tan ◽  
Yang Oyang
Keyword(s):  
Mechanical Properties ◽  
Yield Point ◽  
Experimental Research ◽  
Failure Modes ◽  
Shear Failure ◽  
Short Columns ◽  
Eccentric Compression ◽  
Bending Failure ◽  
Overall Bending ◽  
Compressive Tests

By means of axial compressive and eccentric compressive tests of four Four-tube Concrete-filled Steel Tubular Laced Columns, to research the mechanical properties and failure modes of this structural without yield point. Research shows that, the failure modes of this model, as well as axial compressive short columns, have the same trend of oblique shear failure, and presenting overall bending failure under eccentric compression. The linear eccentricity takes a biggish influence on mechanical properties of laced columns.

scholarly journals Categorization of Failures in Polymer Rapid Tools Used for Injection Molding

Processes ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 17 ◽  
Author(s):  
Anurag Bagalkot ◽  
Dirk Pons ◽  
Digby Symons ◽  
Don Clucas
Keyword(s):  
Injection Molding ◽  
Tool Life ◽  
Failure Modes ◽  
Shear Failure ◽  
Cost Effective ◽  
Critical Parameters ◽  
Cost Effective Method ◽  
Edge Failure ◽  
Underlying Mechanisms ◽  
Bending Failure

Background—Polymer rapid tooling (PRT) inserts for injection molding (IM) are a cost-effective method for prototyping and low-volume manufacturing. However, PRT inserts lack the robustness of steel inserts, leading to progressive deterioration and failure. This causes quality issues and reduced part numbers. Approach—Case studies were performed on PRT inserts, and different failures were observed over the life of the tool. Parts molded from the tool were examined to further understand the failures, and root causes were identified. Findings—Critical parameters affecting the tool life, and the effect of these parameters on different areas of tool are identified. A categorization of the different failure modes and the underlying mechanisms are presented. The main failure modes are: surface deterioration; surface scalding; avulsion; shear failure; bending failure; edge failure. The failure modes influence each other, and they may be connected in cascade sequences. Originality—The original contributions of this work are the identification of the failure modes and their relationships with the root causes. Suggestions are given for prolonging tool life via design practices and molding parameters.

scholarly journals Failure Analysis of Glulam Lumber Beam Made from Meranti Lumber Pieces (Shorea SP)

2020 ◽  
Vol 22 (2) ◽  
pp. 137-145
Author(s):  
Ali Murtopo ◽  
Ria Miftakhul Jannah ◽  
Sabilla Sabilla ◽  
Labibah Tsaniyah
Keyword(s):  
Tensile Strength ◽  
Failure Modes ◽  
Shear Failure ◽  
Standard Specimen ◽  
Full Length ◽  
Research Needs ◽  
Cross Sectional ◽  
Mode Design ◽  
Cross Sectional Size ◽  
Limited Length

The development of glue-laminated (glulam) lumber beam gives many good results. Meranti (Shorea SP) is one of the construction lumber that can be used as glulam to optimize its use. The limitation of the glulam lumber beam is the limited length of the lumber, so it must be joined to get a certain length. The lumber available in the market on average has a limited size and cross-sectional length. The larger the cross-sectional size and length of the lumber make the higher the price. Used lumber and residual lumber also have many weaknesses, such as the length of suitable lumber is too short, lumber defects, and lumber damages. Further research needs to be done to optimize the use of new, used, and residual meranti lumber through the use of lumber pieces as a glulam lumber beam maker. Standard specimen and test based on ASTM D-198. Glulam lumber beam is made from pieces of meranti lumber planks of certain length which are arranged into lamina beam with the size of 5.5x9.5x150 cm3. Variations in the length of the pieces of meranti lumber planks for making glulam lumber beam, among others, 40 cm, 50 cm, 60 cm, 50 cm with full length lowest layer and 150 cm (full length). The adhesive used is polyurethane glue. The span between supports is 130 cm. The beam is tested for center point loading. The analysis results show that the joints on the outermost layer that receive tensile stress of the glulam lumber beam can cause weakening in the beam because the tensile strength of the adhesive is weaker than the tensile strength of lumber. Failure at the tensile joint of the outer layer of the beam can trigger a shear failure mode. Design of joints should not be placed on layers that are subject to tensile stresses so as not to trigger shear failure modes so that the strength of the glulam lumber beam can be optimal.

