85 results about "Bending fatigue" patented technology

The invention discloses a gear pair life prediction method based on dynamic stress, belongs to the technical field of reliability design of mechanical transmission systems, and aims to solve the problem of inaccurate life prediction caused by neglecting a dynamic effect and a real surface topography in an existing gear design method. The method comprises the following steps: firstly, acquiring gear pair interface mechanical property parameters considering shafting vibration, dynamic load and surface roughness, wherein the parameters comprise transient oil film pressure, friction coefficient, oil film thickness and shear stress; solving a three-dimensional subsurface stress field by adopting an algorithm and calculating von Mises equivalent stress distribution; stress volume integration is conducted on different rough surfaces, the honed surface is used as the reference, the relative fatigue life of other surfaces is calculated based on the Zaretsky life prediction theory, and accurate prediction and process optimization of the contact fatigue life are achieved; meanwhile, the dynamic bending stress of the tooth root is calculated based on the dynamic normal load, and the bending fatigue safety coefficient is checked.

This invention relates to a 1900MPa grade ultra-high strength and toughness stainless gear steel and its preparation method. The chemical composition of the 1900MPa grade ultra-high strength and toughness stainless gear steel, by mass percentage, is: C 0.08-0.11%, Cr 10-12%, Ni 2-4%, Mo 2-5%, Co 10-13%, V 0.2-0.6%, Nb 0.02-0.05%, Al 0.5-1.0%, with the balance being Fe and unavoidable impurities. Its composition design must meet the following requirements: Chromium equivalent Cr... eq It is 17~18, with a nickel equivalent (Ni). eq The martensitic transformation point is 14-15. s The temperature range is 240~280℃. Its beneficial effects are: strengthening through the composite precipitation of intermetallic compounds NiAl and M₂C carbides, combined with Cr... eq Ni eq M s A synergistic design incorporating 5%–10% metastable austenite achieves an excellent balance between strength and toughness. The resulting steel exhibits tensile strength ≥1900 MPa, yield strength ≥1550 MPa, elongation ≥13%, fracture toughness ≥80 MPa·m¹ / ², and bending fatigue limit reaching 920 MPa. It is particularly suitable for manufacturing critical structural components requiring high load-bearing capacity and high reliability, such as aircraft engines, and has broad application prospects.

The application discloses a prediction method for the relationship between welding repair defects and fatigue life of TC17 titanium alloy blades, and comprises the following steps: step one, establishing a fatigue life prediction model related to repair defects; step two, preparing a rotary bending fatigue sample; step three, heat treating a surfacing sample; step four, processing the rotary bending fatigue sample; step five, testing the rotary bending fatigue; step six, analyzing a fracture and counting defects; and step seven, establishing a rotary bending fatigue life prediction model. The application selects an electric arc welding wire repair test block, tests the rotary bending fatigue performance of the test block, observes and counts the defect morphology, size and position of the fracture, analyzes the corresponding relationship between the defects and the fatigue life, establishes a fatigue life prediction model related to the repair defects, and determines the influence of the pore defects on the fatigue life of the repaired blade through the model.

The invention discloses a method for evaluating the low-temperature fatigue performance of an asphalt mixture, belongs to the technical field of road engineering, and aims to solve the technical problem of how to more accurately and comprehensively evaluate the fatigue performance of the asphalt mixture in a low-temperature environment. According to the technical scheme, the method comprises the following steps: preparing a prismoid test piece and a beam test piece made of the same asphalt mixture as the prismoid test piece; acquiring a temperature change sequence of the pavement structure in the target test environment for a plurality of continuous hours through temperature acquisition equipment; taking the collected temperature change sequence as an environment control condition, carrying out a constraint test piece temperature stress test on the prismoid test piece, and synchronously recording the axial force per hour in the test process; calculating the average temperature stress value in the test period according to the axial force per hour and the size of the prism test piece; the average temperature stress value serves as the initial stress level of the four-point bending fatigue life test and is pre-loaded on the beam test piece, and a plurality of different load stress levels are selected for testing.

