Average Deformations Research Articles

A stacking sequence optimization strategy for process‐induced deformation of multi‐layer thick asymmetric laminates

AbstractThe occurrence of process‐induced deformations of composites laminates is challenging for assembly accuracy and may lead to a service life reduction of parts. However, it can be obviously mitigated through different optimization strategies on the basis of the accurate curing process simulation. In this study, a stacking sequence optimization strategy is proposed and applied to multi‐layer thick asymmetric laminates. The shapes of deformed laminate plates are experimentally investigated in virtue of the three‐dimensional coordinate measuring machine. The thermo‐chemical–mechanical behaviors of plates are first verified through the comparisons of model predicted and experimental process‐induced deformations. Then the nonlinear control formula achieved through the regression model is proposed for the direct relationship between stacking sequences and process‐induced deformations. Finally, the required solutions are generated by solving the control formula. With the comparisons between the average deformations before and after optimizations, it is found that the magnitudes of deformations are significantly reduced, especially when the unoptimizated deformations are large.Highlights The thermo‐chemical–mechanical behavior can be described in the curing process simulation model. The deformed shapes of multi‐layer thick asymmetric laminate plates are measured by a three‐dimensional coordinate measuring machine. The stacking sequence optimization strategy is implemented by introducing a nonlinear control formula.

Characteristics of Damage to Brown Rice Kernels under Single and Continuous Mechanical Compression Conditions.

During the rice milling process, single and continuous compression occurs between brown rice and the processing parts. When the external load exceeds the yield limit of brown rice, brown rice kernels are damaged; with an increase in compression deformation or the extent of compression, the amount of damage to the kernels expands and accumulates, ultimately leading to the fracture and breakage of kernels. In order to investigate the mechanical compression damage characteristics of brown rice kernels under real-world working conditions, this study constructs an elastic-plastic compression model and a continuous damage model of brown rice kernels based on Hertz theory and continuous damage theory; the accuracy of this model is verified through experiments, and the relevant processing critical parameters are calculated. In this study, three varieties of brown rice kernels are taken as the research object, and mechanical compression tests are carried out using a texture apparatus; finally, the test data are analysed and calculated by combining them with the theoretical model to obtain the relevant critical parameters of damage. The results of the single compression crushing test of brown rice kernels showed that the maximum destructive forces Fc in the single compression of Hunan Early indica 45, Hunan Glutinous 28, and Southern Japonica 518 kernels were 134.77 ± 11.20 N, 115.64 ± 4.35 N, and 115.84 ± 5.89 N, respectively; the maximum crushing deformations αc in the single compression crushing test were 0.51 ± 0.04 mm, 0.43 ± 0.01 mm, and 0.48 ± 0.17 mm, respectively; and the critical average deformations αs of elasticity-plasticity deformation were 0.224 mm, 0.267 mm, and 0.280 mm, respectively. The results of the continuous compression crushing test of brown rice kernels showed that the critical deformations αd of successive compression damage formation were 0.224 mm, 0.267 mm, and 0.280 mm, and the deformation ratios δ of compression damage were 12.24%, 14.35%, and 12.84%. From the test results, it can be seen that the continuous application of compression load does not result in the crushing of kernels if the compression deformation is less than αd during mechanical compression. The continuous application of compressive loads can lead to fragmentation of the kernels if the compressive deformation exceeds αd; the larger the compression variant, the less compression is required for crushing. If the compression deformation exceeds αc, then a single compressive load can directly fragment the kernels. Therefore, the load employed during rice milling should be based on the variety of brown rice used in order to prevent brown rice deformation, which should be less than αd, and the maximum load should not exceed Fc. The results of this study provide a theoretical reference for the structure and parameter optimisation of a rice milling machine.

