Stem Deflection Research Articles

Exploring the influence of flexural rigidity variability of aquatic plants on stem deflection geometry and flow characteristics

The existing assumption of a constant flexural rigidity (EI) for the entire height of aquatic plants in the analysis of flow past flexible vegetation may not translate in to real scenario as EI of a flexible plant stem varies along the height due to variation in tissue structure and cross section. This variation is therefore needed to be effectively quantified for better analysis of flow-vegetation interaction. In this regard, the own-weight cantilever method was used to represent the variability of EI along the stem height of three plants: water lily, water chestnut, and lotus. Analytical models are proposed to predict stem deflection geometry and vertical velocity distribution across channel depth incorporating EI as a function of stem height. Analytical and experimental data, obtained from open-channel flume tests, significantly support the developed models and confirm the assumption of variable flexural rigidity. Further investigations show that the flexural rigidity, transcends being a mere constant numeric value; it profoundly influences various aspects of the fluid-vegetation interaction such as: the extent of deflection geometry, velocity reduction, Reynold stress variation, and penetration length. Therefore, this study is crucial for better understanding of the physics of sediment transport, pollutant mixing, and wetland management and restoration.

Analytical justifications of constructive parameters of bionic colters for vertical soil treatment

Bionic coulters imitate natural forms and functions, which help reduce energy costs for soil tillage. The aim of the research was to justify the design and structural parameters of turbo discs (coulters) for vertical tillage based on the principles of bionic reverse engineering. Using this method, an equation for the shape of the turbo discs (coulters) was derived, which was obtained by approximating the shell of the argonaut (Argonauta argo). The equation takes into account the main structural parameters of the turbo discs: diameter Dd, cutout height Hm, wave height Hw, number of cutouts n, and spiral coefficient k. As a result of analytical studies on the interaction process between a solid disc and plant residues, the optimal diameter value was determined to be Dd=460 mm under the condition of submerging stems with a thickness of 10-20 mm to a depth of 80 mm. The analytical studies confirmed that the presence of cutouts on the disc prevents stem deflection and ensures better stem capture. In analysing the obtained dependencies using the Wolfram Cloud software package, the optimal values for the cutouts were determined: cutout height Hm=40 mm, number of cutouts n=8. The presence of waves on the disc surface ensures that the interaction with plant residues is independent of their position on the field surface and creates conditions for vertical soil tillage. It was found that, to minimize specific cutting resistance and maximize the degree of soil fragmentation, the optimal wave parameters for the coulter are a wave height of Hw=24.4 mm. The justified parameters of the coulters provide the best balance between soil fragmentation efficiency and reduction in energy consumption for soil tillage. The obtained results can be used to adapt existing agricultural machinery to the new structural parameters of coulters to improve its efficiency.

Response of gerbera under soil and soil-less production systems

Response of gerbera var. Arka Nesara was studied under different soil-less production systems with the aim to improve quality, productivity and water use efficiency, in completely randomized design with eight treatments viz., deep flow technique (DFT), nutrient film technique (NFT), aggregate wick system (AWS) with pots on NFT bench, AWS with pots on ground, AWS with grow bags on ground, AWS on soil bed, aeroponics and conventional soil-based drip system, which were replicated five times. Results revealed that AWS with pots on ground recorded maximum plant height (31.66 cm), leaf length (21.31 cm), leaf breadth (9.96 cm) and stalk diameter near neck (4.75 mm), minimum stem deviation (1.27 cm) and stem deflection (2.2o), prolonged vase life (9.2 days), greater water use efficiency (92 mL/plant/day) and water saving (83.46%). Hence, cultivation of gerbera var. Arka Nesara under aggregate wick system with pots on ground could be the superior alternative for traditional soil cultivation.