A blended rope is provided having an outer sheath (8) enclosing at least a strength member (7), the strength member (7) having high-strength synthetic fibers, the strength member (7) being a blended strength member (7) formed with a combination of ARAMID fibers and HMPE fibers, the blended strength member comprising a non-homogeneous distribution of the ARAMID and HMPE fibers, wherein the weight ratio of ARAMID to HMPE in the strength member (7) is preferably a minimum of 80:20.

A wave-shaped web I-beam front axle, including I-beam and the front axle body arranged at both ends of the I-beam, the front axle body extends obliquely outward and is provided with a front axle pipe, the I-beam includes horizontal upper web and lower web, the upper web and the lower web are fixedly connected by vertical middle web, so that the upper web, the middle web and the lower web form the I-beam with I-shaped cross section, and the horizontal section of the middle web is wave-shaped.The utility model discloses more reasonable structure design, through reducing the thickness of the upper web of the I-beam, the width of the upper web and the lower web of the I-beam and the thickness of the middle web, the relative circular pipe beam cross section area reduces 29.5%, realizes that the I-beam front axle reduces 12.5% in weight, in addition, the cross section height of the I-beam is higher than that of the circular pipe beam, improves the bending fatigue strength of the front axle, the middle web is designed into wave-shaped, improves the bending deformation stiffness of the front axle, namely, in the whole weight reduction, the bending resistance of the front axle can be improved.

The invention relates to the technical field of flexure performance testing, in particular to a tensile and flexure-resistant performance testing device for an insulated cable. Comprising a base; the controller is mounted on the side surface of the base; the movable seat is connected to the base in a sliding manner; the rotating disc is rotationally connected to the moving seat; the air pump is mounted on the side surface of the movable seat; the fixed plates are symmetrically connected to the side surface of the rotating disc; and the fixed cylinders are symmetrically connected to the fixed plate, the fixed cylinders penetrate through the side face of the rotating disc, and through holes are formed in the fixed cylinders. Through the cooperation of the air pump, the fixed cylinder and the roller, an air diaphragm can be formed between the cable body and the roller, so that the cable can realize non-contact sliding with the roller during a deflection test, specifically, the air pump conveys compressed air to the fixed cylinder through the shunt pipe, and the compressed air is sprayed out through the through hole and the air outlet pipe, so that a dynamic air cushion can be formed; unexpected tensile load and surface abrasion caused by traditional roller friction can be avoided, and it is ensured that the test result only reflects the real bending fatigue performance of the cable.

This invention discloses a method and apparatus for testing the bending fatigue of a steel wire rope in a smart vehicle drum. The apparatus includes a container plate, a steel wire rope clamping assembly mounted on the container plate, and a camera assembly mounted on the opposite side of the container plate. The steel wire rope clamping assembly holds the center point of the steel wire rope to keep it constant. The back plate of the container plate has steel wire rope bending drive assemblies above and below the steel wire rope clamping assembly. These drive assemblies fix the upper and lower ends of the steel wire rope and drive them to swing around the center point. The camera assembly captures an image of the center point of the steel wire rope while the upper and lower ends swing around the center point. The camera assembly is connected to a processing system that tests the bending fatigue of the steel wire rope based on the image changes of its center point. This invention can quickly and accurately identify image changes in the center point of the steel wire rope.

This invention provides a fatigue-resistant high-strength spring steel and its preparation method. By synergistically designing the chemical composition of the iron-based alloy, the low-hydrogen clean molten steel intermediate, the hot rolling controlled cooling, and the quenching-partitioning heat treatment, the steel after stress relief treatment includes tempered martensite and 4-12 vol% retained austenite, and contains nano-precipitates. This results in a fatigue-resistant high-strength spring steel with a tensile strength of 2050-2250 MPa, an elongation after fracture of 8-12%, a reduction of area of ​​30-45%, and a rotational bending fatigue strength of 800-950 MPa. This invention solves the problem of balancing ultra-high strength and long-life fatigue resistance, and the difficulty in achieving both cold-rolling forming processing window and post-stress relief microstructure and dimensional stability. It is suitable for the preparation of high-load spring components.