Calculation of the stress-strain state of layers of cross-ply laminate based on an experimental stress-strain curves under uniaxial tension

A method for calculating the stress-strain state of layers of cross-ply laminate based on an experimental deformation diagram under uniaxial tension is proposed. The essence of the method consists in solving a system of two equations describing the experimental curves σx = f(εx) and σx = f(εy), which allows determination of two unknown parameters related to the secant elastic characteristics of the material layers. The law of change in the remaining unknown parameters is set by assumptions regarding deformation of the polymer matrix composite and its layers during loading. To carry out the calculation, it is necessary to set the initial values of the elastic properties of the unidirectional material of the layers, which should be well consistent with the initial values of the elastic properties of the structure under study determined from the experiment. According to the developed algorithm, calculated dependences between average stresses, deformations and secant elastic properties of the layers of the structure are obtained (0°/90°/90°/0°) made of fiberglass E-Glass/MY750 using experimental data from the literature. Calculations carried out for three sets of initial values of the elastic properties of the material under study showed qualitatively identical results. The transverse tensile stress in the 90° layer reaches a maximum in the first half of the stress-strain diagram, and then decreases to zero. A similar stress in the 0° layer reaches a maximum at the failure point of the structure under study. It is revealed that the maximum calculated values of transverse stresses acting in layers 0° and 90° noticeably exceed the transverse tensile strength of the material specified in the literature. The longitudinal tensile stress in the 0° layer reaches a maximum at the failure point and corresponds to 95% of the value of the longitudinal tensile strength of the material. The longitudinal compressive stress in the 90° layer is at a low level throughout the deformation process of the structure under study. The results of this study can be recommended for developing models of the behavior of layers with cracks in the matrix when loading a polymer matrix composite.

Estimating the Strength and Deformation Properties of the End Milling Process Using Numerical Analysis Methods

In the study, the end mill made of titanium material and having a unique design with a 4-flute was simulated during the milling of the workpiece with a geometry of a rectangular prism made of aluminum material. Ansys Explicit Dynamics was used in the study. Modeling and simulation of the milling process were made with finite element analysis for the estimation of the strength properties. The end mill is chosen as a titanium alloy, while the milled workpiece is aluminum. All parameters were kept constant and only the depth of cut was examined in three scenarios 3, 6, and 9 mm. The simulations were carried out by taking the spindle speed of 4000 RPM and the feeding rate of 3350 mm/s. One of the conveniences provided by Explicit Dynamics is that it can be solved in very small time intervals, and for this reason, the time step in the analysis is solved by taking 0.001 seconds. While hexahedral mesh is applied to the tool, a tetrahedral mesh is applied to the workpiece. The generated mesh has 8,012 nodes and 17,052 mesh elements. Average deformations for both tool and workpiece are 36.92, 38.10, and 38.29 mm, respectively. Strain also shows a similar trend to the total deformation and the average values for all three scenarios were found to be 2.84 x 10-3, 4.43 x 10-3 and 3.99 x 10-3 mm/mm. Also, the stress values were obtained as 78.23, 76.83, and 77.99 MPa.

Probabilistic evaluation of plan quality for time-dependent anatomical deformations in head and neck cancer patients

PurposeIn addition to patient set-up uncertainties, anatomical deformations, e.g., weight loss, lead to time-dependent differences between the planned and delivered dose in a radiotherapy course that currently cannot easily be predicted. The aim of this study was to create time-varying prediction models to describe both the average and residual anatomical deformations. MethodsWeekly population-based principal component analysis models were generated from on-treatment cone-beam CT scans (CBCTs) of 30 head and neck cancer patients, with additional data of 35 patients used as a validation cohort. We simulated treatment courses accounting for a) anatomical deformations, b) set-up uncertainties and c) a combination of both. The dosimetric effects of the simulated deformations were compared to a direct dose accumulation based on deformable registration of the CBCT data. ResultsSet-up uncertainties were seen to have a larger effect on the organ at risk (OAR) doses than anatomical deformations for all OARs except the larynx and the primary CTV. Distributions from simulation results were in good agreement with those of the accumulated dose. ConclusionsWe present a novel method of modelling time-varying organ deformations in head and neck cancer. The effect on the OAR doses from these deformations are smaller than the effect of set-up uncertainties for most OARs. These models can, for instance, be used to predict which patients could benefit from adaptive radiotherapy, prior to commencing treatment.

