scholarly journals How does bark contribution to postural control change during tree ontogeny? A study of six Amazonian tree species

2020 ◽  
Vol 71 (9) ◽  
pp. 2641-2649
Author(s):  
Romain Lehnebach ◽  
Tancrède Alméras ◽  
Bruno Clair
Keyword(s):  
Tensile Stress ◽  
Compressive Stress ◽  
Residual Strain ◽  
Tree Species ◽  
Bark Thickness ◽  
Relative Thickness ◽  
Allometric Relationship ◽  
Stem Size ◽  
Control Change ◽  
Bark Anatomy

Abstract Recent works revealed that bark is able to produce mechanical stress to control the orientation of young tilted stems. Here we report how the potential performance of this function changes with stem size in six Amazonian species with contrasted bark anatomy. The potential performance of the mechanism depends both on the magnitude of bark stress and the relative thickness of the bark. We measured bark longitudinal residual strain and density, and the allometric relationship between bark thickness and stem radius over a gradient of tree sizes. Constant tensile stress was found in species that rely on bark for the control of stem orientation in young stages. Other species had increasing compressive stress, associated with increasing density attributed to the development of sclereids. Compressive stress was also associated with low relative bark thickness. The relative thickness of bark decreased with size in all species, suggesting that a reorientation mechanism based on bark progressively performs less well as the tree grows. However, greater relative thickness was observed in species with more tensile stress, thereby evidencing that this reduction in performance is mitigated in species that rely on bark for reorientation.

scholarly journals Stress–strain relationship model of glulam bamboo under axial loading

2020 ◽  
Vol 29 ◽  
pp. 2633366X2095872
Author(s):  
Yang Wei ◽  
Mengqian Zhou ◽  
Kunpeng Zhao ◽  
Kang Zhao ◽  
Guofen Li
Keyword(s):  
Tensile Stress ◽  
Compressive Stress ◽  
Failure Modes ◽  
Axial Loading ◽  
Tensile Failure ◽  
Stress Strain ◽  
Laminated Bamboo ◽  
Bamboo Scrimber ◽  
Strain Relationship ◽  
Strain Model

Glulam bamboo has been preliminarily explored for use as a structural building material, and its stress–strain model under axial loading has a fundamental role in the analysis of bamboo components. To study the tension and compression behaviour of glulam bamboo, the bamboo scrimber and laminated bamboo as two kinds of typical glulam bamboo materials were tested under axial loading. Their mechanical behaviour and failure modes were investigated. The results showed that the bamboo scrimber and laminated bamboo have similar failure modes. For tensile failure, bamboo fibres were ruptured with sawtooth failure surfaces shown as brittle failure; for compression failure, the two modes of compression are buckling and compression shear failure. The stress–strain relationship curves of the bamboo scrimber and laminated bamboo are also similar. The tensile stress–strain curves showed a linear relationship, and the compressive stress–strain curves can be divided into three stages: elastic, elastoplastic and post-yield. Based on the test results, the stress–strain model was proposed for glulam bamboo, in which a linear equation was used to describe the tensile stress–strain relationship and the Richard–Abbott model was employed to model the compressive stress–strain relationship. A comparison with the experimental results shows that the predicted results are in good agreement with the experimental curves.

scholarly journals Bark Characteristics of Scots Pine Logs

2020 ◽  
Vol 3 (1) ◽  
pp. 66
Author(s):  
Ferréol Berendt ◽  
Erik Pegel ◽  
Lubomir Blasko ◽  
Tobias Cremer
Keyword(s):  
Scots Pine ◽  
Tree Species ◽  
Waste Product ◽  
Mean Value ◽  
Bark Thickness ◽  
Water Displacement ◽  
Federal States ◽  
Bark Damage ◽  
Great Relevance ◽  
High Degree

The wood of Scots pine (Pinus sylvestris L.) shows good properties as building and construction timber but also as furniture or pulp and paper, and thus, is one of the most commercially important European tree species. Scots pine are mostly harvested and processed with a high degree of mechanization. In Northeast Germany (federal states of Brandenburg and Berlin), 36% of harvested Scots pine have a diameter at breast height (DBH) between 7 and 19.9 cm. As a typical industrial wood assortment, a large proportion of the resulting small-sized logs are used in the wood industry to produce boards. Although bark is considered a by-product or waste product of the industry, no actual study has quantified the bark thickness, bark volume, bark mass and bark damage of such Scots pine logs. Therefore, the bark characteristics from 50 logs from 10 different piles were analyzed. Bark volume was quantified using the water displacement method, bark mass by weighing, bark thickness with a precision caliper and bark damage by tape measurements. The diameters of the analyzed 150 log discs were normally distributed and the mean value was 12.9 cm. The results showed average bark damages from 12.0%, which were mostly caused during the felling and processing of logs with the harvester. No significant correlation was found between double bark thickness (mean: 3.0 mm) and the diameter; whereas fresh bark volume (mean: 5.6%) and dry bark mass (mean: 3.3%) were significantly affected by the diameter. As shown for spruce by other authors, bark characteristics may change over time and therefore, should be measured regularly. Moreover, it was shown that bark parameters are site dependent. Thus, quantifying bark characteristics for economically important tree species at both the local and national scale is of great relevance. More detailed analyzes are described by Berendt et al. (2021) [1].