The effect of stem and root-plate defects on the tree response during static loading—Numerical analysis

Despite continual development of the tree pulling test, there is no systematic study on the interaction of stem and root-plate stiffness in relation to tree assessment results. New methods involving numerical modelling and optical techniques provide tools for effective and deeper understanding of the interaction of stem and root-plate stiffness. Within this study, a finite element (FE) model of the tree response to static loading was developed, and the interaction between the stem and root-plate stiffness was analysed on three levels: longitudinal stem strains, root-plate inclinations and stem deflection curve. The model was validated at all three levels by comparison with experiment. Sensitivity analysis of the validated model showed a significant correlation of root-plate stiffness represented by the root volume and soil elastic modulus to the tree response. By analysing the defects in tree response, the importance of proper location for detection of strains and inclinations was demonstrated, especially regarding asymmetrical defects. A numerical estimate of the second derivative of displacement based on the Taylor approximation, was used to analyse the stem deflection curve.

Analysis of deflection and dynamic plant characteristics of Cyperus malaccensis Lam

ABSTRACT In this study, flexural rigidity, natural frequency, and damping coefficient of Cyperus malaccensis Lam. with long stems were measured for application for fluid–structure interaction simulation in a field. Numerical solutions of deflection and natural frequency were calculated by ANSYS with finite element method (FEM). The triangular cross-section shape of C. malaccensis stem has a big neighbourhood of the root and the cross-section has taper structure to become small towards tip direction. Two numerical simulation models for FEM have Model A with a triangular prism shape and Model B with a truncated trigonal pyramidal shape to evaluate the effects of stem tapering. Because of large C. malaccensis stem deflection, an equation for nonlinear deflection was introduced to solve a problem regarding flexural rigidity. Natural frequencies of the stem were estimated using amplitude ratio during stem swinging by forced vibration, captured using a high-speed camera. The Model B corresponded with the measurement, and the results suggested that the stem characteristics were affected by cross-section shape. Damping coefficient was calculated using free vibration response, which was consistent with the analytical solution and numerical data calculated using measured characteristics. Abbreviations C. malaccensis: Cyperus malaccensis; FEM: finite element method; GIAHS: Globally Important Agricultural Heritage System

THE EFFECT OF SILICON ON MORPHOLOGICAL TRAITS AND MECHANICAL PROPERTIES OF Polygonatum multiflorum (L.) All. ‘VARIEGATUM’ CUT SHOOTS

Garden perennials are a source of floristry material produced in field or under covers. A perennial producing long, leafy shoots, which in flower arrangements might successfully substitute fern or palm leaves, is Polygonatum multiflorum. The variety characterizing with decorative white margined leaves is ‘Variegatum’. To improve their quality, the growth stimulator Actisil Hydro Plus, which contains 0.6% of active silicon in a form of orthosilicic acid was applied. The aim of the conducted experiment was to estimate the influence of silicon and a place of cultivation (tunnel and open field) on post-harvest quality determined with morphological features, vase life longevity and mechanical properties of Polygonatum multiflorum (L.) All. ‘Variegatum’ stems. The plants were sprayed with water solutions of Actisil in concentrations: 0.2%, 0.3%, and 0.4%, six times during the growing season in weekly intervals, starting from the first decade of May, always in the morning. It was stated that cultivation of Polygonatum in the unheated foil tunnel increases quality of shoots for cut greenery, determined with morphological features and post-harvest longevity. Cultivation of Polygonatum in a foil tunnel and spraying plants with Actisil in concentrations of 0.3 or 0.4% is advantageous due to possibility to increase a number of shoots from 20% to over 31%, their length from 9% to 11% and fresh weight from 52% to 71%, in comparison to control plants. It is advised to treat plants cultivated in a tunnel, with Actisil in concentration of 0.4% as it improved shoots quality evaluated with their diameter and lower leaves blade area. Spraying plants with Actisil in concentrations of 0.2–0.4% in the tunnel and 0.2% in field prolongs post-harvest shoots longevity by 3–4 days. Plants cultivated in the tunnel characterize with higher strength of shoots determined with higher maximum force causing permanent damage and lower stem deflection than plants cultivated in field. Plants grown in a tunnel and sprayed with Actisil in concentrations of 0.4% characterized with the strongest shoots after 14 days of storage, however a similar effect was observed with the concentration of 0.3% and in case of plants cultivated in field and sprayed with 0.4% of Actisil.