FLEXIBLE INTRAMEDULLARY NAILS IN PEDIATRIC SUBTROCHANTERIC FEMUR FRACTURE: BIOMECHANICAL STUDY.

Evaluate the stability provided by two flexible intramedullary nails (FINs) in a simulation of fractures at the proximal levels in pediatric femur models. Two FINs were inserted in 18 synthetic models of pediatric femurs. Fractures were simulated at one of three levels, and the models were divided into the following groups (n=6): diaphysis (control), subtrochanteric and trochanteric. Flex-compression tests were performed with force up to 85 N. Relative stiffness and the average deformation was obtained. Torsion tests were performed by rotating the proximal fragment until 20°, to obtain the average torque. At flex-compression, the set's average relative stiffness and average deformations were: 54.360x103 N/m and 1.645 mm in the control group, respectively. In the subtrochanteric group, the relative stiffness was 31.415x103 N/m (-42.2%) and the deformation was 2.424 mm (+47.3%) (p<0.05). For the trochanteric group, the relative stiffness was 30.912x103 N/m (+43.1%) and the deformation was 2.508 mm (+52.4%) (p<0.05). In torsion, the average torque was 1.410 Nm in the control group; 1.116 Nm in the subtrochanteric group (-20.8%), and 2.194 Nm in the trochanteric group (+55.6%) (p<0.05). FINs do not seem to be biomechanically competent for the treatment of proximal femoral fractures. Level of Evidence I; Therapeutic Studies - Investigating the results of treatment.

Continuum description of confluent tissues with spatial heterogeneous activity.

A continuum description is built to characterize the stationary and transient deformations of confluent tissues subject to heterogeneous activities. By defining a coarse-grained texture matrix field to represent the shape and size of cells, we derive the coarse-grained stress tensor for the vertex model. Activity in the tissue takes the form of inhomogeneous apical contractions, which can be modeled as reductions of the vertex model reference areas or perimeters representing activity in the medial and perimeter regions of the cells, respectively. For medial activity, the extra stress is just an isotropic pressure, while for perimeter activity, it also has a deviatoric component, which is aligned with the texture matrix. The predictions of the continuum description are compared with the average spatiotemporal deformations obtained in simulations of the vertex model subject to localized apical contractions, showing an excellent agreement, even if the active patch is as small as one cell. The fluctuations around the average are more prominent when the activity is in the medial region due to the lack of negative active shape feedback, which, coupled with the confluent property, increases cellular shape and size variations.

Analysing functional implications of differences in left ventricular morphology using statistical shape modelling

Functional implications of left ventricular (LV) morphological characterization in congenital heart disease are not widely explored. This study qualitatively and quantitatively assessed LV shape associations with a) LV function and b) thoracic aortic morphology in patients with aortic coarctation (CoA) with/without bicuspid aortic valve (BAV), and healthy controls. A statistical shape modelling framework was employed to analyse three-dimensional (3D) LV shapes from cardiac magnetic resonance (CMR) data in isolated CoA (n = 25), CoA + BAV (n = 30), isolated BAV (n = 30), and healthy controls (n = 25). Average 3D templates and deformations were computed. Correlations between shape data and CMR-derived morphometric parameters (i.e., sphericity, conicity) or global and apical strain values were assessed to elucidate possible functional implications. The relationship between LV shape features and arch architecture was also explored. The LV template was shorter and more spherical in CoA patients. Sphericity was overall associated with global and apical radial (p = 0.001, R2 = 0.09; p < 0.0001, R2 = 0.17) and circumferential strain (p = 0.001, R2 = 0.10; p = 0.04, R2 = 0.04), irrespective of the presence of aortic stenosis and/or regurgitation and controlling for age and hypertension status. LV strain was not associated with arch architecture. Differences in LV morphology were observed between CoA and BAV patients. Increasing LV sphericity was associated with reduced strain, independent of aortic arch architecture and functional aortic valve disease.