The invention relates to a gear, a wind generating set and a gear design method, the gear has a main rotation direction, from the cross section view of the gear, a tooth groove of the gear is provided with a working face side, a first tooth profile, a first tooth root transition curve, a second tooth profile and a second tooth root transition curve, the non-working face side is located behind the working face side in the main rotation direction, and the non-working face side is provided with a second tooth profile and a second tooth root transition curve which are connected; wherein the first tooth profile and the second tooth profile are symmetrically arranged relative to a symmetry plane, and a preset distance exists between the connection point of the first tooth root transition curve and the second tooth root transition curve and the symmetry plane. And the connection point of the first tooth root transition curve and the second tooth root transition curve is closer to the second tooth profile than the first tooth profile. According to the technical scheme, the bending fatigue strength of the working face side of the gear can be improved while the size of the gear is not increased.

The invention discloses an anti-bending photovoltaic electrical cable and a preparation method thereof, and belongs to the technical field of electrical cables, and the cable comprises a conductor core, an insulating layer, a flexible middle layer and an outer sheath layer which are sequentially arranged from inside to outside. And the conductor core adopts a heterostructure formed by layering and twisting an inner layer high-ductility metal wire and an outer layer high-tensile strength metal wire in opposite twisting directions. And the flexible middle layer is made of a thermoplastic elastomer with specific hardness. The outer sheath layer is made of a weather-resistant elastomer composite material reinforced by a composite mineral filler, and the composite mineral filler is a mixture of surface-modified flaky talcum powder and chopped glass fibers. The preparation method of the cable comprises the processes of conductor stranding annealing, insulation irradiation crosslinking, co-extrusion of the flexible middle layer and the outer sheath layer and the like. The cable disclosed by the invention is suitable for dynamic bending occasions such as a photovoltaic tracking bracket and the like, and has excellent anti-bending fatigue life and long-term reliability in a severe environment.

This invention discloses a flexible aluminum alloy conductor and its preparation method, relating to the field of metal materials technology. The raw materials of the flexible aluminum alloy conductor include, by weight percentage: A 0.005-2.198 wt%, rare earth elements 0.001-7.670 wt%, Al 90.002-99.999 wt%, and unavoidable impurities with a total content ≤0.105 wt%. The flexible aluminum alloy conductor is prepared by a process of continuous casting, hot rolling followed by rapid cooling, slow cooling with sealing, cold drawing deformation, and segmented temperature-controlled annealing under low-oxygen and nitrogen protection. Through the synergistic effect of Fe and rare earth elements, combined with strict control of Si content, the flexible aluminum alloy conductor achieves good flexibility and resistance to bending fatigue while maintaining high conductivity and strength.

The utility model discloses a quick sample replacement fixture of a cantilever beam rotating bending fatigue testing machine, which comprises a mounting seat, a moving mechanism mounted on the mounting seat, clamping seats arranged at two ends of the moving mechanism, clamping mechanisms rotationally mounted on opposite side surfaces of the clamping seats, and driving mechanisms arranged on the clamping mechanisms. According to the device, through the synergistic effect of the moving mechanism and the driving mechanism, rapid clamping and dismounting of the samples are achieved, the moving mechanism can make the clamping base rapidly move to a proper position so as to adapt to the samples of different lengths, and the driving mechanism can rapidly drive the clamping mechanism to complete clamping and loosening actions on the samples of different shapes and specifications; the time for replacing the sample is greatly shortened, and the test efficiency is improved.

The invention discloses a mining machinery multi-core cable convenient to bend and lay, which comprises a plurality of wire core groups and an outer sheath arranged outside the plurality of wire core groups, each wire core group comprises a power wire core, a control wire core and a signal wire core, and each wire core group comprises a conductor and an insulating layer wrapping the conductor; the cable also comprises an elastic buffer unit array structure, and the elastic buffer unit array structure is arranged between the wire core group and the outer sheath. According to the invention, the bending stress is effectively absorbed and dispersed through the elastic buffer unit array structure, the bending rigidity of the cable is remarkably reduced, and the bending fatigue resistance of the cable is greatly improved; signal interference is avoided through an asymmetric clover-shaped electromagnetic isolation and counterweight structure, and the cable balance is optimized; through an anchoring structure of the tensile woven mesh and the sheath, relative displacement between the outer sheath and the internal elastic buffer unit array structure is prevented.