In situ drag coefficient measurements for rooftop trees

To evaluate the drag coefficients for roof-top tree crowns, previously developed field test methods for monitoring wind speed, wind direction, and stem deflection were improved using solar cells as a source of power. A field test was conducted for a Norway spruce and a shirakanba located on a rooftop. The drag coefficients showed large variations during low wind speeds, which were caused by the flexural vibration of the tree trunk due to the fluctuating wind speed. To compensate for this effect, the upper percentage of drag coefficients obtained for the 0.5 m/s wind speed classes were used for the exponential regression for drag coefficient as a function of wind speed. As a result, a conservative evaluation of drag coefficients for a greater range of wind speeds could be established instead of using all data. The drag coefficients at 30 m/s wind speed were estimated to be 0.594 for the Norway spruce, and 0.154 for the shirakanba using the upper 50 % of the data. The exponential function convergence was more gradual for the spruce than for the shirakanba, which may be affected by a difference in the streamlining behavior.

Numerical modeling of free surface flow over submerged and highly flexible vegetation

Vegetation in rivers, estuaries and coastal areas is often submerged and highly flexible. The study of its interaction with the ambient flow environment is important for the determination of the discharge capacity, morphological characteristics and ecological conditions of the water course where it grows. In this work the hydrodynamics of submerged flexible vegetation with or without foliage is investigated by using a 3D numerical model. Flexible vegetation is modeled by momentum sink terms, with the velocity-dependent stem height determined by a large deflection analysis which is more accurate than the previously used small deflection analysis. The effect of foliage on flow resistance is expressed in terms of the change in the product of the drag coefficient and the projected area, which is supported by available experimental data. The computed results show that the vertical profiles of the mean horizontal velocity and the vertical Reynolds shear stress are correctly simulated. The temporal variation of the stem deflection follows closely that of the velocity and the ‘Honami’ phenomenon can be reproduced. The numerical simulations also confirm that the flexibility of vegetation decreases both the vegetation-induced flow resistance force and the vertical Reynolds shear stress, while the presence of foliage further enhances these reduction effects.

Evaluation of drag coefficients of poplar-tree crowns by a field test method

To estimate the wind force that causes windthrow damage to a tree, the drag coefficients of actual-sized trees were evaluated by a field test method. In this method, wind velocity and stem deflection were monitored simultaneously. The wind force acting on a tree crown was calculated from stem deflection; stem stiffness was evaluated by conducting tree-bending tests. The results of tests conducted on three poplar trees showed that drag coefficient decreased with an increase in wind velocity. Although the variation in the drag coefficient was large at low wind velocity because of the vibrating behavior of the stem subjected to variable wind force, the variation at wind velocities above 10 m/s was small. The average drag coefficient at a wind velocity of 30 m/s was estimated by the curve-fitting of a power function to the wind velocity-drag coefficient relationship to be 0.102, which was smaller than that of actual-sized conifers studied in previous wind tunnel experiments. The drag coefficients of these crown areas in the defoliation season were smaller than those measured in the leafy season.

Anchorage of mature conifers: resistive turning moment, root-soil plate geometry and root growth orientation

Eighty-four mature Norway spruce (Picea abies L. Karst), silver fir (Abies alba Mill) and Scots pine (Pinus sylvestris L.) trees were winched over to determine the maximum resistive turning moment (M(a)) of the root-soil system, the root-soil plate geometry, the azimuthal orientation of root growth, and the occurrence of root rot. The calculation of M(a), based on digital image tracking of stem deflection, accounted not only for the force application and its changing geometry, but also for the weight of the overhanging tree, representing up to 42% of M(a). Root rot reduced M(a) significantly and was detected in 25% of the Norway spruce and 5% of the silver fir trees. Excluding trees with root rot, differences in M(a) between species were small and insignificant. About 75% of the variance in M(a) could be explained by one of the four variables--tree mass, stem mass, stem diameter at breast height squared times tree height, and stem diameter at breast height squared. Among the seven allometric variables assessed above ground, stem diameter at breast height best described the root-soil plate dimensions, but the correlations were weak and the differences between species were insignificant. The shape of the root-soil plate was well described by a depth-dependent taper model with an elliptical cross section. Roots displayed a preferred azimuthal orientation of growth in the axis of prevailing winds, and the direction of frequent weak winds matched the orientation of growth better than that of rare strong winds. The lack of difference in anchorage parameters among species probably reflects the similar belowground growth conditions of the mature trees.