Left ventricular morphology in patients with aortic coarctation and bicuspid aortic valve: novel insights from a statistical shape modelling framework

Abstract Background The functional implications of left ventricular (LV) morphological characterization in congenital heart disease (CHD) are not widely explored. Purpose This study qualitatively and quantitatively assessed LV shape associations with a) LV function and b) thoracic aortic morphology in patients with aortic coarctation (CoA) with/without bicuspid aortic valve (BAV). Methods A statistical shape modelling (SSM) framework was employed to analyse three-dimensional (3D) LV shapes from cardiac magnetic resonance (CMR) imaging data in n=110 cases including: isolated CoA (n=25), CoA+BAV (n=30), isolated BAV (n=30), and age-matched healthy controls (n=25). Average 3D templates (Picture 1) and deformations were computed. Correlations between shape data and CMR-derived morphometric parameters (i.e. sphericity, conicity) as well as CMR-derived global and apical strain values were assessed to elucidate possible functional implications. The relationship between LV shape features and arch architecture (i.e. gothicity, tortuosity) was also explored by means of regression analysis. Results The LV template was shorter and more spherical in CoA patient (Picture 1), as also confirmed by statistical analysis of the SSM-derived shape modes. LV sphericity, which was higher in CoA, was associated (p≤0.04) with lower global longitudinal, radial and circumferential strain, irrespective of the presence of aortic stenosis and/or regurgitation. Conversely, neither LV morphology nor LV strain was not associated with arch architecture. Conclusions Differences in LV morphology were observed between CoA and BAV patients. Increasing LV sphericity was associated with reduced strain, independent of aortic arch architecture and functional aortic valve disease. Funding Acknowledgement Type of funding sources: Foundation. Main funding source(s): British Heart Foundation and NIHR BRC

A generalised Newmark method with displacement hardening for the prediction of seismically induced permanent deformations of diaphragm walls

This paper presents a generalised Newmark method (GNM) incorporating a displacement hardening mechanism for the prediction of permanent displacements accumulated by diaphragm walls during earthquakes. A key feature of the proposed approach is the adoption of an evolution law for the critical acceleration, which links its current value to the accumulated wall permanent displacements. This displacement hardening mechanism is based on a simplified relation between the average plastic shear deformations experienced by the passive zone of soil below dredge level and the mobilised soil friction angle. This relation is determined indirectly by the evolution of the passive earth-pressure coefficient with wall displacement/rotation, as obtained in quasi-static model wall experiments. The proposed approach has been validated by comparing its predictions with the experimental data obtained in centrifuge model tests of cantilevered and propped walls. In spite of the simplifying assumptions on which it is based, the GNM has demonstrated that it is capable of capturing the essential features of the retaining structures’ kinematics and provides realistic predictions of permanent wall displacements.

ANALYSIS OF TEST EQUIPMENT FOR INVESTIGATION OF MATERIALS UNDER A STRONG LOAD APPLICATION

An analysis of publications on this topic. It is established that in most literature sources the work of wood is shown only in the ascending branch of deformation, which is a false statement. The method of experimental studies of alder and spruce wood by axial compression along the fibers with a short-term load at standard humidity (by increasing displacements) is presented. The age of the wood was about 40 years. Experimental studies of such samples were performed on a modern STM- 100 test machine. 18 samples with a cross section of 30x30x120 mm were tested. Based on the experiment, complete deformation diagrams “stress σc - strain uc” were constructed and the main parameters were established: critical and residual strains, as well as their corresponding stresses. It is established that both diagrams have an ascending and descending branch, ie they work in both pre-critical and super-critical stages of work.&#x0D; The average critical deformations of alder wood uc,0,d = 0,00397, as well as the corresponding maximum stresses fc,0,d = 35,6 MPa, and spruce wood - uc,0,d = 0,00421 (fc,0,d = 38.1 MPa).&#x0D; Also, the average residual deformations for alder wood uc,fin = 0.277, and the corresponding stresses σc,fin = 3.9 MPa; for spruce wood uc,fin = 0.212, and stress - σc,fin = 3.6 MPa. &#x0D; It is confirmed that deciduous and coniferous wood at standard humidity has an ascending and descending branch, ie works in the subcritical and supercritical stages of work.&#x0D; In the future it is necessary to conduct such experimental studies for other deciduous and coniferous species. In the future, determined mechanical characteristics experimentally, it is necessary to propose methods for finding and theoretical, which will give a complete picture of such materials.