The invention relates to the technical field of ocean engineering special cables, and discloses a high-tensile trailing cable for ocean engineering and a preparation method of the high-tensile trailing cable. The cable sequentially comprises a cable core, an inner sheath, a gradient composite tensile layer, a segmented functional sheath and an outer sheath from inside to outside, wherein the gradient composite tensile layer is tightly coated outside the inner sheath and comprises an inner layer and an outer layer, the inner layer is a high-modulus fiber braid layer, and the outer layer is a metal and fiber composite braid layer; the gradient composite tensile layer is coated with the segmented functional protection layer, the segmented functional protection layer is divided into two sections with different structures in the length direction of the cable, the two sections are a top section used close to the water surface and a bottom section used for a deep water area, the top section adopts a corrugated composite protection layer structure, and the bottom section adopts a smooth bonding protection layer structure. The cable provided by the invention realizes unification of high tensile strength, excellent dynamic bending fatigue performance and high hydrostatic pressure crushing resistance, and solves the problem that a cable with a single structure cannot adapt to full-sea-depth working conditions.

This invention discloses a bending fatigue enhancement structure for flat cables, relating to the field of flat cable technology. It includes a wear-resistant outer sheath, a flexible skeleton, an elastic inner liner, and a composite conductor bundle. The wear-resistant outer sheath covers the flexible skeleton, with bending stress cores at the outer ends. The flexible skeleton is internally covered by an elastic inner liner, which contains two spaced-apart composite conductor bundles. The flexible skeleton has grooves filled with an anti-oxidation coating layer, within which the bending stress cores are fixed. The interior features stress-dispersing adhesive grooves intersecting with the grooves, and high-toughness reinforcing ribs with abrasion-resistant protective sleeves are installed at the four corners. The elastic inner liner has a water-blocking tape wrapping layer on its outer side and a flame-retardant isolation layer inside. The composite conductor bundles are wrapped with cable core fixing rings and an electromagnetic shielding layer. This structure, through multiple stress dispersion, protection, and positioning designs, significantly improves the cable's bending fatigue resistance, ensuring stable transmission and safe operation, and is suitable for high-frequency bending scenarios.

The application discloses a kind of cathode metal plate bending fatigue test device, it relates to cathode metal plate test technical field.The cathode metal plate bending fatigue test device includes fixed component and test component.Fixed component includes rack and two support frames.Rack is fixedly arranged, two support frames are symmetrically fixed on rack along transverse direction, and cathode metal plate is fixed between two support frames.Test component includes two cylinder fixed beams, two stroke cylinders and two nylon blocks.Two cylinder fixed beams are fixed on rack along longitudinal direction, and are arranged at the two sides of cathode metal plate, two stroke cylinders are respectively fixed on two cylinder fixed beams, and the output end of two stroke cylinders faces cathode metal plate, two nylon blocks are respectively fixed on the output end of two stroke cylinders.The output end of two stroke cylinders can alternately extend or retract, so that two nylon blocks carry out periodic ejection action to the two sides of cathode metal plate.

The invention provides a nickel-titanium alloy wire with the ultra-high fatigue life and a preparation method and application thereof.The preparation method of the nickel-titanium alloy wire with the ultra-high fatigue life comprises the following steps that raw materials of titanium, nickel, tantalum, zirconium, hafnium and cobalt are taken to be smelted, a cast ingot is prepared, then forging is conducted, and a blank is obtained; the blank is subjected to multi-pass cold drawing, once intermediate annealing is carried out when the accumulated true strain value of the wire obtained through cold drawing reaches the range of 0.18-0.32, and the steps are repeated till the obtained wire reaches the target size; and the wire is subjected to heat treatment, and the nickel-titanium alloy wire with the ultra-high fatigue life is obtained. According to the preparation method of the nickel-titanium alloy wire with the ultra-high fatigue life, the prepared nickel-titanium alloy wire has extremely high flexibility, ultra-long rotating bending fatigue life and excellent phase change temperature consistency.

The application discloses a kind of simulation under complex load aircraft conduit connector bending fatigue testing device, it is related to fatigue strength detection technical field, its technical scheme includes: including servo motor, coaxality adjusting system, deflection adjusting system, sealing round bar, test piece, pressure sensor, displacement sensor, fixed platform and complex load loading mechanism, complex load loading machine can accurately simulate circumferential load in actual working condition, complex load is applied in the same test process, real restoration complex stress state of conduit connector in aircraft hydraulic system, make test result more close to actual use situation, greatly improve the reliability of test data, simultaneously, by pressure sensor, displacement sensor and position sensor, test result is monitored in real time, avoid abnormal test data or equipment damage due to limit failure, simultaneously set locking device, prevent handle accidental movement during test process and lead to limit failure.