Novel cellular perlite–epoxy foams: Effect of density on mechanical properties

2016 ◽  
Vol 53 (4) ◽  
pp. 425-442 ◽  
Author(s):  
Haleh Allameh-Haery ◽  
Erich Kisi ◽  
Thomas Fiedler
Keyword(s):  
Elastic Modulus ◽  
Failure Modes ◽  
Shear Failure ◽  
Volume Fraction ◽  
Volcanic Glass ◽  
Effective Elastic Modulus ◽  
High Volume ◽  
Density Range ◽  
Longitudinal Splitting ◽  
Closed Cell

A novel type of economical lightweight foam with density from 0.15 to 0.45 g/cm3 was made from a high volume fraction of expanded volcanic glass (perlite) in an epoxy matrix. The compressive strength, effective elastic modulus, and modulus of toughness of the foams all increased with the foam density. The strength increased linearly, peaking at 1.7 MPa whereas the effective elastic modulus and modulus of toughness increased at parabolically increasing and decreasing rates, respectively. The specific compressive stress of the newly developed foam in the density range of 0.3–0.44 g/cm3 is comparable with foams made from alumina, aluminium–silicon carbide, closed cell phenolic resin, and closed cell polypropylene. Post-test SEM observations coupled with photogrammetry during the tests revealed three different failure modes: longitudinal splitting, shear failure, and compression failure were present over the whole density range. The material was found to be a good candidate for the stiffening cores within sandwich panels.

Non-dimensional pressure–impulse diagrams for blast-loaded reinforced concrete beam columns referred to different failure modes

2018 ◽  
Vol 21 (14) ◽  
pp. 2114-2129 ◽  
Author(s):  
Runqing Yu ◽  
Diandian Zhang ◽  
Li Chen ◽  
Haichun Yan
Keyword(s):  
Reinforced Concrete ◽  
Dynamic Response ◽  
Concrete Beam ◽  
Failure Modes ◽  
Shear Failure ◽  
Reinforced Concrete Beam ◽  
Pressure Impulse ◽  
Beam Columns ◽  
Concrete Beam Columns ◽  
Bending Failure

The pressure–impulse diagram is commonly used to assess the damage level of structural components under explosion. Non-dimensional pressure–impulse diagrams referred to different failure modes was obtained using a new methodology in this article. Nine non-dimensional key parameters were first proposed on basis of the Euler beam theory. Considering the shear failure, an elastic–plastic method to calculate the dynamic response of reinforced concrete beam columns was then proposed for different failure modes. Three failure categories, for example, bending failure, shear failure, and combined shear and bending failure, were considered. The threshold between the three failure modes was determined using non-dimensional pressure–impulse curves. A systematic parametric study was conducted to investigate the effects of different non-dimensional parameters on the dynamic response and the failure modes of reinforced concrete beam column. Parametric study shows that the nine non-dimensional key parameters are sufficient to calculate the dynamic response of reinforced concrete beam columns. Moreover, present study shows that the tangent modulus of direct shear stress–slip relation has a great influence on the failure modes. Beam columns with a smaller tangent modulus are more likely to generate combined shear and bending failure mode.

scholarly journals Dynamic Response and Failure Mechanism of Layered Thin Plate Rock Mass Under Sustained Dynamic Load

2021 ◽  
Author(s):  
Feng Li ◽  
Chuang Chen ◽  
Yue Zhang ◽  
Xin Zhao ◽  
Xinhui Dong ◽  
...  
Keyword(s):  
Rock Mass ◽  
Thin Plate ◽  
Dynamic Load ◽  
Failure Modes ◽  
Shear Failure ◽  
Maximum Shear Stress ◽  
Central Axis ◽  
Dynamic Loads ◽  
Vibration Modes ◽  
Short Side

Abstract Based on the dual equation of Hamilton system and Duhamel's integral, and the orthogonality of the deflection equations, the mechanical model of homogeneous rectangular thin plate rock mass was established. And the results showed that the effective vibration modes of thin plate granite with four sides fixed were the 1st, 5th and 6th orders under uniform dynamic load, and their vibration frequencies were 310rad/s, 975rad/s and 1309rad/s respectively. Under sustained dynamic load, moreover, the change of the vibration state of the 1st mode was the most sharp, and the positive and negative alternation of its amplitude was the most frequent in the whole period, which had the most obvious effect on the vibration of the thin plate rock mass. Based on the Fourier transform formula, the Fourier series expressions and waveforms of sustained dynamic loads which contained rectangular wave, triangular wave and impact wave were obtained. The vibration characteristics of thin plate rock mass under these three kinds of sustained dynamic loads, the dynamic distribution of deflection, stress and maximum shear stress, as well as the dynamic damage and failure modes were all obtained. The results showed that plate cracks occurred firstly in the middle of the four sides and these cracks would propagate rapidly along the boundary of the thin plate rock mass; and then, plate cracks occurred at the central of the thin plate and the main develop tendency of these cracks was outward along the long central axis, moreover, these cracks also tended to expand outward along the short side central axis. It could be concluded that the initial failure position of the thin plate rock mass could be determined by the 1st effective mode, and the development direction and trend of the damage could be determined by 5th and 6th effective vibration modes; under sustained dynamic load, tensile-shear failure occurred at four sides and shear failure at four corners; The tensile failure occurred in the central area of the thin plate, which developed into a main crack along the central long axis and a secondary crack along the short central axis, forming an " O-十" fracture pattern.