Effects of residual stress and equivalent bending stiffness on the dimensional stability of the thin-walled parts

The monolithic thin-walled parts are widely used in the aeronautic and astronautic field because of its excellent mechanical performance and light weight, but the thin-walled parts are vulnerable to the machining deformation due to its low stiffness and high material removal rate. According to the relative basic theory, the stiffness and internal residual stress of the part are the critical factors affecting the dimensional stability. In this work, the influences of equivalent bending stiffness and residual stress on the dimensional stability of thin-walled parts are studied. Nine typical thin-walled parts in three groups with two materials (7075 aluminum alloy for A1 ~ A3 and B1 ~ B3, and Ti6Al4V titanium alloy for B4 ~ B6) are machined and treated with different processes. Topology optimization technique is used to optimize the structure of parts to enhance the bending stiffness. Corresponding finite element method (FEM) simulations are carried out to further investigate the generation mechanism. The deformations in 312 h after machining are measured using coordinate measuring machine, and the deformation changes of the parts are obtained and analyzed. Finally, based on topological optimization and stress relief technology, a machining deformation control method for the monolithic thin-walled parts is proposed. Results show that the maximum and average deformations of thin-walled are evidently decreased using the proposed method.

Taguchi Optimization of Roundness and Concentricity of a Plastic Injection Molded Barrel of a Telecentric Lens.

Plastic is an attractive material for the fabrication of tubular optical instruments due to its light weight, high strength, and ease of processing. However, for plastic components fabricated using the injection molding technique, roundness and concentricity remain an important concern. For example, in the case of a telecentric lens, concentricity errors of the lens barrel result in optical aberrations due to the deviation of the light path, while roundness errors cause radial stress due to the mismatch of the lens geometry during assembly. Accordingly, the present study applies the Taguchi design methodology to determine the optimal injection molding parameters which simultaneously minimize both the overall roundness and the overall concentricity of the optical barrel. The results show that the geometrical errors of the optical barrel are determined mainly by the melt temperature, the packing pressure, and the cooling time. The results also show that the optimal processing parameters reduce the average volume shrinkage rate (from 4.409% to 3.465%) and the average deformations from (0.592 mm to 0.469 mm) of the optical barrel, and the corresponding standard deviation values are reduced from 1.528% to 1.297% and from 0.263 mm to 0.211 mm, respectively. In addition, the overall roundness and overall concentricity of the barrel in the four planes are positively correlated.

Seismic performance evaluation of a precast concrete structure with deformation-based limit criterions

In precast reinforced concrete buildings, which constitute an important part of the industrial buildings in Turkey, the force flow between the structural elements is provided by beam-column connections with or without transferring moments. In general, moment resisting beam-column connections with mechanical or emulative components are applied at the mezzanine level. For precast concrete structures, strength-based design is the most common design approach in engineering practice. In recent years, performance based seismic design and evaluation approach also gained attention which provides numerical estimation of the damage in structural elements subjected to earthquake loading. This study presents the performance based seismic assessment of a two-story precast building based on the seismic evaluation requirements of Turkish Building Earthquake Code 2018. For this purpose, numerical simulation model has been established by using lumped plasticity models for connections and distributed plasticity models for columns. Strong ground motion records are scaled based on TBEC-2018 acceleration spectrum for a specific location, and nonlinear time history analyses are performed in x and y directions simultaneously. The performance evaluation results using average deformations show that there is a significant difference between plastic rotation and reinforcing bar strain performance limits.

Seismic Slope Displacement of Tailings Dam: A Comparative Study between Modified Newmark and Mohr-Coulomb Models

ABSTRACT Modified Newmark method is proposed including the equivalent seismic loading and critical acceleration dependant on the dynamically exerted plastic yielding and tension cutoff effects along the base of the sliding mass. The fully nonlinear FE analysis is based on elasto-plastic Mohr-Coulomb material model. The proposed algorithm was validated in an example of 72 m high tailings dam. The Newmark permanent displacements were compared with the average plastic deformations resulting from the nonlinear Mohr-Coulomb model. The comparison shows satisfactory agreement for low to moderate nonlinear slope behavior. For deep nonlinearity, the modified Newmark method can be used as a decision-making tool only.