scholarly journals Long-Term Behaviour of Precast Concrete Deck Using Longitudinal Prestressed Tendons in Composite I-Girder Bridges

2018 ◽  
Vol 8 (12) ◽  
pp. 2598 ◽  
Author(s):  
Haiying Ma ◽  
Xuefei Shi ◽  
Yin Zhang
Keyword(s):  
Tensile Stress ◽  
Compressive Stress ◽  
Precast Concrete ◽  
Concrete Strength ◽  
Steel Girders ◽  
Concrete Creep ◽  
Compressive Stresses ◽  
Girder Bridge ◽  
Concrete Deck

Twin-I girder bridge systems composite with precast concrete deck have advantages including construction simplification and improved concrete strength compared with traditional multi-I girder bridge systems with cast-in-place concrete deck. But the cracking is still a big issue at interior support for continuous span bridges using twin-I girders. To reduce cracks occurrence in the hogging regions subject to negative moments and to guarantee the durability of bridges, the most essential way is to reduce the tensile stress of concrete deck within the hogging regions. In this paper, the prestressed tendons are arranged to prestress the precast concrete deck before it is connected with the steel girders. In this way, the initial compressive stress induced by the prestressed tendons in the concrete deck within the hogging region is much higher than that in regular concrete deck without prestressed tendons. A finite element analysis is developed to study the long-term behaviour of prestressed concrete deck for a twin-I girder bridge. The results show that the prestressed tendons induce large compressive stresses in the concrete deck but the compressive stresses are reduced due to concrete creep. The final compressive stresses in the concrete deck are about half of the initial compressive stresses. Additionally, parametric study is conducted to find the effect to the long-term behaviour of concrete deck including girder depth, deck size, prestressing stress and additional imposed load. The results show that the prestressing compressive stress in precast concrete deck is transferred to steel girders due to concrete creep. The prestressed forces transfer between the concrete deck and steel girder cause the loss of compressive stresses in precast concrete deck. The prestressed tendons can introduce some compressive stress in the concrete deck to overcome the tensile stress induced by the live load but the force transfer due to concrete creep needs be considered. The concrete creep makes the compressive stress loss and the force redistribution in the hogging regions, which should be considered in the design the twin-I girder bridge composite with prestressed precast concrete deck.

Stress Analysis and Microstructure Evolution of Titanium Alloy Pipe during Flattening Processing

2019 ◽  
Vol 944 ◽  
pp. 1088-1093
Author(s):  
Jun Chen ◽  
She Wei Xin ◽  
Wei Zhou ◽  
Qian Li ◽  
Si Yuan Zhang ◽  
...  
Keyword(s):  
Titanium Alloy ◽  
Tensile Stress ◽  
Compressive Stress ◽  
Outer Layer ◽  
Contact Stage ◽  
Straight Wall ◽  
Vertical Part ◽  
Left And Right ◽  
Titanium Alloy Tube ◽  
Flattening Process

TA24 titanium alloy pipe with 638mm diameter and 19mm wall thickness is carried out continuous load flatten test, and the stress of internal and external pipe wall during flatten process is studied in this paper. The results show that the TA24 titanium alloy tube has good flattening performance, and the flattening process has experienced original stage, flattened oblate stage, flattened straight wall stage, flattened depressed stage, flattened concave contact stage. During the flattening process, the outer layer of the upper and lower wall of the tube is subjected to compressive stress, and the inner layer material is subjected to tensile stress. The tensile and compressive forces cause the vertical part of the upper and lower walls to be concave. The outer layer of the left and right circular arc parts is subjected to tensile stress and the inner layer is subjected to tensile stress. The compressive stress also causes the radius of the arc to decrease due to the combined force of the tensile and compressive forces, that is, the flattening occurs. With the decrease of and pressing distance under continuous loading condition, the metal on the left and right sides of the pipe gathers toward the middle depression, which aggravates the deformation of the upper and lower walls until the upper and lower walls contact, and the arc radius of the left and right walls decreases until the outer surface cracks. The pipe microstructure changes significantly into elongated deformation structure during the flattening process. The most severe part of the deformation is the left and right end arc of the pipe, followed by the upper and lower end depression.