Overturning resistance of western redcedar and western hemlock in mixed-species stands in coastal British Columbia

Specific information about the applied forces that cause trees to fail is required to validate mechanistic models of windthrow in different forest types. Static tree-pulling tests were conducted to examine the overturning resistance of western redcedar ( Thuja plicata Donn ex D. Don) and western hemlock ( Tsuga heterophylla (Raf.) Sarg.) in a mixed species second-growth stand in coastal British Columbia. Although widely used, tree-pulling techniques are not standardized. Data from three inclinometers were used to estimate stem deflection, which was found to increase with tree slenderness. Differing methods of fitting stem curvature had a small effect on estimates of self-loading at failure. The distance of the pivot point from the centre of the stem base increased with tree diameter. Accounting for the correct self-loading at failure produced a small difference in the overall turning moment regressions but did not improve the fit of these regressions. However, this difference increased with tree size and warrants consideration in future tree-pulling tests with large or plate-rooted trees. The stem mass – overturning resistance relationship had the best fit and was not significantly different for these species in spite of their differences in wood density and stem form.

Is it possible to manipulate root anchorage in young trees?

The optimal root system architecture for increased tree anchorage has not yet been determined and in particular, the role of the tap root remains elusive. In Maritime pine (Pinus pinaster Ait.), tap roots may play an important role in anchoring young trees, but in adult trees, their growth is often impeded by the presence of a hard pan layer in the soil and the tap root becomes a minor component of tree anchorage. To understand better the role of the tap root in young trees, we grew cuttings (no tap root present) and seedlings where the tap root had (−) or had not (+) been pruned, in the field for 7 years. The force (F) necessary to deflect the stem sideways was then measured and divided by stem cross-sectional area (CSA), giving a parameter analogous to stress during bending. Root systems were extracted and root architecture and wood mechanical properties (density and longitudinal modulus of elasticity, EL) determined. In seedlings (−) tap roots, new roots had regenerated where the tap root had been pruned, whereas in cuttings, one or two lateral roots had grown downwards and acted as tap roots. Cuttings had significantly less lateral roots than the other treatments, but those near the soil surface were 14% and 23% thicker than plants (+) and (−) tap roots, respectively. Cuttings were smaller than seedlings, but were not relatively less resistant to stem deflection, probably because the thicker lateral roots compensated for their lower number. Apart from stem volume which was greater in trees (+) tap roots, no significant differences with regard to size or any root system variable were found in plants (−) or (+) tap roots. In all treatments, lateral roots were structurally reinforced through extra growth along the direction of the prevailing wind, which also improved tap root anchorage. Predictors of log F/CSA differed depending on treatment: in trees (−) tap roots, a combination of the predictors stem taper and %volume allocated to deep roots was highly regressed with log F/CSA (R2 = 0.83), unlike plants (+) tap roots where the combined predictors of lateral root number and root depth were best regressed with log F/CSA (R2 = 0.80). In cuttings, no clear relationships between log F/CSA and any parameter could be found. Wood density and EL did not differ between roots, but did diminish with increasing distance from the stem in lateral roots. EL was significantly lower in lateral roots from cuttings. Results showed that nursery techniques influence plant development but that the architectural pattern of Maritime pine root systems is stable, developing a sinker root system even when grown from cuttings. Anchorage is affected but the consequences for the long-term are still not known. Numerical modelling may be the only viable method to investigate the function that each root plays in adult tree anchorage.