Permissible Values of the Dynamic Impact of the Rolling Stock on the Railway Track in the Case of Axle Load Increase

Purpose. The study is aimed at determining experimentally the values of the parameters characterizing the dynamic effect of rolling stock on the railway track, substantiating the maximum permissible (limiting) values. Methodology. To investigate the interaction between the track and the rolling stock, the devices to record various physical processes were installed on the experimental sections. The devices were installed in 8 sections along the outer railway line. To establish the actual state of the track, field measurements were carried out in accordance with the Program and research methodology. Findings. According to the results of experimental tests of the impact on the track, it was revealed that the average vertical loads, and, accordingly, the average vertical deformations, under the cars with an axle load of up to 25 tf/axle are higher than that under the cars with an axle load of up to 23.5 tf/axle by 8 percent. The maximum vertical loads under the cars with an axle load of 25 tf/axle exceeded the average loads by 10.0 tf, and under the cars with an axle load of up to 23.5 tf/axle exceeded the average values by 12.8 tf. During the tests, no cars were found in which the vertical dynamic force exceeds 20 tf, and the horizontal force exceeds 10 tf. Therefore, the norms of permissible dynamic impact can be taken in accordance with the Regulations on Preventive Maintenance and Repair Track Work on the Railways of Ukraine. Originality. The authors conducted a study to assess the dynamic characteristics of the interaction of track and rolling stock, in particular the stresses in the edges of the rail base, vertical and horizontal forces from the wheels of rolling stock. Practical value. On the basis of the results obtained, it is possible to estimate the permissible values of the dynamic effect of the rolling stock on the railway track to substantiate the need to change the standards for the material consumption of the track superstructure and labor. In turn, this will make it possible to plan the repair and track periods more economically and according to the actual indicators of the state of the track superstructure.

МОМЕНТЫ В ЖЕЛЕЗОБЕТОННЫХ КОНСТРУКЦИЯХ ПРИ ИЗГИБЕ С КРУЧЕНИЕМ

The moments in reinforced concrete during bending with torsion were determined, the new first hypothesis of linear deformations and its filling of the diagram during bending with torsion for the analytical second functional as a function of three functions - an exponent, a straight line and a parabola curve. A simple new method is found (from the family of mesh methods) and a summed function of additional deplanation is proposed. The new second hypothesis of angular deformations and its filling of the diagram in reinforced concrete during bending with torsion is constructed. The analytical first general undefined functional is a function of functions, as well as transitions, operations between functions. At the same time, a spatial triple integral of arguments from longitudinal deformations for the first hypothesis was obtained, as well as the third and fourth functionals (indefinite and definite) from moments (bending and twisting) with the projection of the coefficients of the diagram of "deformations - stresses" of compressed concrete and the filling coefficients of the diagrams of compressed concrete for their shoulders to the neutral axis for a field of small squares. The bending and torque moments from the compressed area of concrete and working reinforcement are determined (folded for their levels or expanded into algebraic functions from the synthesis of the computational model of reinforced concrete blocks). In this case, we have new functionals (from the first to the fourth functional), proposed hypotheses (first and second), as well as cross sections (from small squares) to a spatial crack. There are also jumps (cracks) lateral, normal, etc., from the first - third stage of average deformations of concrete and working reinforcement.