This utility model discloses a bending moment locking device and a pure bending fatigue tester for a pure bending fatigue specimen, relating to the field of mechanical testing technology. It includes: multiple limiting rods, a first positioning baffle, a second positioning baffle, and multiple first limiting blocks, with each limiting rod arranged in parallel. The first positioning baffle is connected to one end of a limiting rod and can be positioned along the length of the limiting rod. The second positioning baffle is arranged parallel to the first positioning baffle and is slidably connected to the limiting rod, maintaining its slidable position. The first limiting block is fixedly connected to the end of the limiting member away from the first positioning baffle and is located on the side of the second limiting baffle away from the first limiting baffle. The distance between the two opposite sides of the first and second positioning baffles when the second positioning baffle and the first limiting block are pressed together is the standard lever arm length. The structure is simple, easy to use, and effectively ensures the accuracy of the test data.

The invention belongs to the technical field of metallurgy, and particularly relates to hot forming steel special for a commercial vehicle rim and a production method thereof. The steel comprises the following chemical components in percentage by mass: 0.18%-0.2% of C, 1.1%-1.3% of Mn, 0.1%-0.15% of Si, less than or equal to 0.003% of S, less than or equal to 0.013% of P, 0.15%-0.17% of Cr, 0.03%-0.04% of Alt, less than or equal to 0.004% of N, 0.045%-0.055% of Ti, 0.028%-0.032% of Nb, 0.0025%-0.0035% of B and the balance of Fe and inevitable impurities, and the content of Ti and the content of N meet the condition that Ti / N is greater than or equal to 16. The invention further provides a production method based on the full endless continuous casting and rolling production line, through accurate component design and process control, the welding performance and the bending fatigue performance of the material are remarkably improved while the 1300MPa-grade strength is guaranteed, the cover annealing procedure is completely omitted, and short-process and low-cost stable production of the high-performance rim steel is achieved.

This invention belongs to the field of road assembly technology and discloses a method, device, equipment, and storage medium for evaluating the integrity of concrete pavement. The method includes: obtaining a bending fatigue remaining life factor based on stiffness information; obtaining a bidirectional load transfer capacity factor for the assembled surface based on the difference in longitudinal and transverse loading displacements and the weights of the longitudinal and transverse load transfer coefficients; obtaining a structural interlayer vertical deformation coordination factor based on the assembled surface displacement, support layer displacement, and displacement tolerance; and obtaining a dynamic integrity index based on multiple factors for integrity evaluation. This invention quantifies pavement performance from three key dimensions—fatigue life, load transfer, and interlayer deformation—by calculating the bending fatigue remaining life factor, the bidirectional load transfer capacity factor for the assembled surface, and the structural interlayer vertical deformation coordination factor. It not only reflects the instantaneous state but also adjusts with changes in load and environment, enabling real-time evaluation during construction acceptance and long-term monitoring, thus improving the timeliness and accuracy of the evaluation.

This invention belongs to the field of automotive parts manufacturing, specifically involving a simulation system, method, equipment, and medium for evaluating the impact of materials on wheels. Based on a target wheel test bench, a corresponding simulation model is established; several sets of material properties, yield strength and tensile strength, are input to generate SN curves; corresponding stress criteria are generated based on the SN curves; the corresponding weight is obtained, optimization results are obtained, and the optimization results are evaluated. This invention converts the wheel bending fatigue life into equivalent fatigue strength through SN curves, and uses high-order mesh deformation technology to quickly and efficiently evaluate the impact of yield strength and tensile strength on wheel weight. It provides a scientific and accurate simulation prediction method for evaluating the impact of material properties on wheel weight, with broad application prospects and market value. This addresses the problem of difficulty in quickly and accurately evaluating the quantitative impact of new materials on wheel weight under bending fatigue conditions.