scholarly journals Study on Flexural Behavior of Cross-Laminated Timber Based on Different Tree Species

2019 ◽  
Vol 2019 ◽  
pp. 1-8
Author(s):  
Weidong Lu ◽  
Jiahui Gu ◽  
Bibo Wang
Keyword(s):  
Bearing Capacity ◽  
Failure Modes ◽  
Shear Failure ◽  
Flexural Behavior ◽  
Calculation Formula ◽  
Poplar Wood ◽  
Test Results ◽  
Cross Laminated Timber ◽  
Number Of Layers ◽  
Bending Failure

The flexural behavior of CLT panels was experimentally studied. The effects of number of layers, thickness and wood combination on the failure modes, ultimate bearing capacity, stiffness, and ductility of the specimen were analyzed. The test results showed that the flexural strength of the hybrid CLT specimens was basically unchanged, but the stiffness increased by 8% to 22% compared with the CLT specimens of all poplar wood. Compared with the CLT of the whole Douglas fir, the failure mode of the hybrid specimens changes from brittle shear failure to ductile bending failure. Furthermore, the calculation formula of the bending bearing capacity under various failure modes was proposed. The analytical results agreed well with the test results.

scholarly journals Cracking failure of curved hollow tree trunks

2020 ◽  
Vol 7 (3) ◽  
pp. 200203
Author(s):  
Yan-San Huang ◽  
Pei-Lin Chiang ◽  
Ying-Chuan Kao ◽  
Fu-Lan Hsu ◽  
Jia-Yang Juang
Keyword(s):  
Tensile Strength ◽  
Material Properties ◽  
Tree Species ◽  
Orthotropic Material ◽  
Failure Modes ◽  
Tensile Force ◽  
Bending Moment ◽  
Initial Curvature ◽  
Bending Failure ◽  
Hollow Tree

Understanding the failure modes of curved hollow tree trunks is essential from both safety and conservation perspectives. Despite extensive research, the underlying mechanism that determines the cracking failure of curved hollow tree trunks remains unclear due to the lack of theoretical analysis that considers both the initial curvature and orthotropic material properties. Here we derive new mathematical expressions for predicting the bending moment, M crack , at which the cracking failure occurs. The failure mode of a tree species is then determined, as a function of t / R and cR , by comparing M crack with M bend , where t , R and c are, respectively, the trunk wall thickness, outer radius and initial curvature; M bend is the bending moment for conventional bending failure. Our equation shows that M crack is proportional to the tangential tensile strength of wood σ T , increases with t / R , and decreases with the final cR . We analyse 11 tree species and find that hardwoods are more likely to fail in conventional bending, whereas softwoods tend to break due to cracking. This is due to the softwoods' much smaller tangential tensile strength, as observed from the data of 66 hardwoods and 43 softwoods. For larger cR , cracking failure is easier to occur in curvature-decreasing bending than curvature-increasing due to additional normal tensile force F acting on the neutral cross-section; on the other hand, for smaller cR , bending failure is easier to occur due to decreased final curvature. Our formulae are applicable to other natural and man-made curved hollow beams with orthotropic material properties. Our findings provide insights for those managing trees in urban situations and those managing for conservation of hollow-dependent fauna in both urban and rural settings.

Finite Element Simulation on Three-point Bending of Brazed Aluminum Honeycomb Panel

2010 ◽  
Vol 168-170 ◽  
pp. 1046-1050 ◽  
Author(s):  
Ming Jun Peng ◽  
Yong Sun ◽  
Ji Yao ◽  
Yong Hua Duan ◽  
Sai Bei Wang
Keyword(s):  
Failure Modes ◽  
Shear Failure ◽  
Failure Load ◽  
Honeycomb Core ◽  
Three Point Bending ◽  
Aluminum Honeycomb ◽  
Longitudinal Bending ◽  
Panel Thickness ◽  
Bending Failure ◽  
Honeycomb Panel

The mechanics behaviors on three-point bending of brazed aluminum honeycomb panel by FEM are investigated in this paper. The results show that honeycomb panel have three typical failure modes under bending load：failure of honeycomb core collapse, the whole panel bending failure and face sheet shear failure. Honeycomb lateral bending failure load is greater than the longitudinal bending failure load. When the ratio of honeycomb core thickness and panel thickness is between 10% to 15%, the strongest cellular panel bending occurs.

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