GENERAL FUNDAMENTALS OF REINFORCED CONCRETE ELEMENTS AND STRUCTURES DEFORMATION MECHANICS

This article presents a critical development analysis of the general deformation theory and models of reinforced concrete elements and structures resistance to force effects. Their relationship with the defining provisions of the mechanics of reinforced concrete elements and structures deformation is estimated. The main disadvantages of the considered models are established. General provisions of the mechanics of reinforced concrete elements and structures deformation are proposed to be developed on the basis of a universal deformation-force model. It is noted that the latter is devoid of most of the shortcomings characteristic to other models. The main advantage of the deformation-force model is indicated, associated with the expansion of the well-known system of static, geometric and physical relationships to the level of statically definable. It becomes especially noticeable when calculating reinforced concrete elements and structures for deflections and crack resistance. One of the main features of the deformation-force model is emphasized, which makes it possible to quite simply «embed» or integrate the technical theory of reinforcement to concrete adhesion into the general theory of reinforced concrete deformation. Through the averaged design section and average deformations of materials in the block between adjacent cracks, all parameters of the normal cracks formation and opening in the deformation-force model are directly related to the parameters of reinforcement to concrete adhesion.The effectiveness of using the deformation-force model of reinforced concrete to force effects resistance was evaluated by a statistical comparison of theoretical calculations with the reinforced concrete elements experimental studies results tested by different authors. Similar comparisons were made for the methods of the current standards. It was confirmed that the priority in the accuracy of assessing the reinforced concrete elements stress-strain state parameters belongs to the calculation method, which is based on the deformation-force model of reinforced concrete resistance.

Fluence of age factor on main strength and deformative properties of timber

The analysis of literature sources on this topic is carried out. It was found that the influence of age on the main strength and deformation parameters has not been studied. The method of experimental researches of coniferous and deciduous species of solid wood of different age at one-time short-term loading along fibers is resulted. To solve the problems, a series of samples of 1 sort of solid wood in the form of prisms with a cross section of 30x30x120 mm were made. The following species of wood were tested: coniferous species - larch, pine, spruce; deciduous - birch, alder, ash. The age of wood was 20, 40, 60 years. At the time of testing, the moisture was 12%. The humidity of the wood was controlled using a moisture meter MD-814. Experimental studies were performed on a servo-hydraulic test machine STM-100 under a rigid load regime (by increasing the displacements of the press plate of the test machine). Based on the obtained results, complete diagrams of deformation of deciduous (birch, alder, ash) and coniferous (larch, pine, spruce) species of solid wood at different ages (60, 40, 20 years) were constructed. The number of twin samples that were tested was 126 pieces. The main strength and deformation parameters were determined experimentally, in particular the average critical deformations of all studied wood species and the corresponding average maximum stresses. It is established that in the case of a rigid test regime, the deformation diagram of solid wood necessarily has two branches - ascending and descending. That is, the samples work in the so-called supercritical stage of work. It was found that the age of wood directly affects the strength and deformability of solid wood. In particular, with increasing age from 20 to 60 years, the strength and deformability of deciduous and coniferous species of solid wood increases significantly. Based on the test results, conclusions were drawn. Further research on this topic is highlighted.

SQUARE GRID DEFORMATION ANALYSIS OF THE MACULA AND POSTOPERATIVE METAMORPHOPSIA AFTER MACULAR HOLE SURGERY.

To investigate the correlation between postoperative metamorphopsia and macular deformation after macular hole surgery. This study included 28 eyes of 28 patients who underwent vitrectomy and internal limiting membrane removal for an idiopathic macular hole. The retinal vasculatures were compared between preoperative and postoperative photographs, and postoperative deformation of the macula was assessed as deformation of the square grid. The displacement of each node was measured, and deformation of the grid was calculated as differences in the coordinates of the adjacent nodes. These parameters were analyzed to find correlation with metamorphopsia measured using the M-charts after 6 postoperative months. The average deformations in the vertical and horizontal lines of the grid were 94.29 μm and 49.72 μm, respectively. Perifoveal deformation was significantly greater than parafoveal deformation (P = 0.001∼0.019). The multiple regression analysis demonstrated that the vertical M-score correlated with superior perifoveal deformation of the vertical line on the fovea (P = 0.036), and the horizontal M-score correlated with temporal perifoveal deformation of the horizontal line on the fovea (P = 0.032). The parafoveal tissue was displaced with the fovea concurrently after internal limiting membrane removal in macular hole surgery causing perifoveal deformation, which correlated with postoperative metamorphopsia.