Root-soil rotation stiffness of Norway spruce (Picea abies (L.) Karst) growing on subalpine forested slopes

Trees bend and break when exposed to external forces such as wind, rockfall, and avalanches. A common simplification when modelling the tree response to these forces is to simplify the system as a clamped beam which means that the stem deflection is related to the stem flexibility only. However, a certain part of the stem deflection originates from rotation of the root-soil plate. In this paper, we investigate this contribution to the overall stem deflection. Norway spruce (Picea abies (L.) Karst) trees were subjected to winching tests to analyse the anchorage mechanics of the tree. The tests were performed at two experimental sites with an average slope of 32 and 34° and one site with a nearly flat ground in subalpine forests near Davos, Switzerland, during the vegetation periods of 2003 and 2004. The trees were pulled downslope with a winch and the applied force, stem base rotation, and the angle of the applied force relative to the stem were recorded. After the tree had fallen over, stem diameter and branch mass were measured for every meter segment. These data were used to model the tree in the finite element software ANSYS®, which was used for calculating the rotational stem base moment as a␣function of stem base rotation. The root-soil rotation stiffness k root was defined as the secant stiffness calculated at 0.5° root-soil plate rotation. Young’s modulus of elasticity E of the stem was iteratively changed until the correct stem rotation was obtained. The best correlation between k root and different tree characteristics was the squared diameter at breast height, DBH2. Not incorporating the normal forces due to weight of the overhanging masses from crown and stem resulted in a maximum underestimation for k root of approximately 14%. Thus, also the acting moment on the stem base will be underestimated causing the safety factor against uprooting to be overestimated.

Wind-induced forces in the near-surface lateral roots of radiata pine

The wind-induced movement within near-surface lateral roots of a radiata pine ( Pinus radiata D. Don) tree were investigated to determine whether relationships exist between the resistive bending moment at the base of a tree and stresses in the near-surface lateral roots. The primary instrumentation consisted of four load cells split between windward and leeward roots, and two extensometers set at right angles to record stem deflection in the x– y plane. All instrument output signals were controlled by a data logger, and triggered at pre-set wind velocities to target data collection during specific storm events. The tree was calibrated by winching to obtain the forces that produced the range of stem deflections measured during storm events. After data collection, the test roots were calibrated in a laboratory to obtain the forces required to produce the wind-induced root deformation. The calibrations gave an estimation of relationships between root and tree movement, and root force and bending moment. A comparison of the forces measured in the leeward and windward roots during a storm event indicated a ratio of between 1:2 and 1:3 as the relative contribution to the strength of root anchorage provided by these roots.

Modulus of Elasticity and Moment of Inertia of Grass Hedge Stems

The ability of grass hedges to remain erect where runoff concentrates is critical to their control of ephemeral gully erosion. Hedge resistance to failure depends on the mechanical properties of its stems. We measured moment of inertia (I), modulus of elasticity (E), yield strength (Y), and the bending angle (V) at the elastic limit of stems of switchgrass (Panicum virgatum L.), vetiver (Vetiveria zizaniodes L.), miscanthus (Miscanthus sinensis Cv. gracillimus), and tall fescue (Festuca arundinacae). The stems were sorted into morphological age groups—vegetative, green internode, and woody internode. Moment of inertia was determined from stem geometry and modulus of elasticity from stem deflection from load increments applied in a cantilever arrangement. Yield strength and bending angle were calculated from the displacement of the stem at the last load increment before the elastic limit was exceeded. Grass internodes had I values between 8 and 272 mm4. Their modulii of elasticity were between 2.6 and 8.5 GPa, similar to certain plastics, but their yield strengths of 7 to 30 MPa were generally lower than those of the same plastics. The bending angle at the elastic limit for all grasses was between 2 and 8°.