An approach to reduce stress and defects: a hybrid process of laser cladding deposition and shot peening

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Xiaoyu Zhang ◽  
Dichen Li ◽  
Jiale Geng
Keyword(s):  
Tensile Stress ◽  
Compressive Stress ◽  
Laser Cladding ◽  
Shot Peening ◽  
Hybrid Process ◽  
Layer By Layer ◽  
Residual Tensile Stress ◽  
Forming Process ◽  
Content Type ◽  
Thermal Forming

Purpose Laser cladding deposition is limited in industrial application by the micro-defects and residual tensile stress for the thermal forming process, leading to lower fatigue strength compared with that of the forging. The purpose of this paper is to develop an approach to reduce stress and defects. Design/methodology/approach A hybrid process of laser cladding deposition and shot peening is presented to transform surface strengthening technology to the overall strengthening technology through layer-by-layer forming and achieve enhancement. Findings The results show that the surface stress of the sample formed by the hybrid process changed from tensile stress to compressive stress, and the surface compressive stress introduced could reach more than four times the surface tensile stress of the laser cladding sample. At the same time, internal micro-defects such as pores were reduced. The porosity of the sample formed by the hybrid process was reduced by 90.12% than that of the laser cladding sample, and the surface roughness was reduced by 43.16%. Originality/value The authors believe that the hybrid process proposed in this paper can significantly expand the potential application of laser cladding deposition by solving its limitations, promoting its efficiency and applicability in practical cases.

Simultaneous effects of reintroduction strategy and seed size on the initial development of two tropical tree species in an abandoned eucalyptus plantation

2020 ◽  
Vol 68 (6) ◽  
pp. 439
Author(s):  
Julie Christine Scaloppi ◽  
Andréa Lúcia Teixeira de Souza
Keyword(s):  
Seed Size ◽  
Tree Species ◽  
Survival Rates ◽  
Plant Size ◽  
Plant Performance ◽  
Initial Development ◽  
Eucalyptus Plantation ◽  
Hymenaea Courbaril ◽  
Stem Size ◽  
Direct Sowing

Seedling planting is the most common strategy used to reintroduce tropical native tree species; however, direct sowing has simplicity and operational ease advantages. Functional traits such as seed size and growth rates have been shown to be relevant for better plant performance. We evaluated the effects of intraspecific variation in seed size and the reintroduction strategy simultaneously on the development of Hymenaea courbaril (L.) and Enterolobium timbouva (Mart.) introduced in an abandoned eucalyptus plantation over 462 days. Plants from small, medium and large seeds were reintroduced by planting seedlings and direct seeding. Both species achieved high rates of emergence and survival was high in the two reintroduction strategies. Seed size was not related to emergence and mean time to emergence for either species. The survival of both species was higher than 74% in the field, and seed size had little effect on survival rates. In general, H. courbaril plants introduced by direct sowing had higher growth, and seed size correlated positively with stem size. In contrast, the growth of E. timbouva plants introduced by seedling planting was higher than in plants introduced by direct sowing regardless of seed size. The light requirements of this species seem higher than for H. courbaril. Our results suggest the feasibility of reintroducing species by direct sowing in eucalyptus understory, but since plant growth varies between species, there may be a balance between the advantage of the initial plant size provided by planting seedlings and the advantage of a better root development provided by direct sowing.

Understorey–canopy affinities in boreal forest vegetation

1981 ◽  
Vol 59 (9) ◽  
pp. 1709-1716 ◽  
Author(s):  
T. J. Carleton ◽  
P. F. Maycock
Keyword(s):  
Boreal Forest ◽  
Relative Density ◽  
Forest Fire ◽  
Tree Species ◽  
Nutrient Status ◽  
James Bay ◽  
Apparent Lack ◽  
Stem Size ◽  
Single Tree ◽  
Natural Combination

One hundred and ninety-seven boreal forest stands, in a region of Ontario and Quebec south of James Bay, were examined. Tree species were summarized as relative density of each of five stem size classes. These data formed the basis for an exclusive polythetic divisive stand classification into 10 groups. Most of these groups were characterized by a single tree species. The affinity of each of 410 understorey taxa was assessed with respect to each canopy stand group or natural combination of groups. Only 121 understorey taxa showed specificity to the canopy classes identified. This apparent lack of tight overstorey–understorey affinity is discussed in relation to site nutrient status and regeneration following forest fire.