Modeling the effect of crown shedding and streamlining on the survival of loblolly pine exposed to acute wind

A simulation model using empirical data was developed to determine the effect of crown shedding and streamlining from stem and branch bending on the survival of mature loblolly pine (Pinustaeda L.) trees exposed to acute wind. Data collected from tree winching experiments were used to derive the forces necessary to cause stem failure. These data, combined with data on the vertical distribution of biomass and frontal surface area of sampled trees and hypothetical within-stand wind profiles, were used to calibrate models of static wind effect. Data collected on crown biomass, stem deflection, and branch bending were employed in the model to conduct a sensitivity analysis of the relative contribution of various crown adjustment mechanisms in preventing stem breakage or windthrow. Compared with the base-line model, which included no crown adjustment mechanisms, crown loss of 25% or greater provided the greatest protection against stem breakage or windthrow from forces generated by a hurricane winds of average strength (165 km/h), followed (in order of greatest to least protection) by stem bending, branch streamlining, and crown loss of 10%. However, at the highest wind velocities modeled (249 km/h), stem bending afforded greater protection against wind-generated mortality than 25% crown loss or branch streamlining, but not more than 50% crown loss. Generally, study trees most susceptible to windthrow were tall with a high center of gravity, large crown weight, and small stem taper.

Testing loblolly pine wind firmness with simulated wind stress

The forces and mechanics related to the wind firmness of 30-year-old loblolly pine (Pinustaeda L.) trees were tested by toppling them with a winch and cable system. The ability of trees to resist toppling, expressed as the critical turning moment, was determined by measuring the force exerted by the winch and the height on the tree where the center of force was exerted. Critical turning moments were closely and positively related to stem taper (R2 = 0.91) and various measures of tree size, including tree weight (R2 = 0.96), stem volume (R2 = 0.94), and cubic diameter at breast height (R2 = 0.93). The flexibility of tree stems, measured by the angle of stem deflection during tree pulling, was negatively related to tree size. Measures of center of gravity, crown:stem ratio, and stem moisture content were not significantly related to critical turning moment. Soil moisture content was only weakly significant and negatively related to critical turning moment. With few exceptions, trees subjected to simulated wind stress treatment resembled southern pines subjected to natural acute wind stress. In both cases, root systems were rarely damaged and stem failure occurred instead of uprooting. However, pulled trees tended to break lower on the stem than wind-broken trees.

Laboratory studies of the dynamic behaviour of grass, straw and polystyrene tube during high-speed cutting

Experiments were conducted to study the behaviour of grass and straw stems when cut by sharp and blunt blades at speeds between 5 and 35 m/s; comparative experiments were done with polystyrene tube. Measurements were made of the force and energy during cutting using a piezoelectric force transducer mounted behind the blade on a rotating disc. Stem deflection modes during cutting were recorded photographically by using high-speed film in a camera with an open shutter and firing flash guns sequentially by electronic control, with delay periods ranging from 3 to 425 μs. The lowest speed for efficient cutting (the critical speed) for grass and polystyrene tube was 25–30 m/s. The minimum cutting energy per unit dry matter content for grass with a sharp blade was 55 mJ/mm 2 based on stem wall area. At speeds below the critical speed there was a large stem deflection before cutting was complete, which resulted in long stubble lengths and high cutting energy (up to 400–500 mJ/mm 2 in grass). There was no evidence of a critical speed, however, when cutting straw. The mean peak force for grass per unit dry matter content was 18 N/mm of stem diameter, which was 2.6 times greater than when cutting straw. When cutting above the critical speed for grass (inertia cutting) cutting times were as low as 0.3 ms for the sharp blade, and the stem deflection during cutting was equal to about three stem diameters. For straw, however, the deflection before cutting was complete, represented 8–10 stem diameters, with times of about 1.0 ms. For inefficient cutting at low speeds (c. 5 m/s), cutting times ranged up to 15 ms with stem deflections at the blade of up to 32 diameters for a cutting height of 40mm. The difference between stubble length and nominal cutting height for inertia cutting was about 2 mm for sharp blades but ranged up to 50 mm for inefficient cuts at low speeds. Grass stems showed the widest range of deflection mode immediately after cutting. This varied from stem translation and rotation at low speeds, (c. 5 m/s) to marked bending at intermediate speeds (15–25 m/s) and inertia cutting, with little stem displacement, at higher speeds (>25 m/s). Straw exhibited marked stem translation and rotation with little bending at speeds below 25 m/s but marked bending at higher speeds. Polystyrene tube showed a marked bending over its length at speeds up to 25 m/s, above which cutting was in the inertial mode. The minimum cutting energy for grass stems was three times that required for quasi-static cutting in shear. At low cutting speeds (<12m/s) about 65% of the energy was utilized in overcoming friction. For straw, however, the frictional component was generally relatively low (5–10%) and stem kinetic energy was equal to about 20% of the total energy input. The specific cutting energy was twice as large for the blunt blade as for the sharp blade in grass and straw. The difference between stubble length and nominal cutting height was generally about three times greater when using the blunt blade.

Laboratory studies of the effect of blade parameters and stem configuration on the dynamics of cutting grass

Laboratory experiments were conducted to study the cutting of grass stems with single blades over a range of cutting speeds from 15 to 35 m/s. The blade rake angle was varied from 0 to 45°, using both sharp and blunt cutting edges, and blade thicknesses of 1 to 3 mm were used in a blunt condition. The effect of stem inclination away from the blade was studied over a range of 0 to 60° and the effect of cutting arrays of stems was examined. The blade force and energy during cutting were measured using a piezoelectric transducer. The stem deflection modes were recorded photographically by the use of a camera with an open shutter and the sequential firing of a series of flash guns using electronic control. Blade rake angle was found to have no significant effect on specific cutting force or energy when cutting above the critical speed. At lower speeds, however, increasing the blade angle resulted in an increasing number of uncut stems. The thickness of blunt blades had no significant effect on critical cutting speed or specific cutting force and energy. The bluntest blade (0–15 mm edge radius) required three times the specific cutting energy and twice the specific peak force as a sharp blade (0–325 mm edge radius). The principal effect of the angle of stem inclination was an increase in critical speed from 25 to 60 m/s, as the angle of inclination increased from 0 to 60°. When cutting groups of stems, the critical speed was not dependent on the configuration and number of stems in the group; the specific cutting energy was independent of the group configuration and equal to that when cutting single stems.

飛び石事故防止のための受刃付き刈払機刈刃の試作

To prevent stone accidents, several modifications have been made to a conventional bush cutter head. One of the modification is to mount a shear bar with counter edges over the conventional blade (counter edge cutting type).Another modification is to put two notched blades, one over the other, and to reciprocally reverse the blade (relative cutting type).Tests were conducted in relation to stone scattering, operation efficiency and energy required to cut stems of weed, and result were compared with impact cutting type bush cutter without counter edges.1) Because the counter edges obstructed stone scattering, the percentage of stones scattered toward the operator by the counter edge cutting type bush cutter was half of that of the impact cutting type.2) The percentage of stones scattered by the counter edge type decreased with the decrease of the blade rotating speed, and the direction of stone scattering tends to shift on the left-hand side of the operator, making it safer to use the counter edge type.3) The work efficiency for the impact cutting type rapidly decreased as the rotating speed of blade decreases to 5, 000rpm or less, where that of the counter edge type decreased a little with the slow rotating speed.4) For the counter edge cutter type, the energy to cut single stems of Golden-rod decreased with the decrease in the blade rotating speed, and with the increase in the blade traveling speed. Impact cutting has been shown to impart energy to the stem due to stem deflection and also to suffer energy loss from stem due to blade friction, Hence, impact cutting type would be expected to require more energy than counter edge type.5) For cutting of young rice plants, the effect of increasing clearance between the blade and counter edge was small over a range of clearance in practice. The young rice plants shearing abilities of the counter edge and relative cutting type were superior to that of the impact cutting type. More than 90% of rice plants were sheared by relative cutting type even at the low level of peripheral speed, 5-15m/s.Since these cutter heads has a complicated structure, it is evident that more work using different approaches is necessary.