Thermal and Thermomechanical Phenomena in Picosecond Laser Copper Interaction

2004 ◽  
Vol 126 (3) ◽  
pp. 355-364 ◽  
Author(s):  
Xinwei Wang
Keyword(s):  
Tensile Stress ◽  
Compressive Stress ◽  
Structural Damage ◽  
Temperature Drop ◽  
Picosecond Laser ◽  
Liquid Interface ◽  
Back Side ◽  
Laser Materials ◽  
Solid Liquid Interface ◽  
Solid Liquid

Thermal and thermomechanical phenomena in laser metal interaction are of great importance in terms of understanding the underlying mechanisms in laser materials processing, optimizing the efficiency of laser micro-machining, and minimizing laser induced damage. In this work, Molecular Dynamics (MD) simulation is carried out to investigate picosecond laser copper interaction. A method has been developed to account for the laser beam absorption in, and the thermal transport sustained by, free electrons. Superheating is observed, and an evident temperature drop is revealed at the solid-liquid interface, which moves at a speed of 4400 m/s. However, the later phase change from solid to liquid happens in the target simultaneously and no visible movement of solid-liquid interface is observed. The results show that the laser induced stress wave consists of a strong compressive stress and a weak tensile stress. After reflection at the back side of the MD domain, the strong compressive stress becomes a strong tensile stress, which results in a visible drop of the number density of atoms. In the presence of this strong tensile stress, voids have formed in the region near the back side of the MD domain, indicating that the strong tensile stress in laser materials interaction plays an important role in terms of inducing structural damage.

Lateral grain growth in poly-Si films by gas flame high temperature annealing

1996 ◽  
Vol 441 ◽  
Author(s):  
W. F. Qu ◽  
A. Kitagawa ◽  
Y. Masaki ◽  
M. Suzuki
Keyword(s):  
High Temperature ◽  
Tensile Stress ◽  
Compressive Stress ◽  
Grain Growth ◽  
Strain Energy ◽  
Driving Forces ◽  
Stress Distributions ◽  
High Temperature Annealing ◽  
Gas Flame ◽  
Si Films

AbstractPoly-Si films with the preferential orientation to a random, a (100) and a (110) texture were annealed using a flat gas flame. Remarkable lateral grain growth of (111) grains was observed for poly-Si films with a random and a (110) texture, while in (100) texture films the growth of (100) grains predominated over other grains. There existed tensile stress in as-prepared films. Grains with different orientation were under a different tensile stresses, and such stress distributions on the orientation of grains were different for different textures. The tensile stress was found to become larger in grown grains after high temperature annealing, while the stress on shrunken grains decreased or turned to compressive stress after annealing. These results indicate that strain energy stored in grains is one of the important driving forces in secondary grain growth.

Mechanical Behavior of Segmented Lining Structure of Tunnel under Acting Ground Fractures in Xi’an Zone

2011 ◽  
Vol 261-263 ◽  
pp. 1778-1783
Author(s):  
Sheng Jun Shao ◽  
Fang Tao She ◽  
Juan Fang
Keyword(s):  
Tensile Stress ◽  
Mechanical Behavior ◽  
Compressive Stress ◽  
Three Dimensional ◽  
Vertical Displacement ◽  
Maximum Tensile Stress ◽  
Internal Force ◽  
Subway Tunnel ◽  
Lining Structure ◽  
Pass Through

Xi’an ground fracture, caused by the extraction of groundwater and the movement of fault under soil strata, is a geo-hazard. The movement of ground fracture originates the uneven settlement of upward block and downward block. In Xi’an ground fracture region, the segmented lining structure was adopted in subway tunnel to pass through the ground fracture, so as to adapt for the uneven settlement. Three-dimensional elastic-plastic finite difference method was applied to simulate the initial lining structure, second segmented lining structure, surrounding soils and ground fracture. The horizontal and vertical displacement of segmented lining structure, surrounding soils pressure and internal force of segmented lining structure in subway tunnel were analyzed by the calculation results. The knowledge on mechanical behavior of segmented lining structure passing through an active ground fracture and surrounding soils was shown as following. The relative vertical displacement between segmented lining structure sects beside the ground fracture increases remarkably with the movement of ground fracture, and the segmented lining structure located in upward displaceent block near ground fracture originates notable rotary. Tension or compression deformation occured in the deformation joint between adjacent segmented lining structures near the ground fracture.There was a significant change in the contact pressure of the first sect of lining structure in the upward displace block. Under the same uniform settlement at the bottom of upward diaplacement block, the relativly vertical displacemtn on the surfaceof ground fracture strata without tunnel equals 50cm, but the relativly vertical displacement between adjacent segmented lining structure at ground fracture is 18.2cm on the design level of arch top of lining strcutre. the maximum tensile stress of segmented lining structure is 2.02MPa, the maximum compressive stress of segmented lining is 3.49MPa. In conclusion, segmented lining structure can adapts to the uneven settlement caused by the movement of ground fracture. Though maximum tensile and compressive stress of sengmented lining structure passing through the active ground fracture is bigger than the general lining structure located in soils strata without the ground fracture, the segmented lining structure constructed by the steel fibre concrete can bear with the maximum tensile stress.

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