The invention discloses a variable-diameter and variable-wall-thickness drill rod for large-diameter directional drilling of a top plate of an extra-thick coal seam. The drill rod is divided into four functional sections in the axial direction, namely, a near-bit strengthening section, a deflection / stable deflection flexible section, a main body transmission section and a tail connection strengthening section. Different outer diameters and wall thicknesses are adopted for all the functional sections according to the actual stress state of the functional sections in the directional drilling process, and matching of material distribution and stress requirements is achieved. The near-bit strengthening section adopts the maximum outer diameter and the thickest wall thickness so as to bear high torque and abrasion; the deflection / stable deflection flexible section has certain flexibility on the premise of ensuring the bending fatigue strength; the wall thickness of the main body transmission section is optimized to realize light weight; and the tail connection reinforcing section improves the connection reliability through local thickening. The problems that a traditional equal-diameter equal-wall-thickness drill rod is integrally heavy, locally prone to damage, insufficient in adaptability and the like in large-diameter directional long drilling construction are solved, the overall service life of the drill rod is prolonged, and the drilling efficiency and economic benefits of the drill rod are improved.

1. The name of the design product: endoscope bending tester. 2. The use of the design product: for endoscope bending fatigue strength and durability detection. 3. The design points of the design product: in shape. 4. The picture or photo that best indicates the design points: perspective view.

The invention discloses a drill bit double-layer surfacing method based on interlayer temperature control, and belongs to the technical field of surfacing processes. The double-layer surfacing technology is adopted, layer-by-layer surfacing of a base material, a transition layer and a working layer is achieved by controlling the interlayer temperature of double-layer surfacing, and the problems that in actual use of a drill bit, cracks and peeling are prone to occurring, bending fatigue resistance and interface bonding strength are seriously insufficient, and reliability is poor are solved.

Provided are: a rubber composition for sidewalls, which is capable of producing sidewalls having excellent bending fatigue resistance and capable of improving low fuel consumption performance; and a sidewall obtained by using the rubber composition for at least a part of the sidewalls. This rubber composition for sidewalls contains 0.1-30 parts by mass of a modified liquid diene rubber (B) having a functional group derived from a silane compound satisfying specific conditions and 5-80 parts by mass of a filler (C) containing a specific silica (C1) per 100 parts by mass of a solid rubber (A) containing a natural rubber and / or an isoprene rubber (A1) and a butadiene rubber (A2).

The utility model discloses a bending fatigue resistant data transmission cable, which comprises a signal pair, two power lines and a plurality of conductors, the signal pair comprises two signal lines, the plurality of conductors axially penetrate through the signal lines and the power lines, and the two power lines and the signal pair are arranged side by side; comprising an outer coating layer, water-blocking yarn and a water-blocking tape, the water-blocking yarn is located between the water-blocking tape and the outer coating layer, and the outer coating layer wraps the signal pairs and the two power lines; according to the utility model, the water-blocking yarns and the water-blocking tape are added to reduce the corrosion of water to the cable, and the waterproof performance of the cable is improved.

The present application relates to the field of rubber production, in particular to a special rubber V belt for raising machine and a production process thereof. The present application increases the contact surface of the belt and the pulley, improves the stress area of the V belt, and improves the wear resistance of the V belt by optimizing the V belt angle; the position of the skeleton wire is optimized, the neutral layer position of the V belt is adjusted, the bending deformation amplitude of the compression layer is reduced, and the bending fatigue life of the V belt is improved; and the silicon carbide heat conductor is a material with high thermal conductivity, the thermal conductivity of natural rubber is 0.15-0.21 W / (m.K), which is a poor conductor of heat, and the running temperature of the belt is reduced by 10 DEG C after adding the silicon carbide heat conductor, and the service life is improved by 40%.

The utility model discloses an anti-breaking electronic connecting line, and relates to the technical field of electronic connecting lines. Comprising a wire body and a connecting terminal head, spiral portions are arranged at two ends of the wire body, the wire body is connected with the connecting terminal head through the spiral portions, the wire body comprises a wire core, a PP filling rope, a glass tape wrapping layer, a TPU inner sheath, an aluminum foil shielding tape and a TPU outer sheath, and the glass tape wrapping layer wraps the outer side of the wire core. According to the anti-breaking electronic connecting line, the arranged spiral part has telescopic and bending capabilities and has good flexibility and bending resistance when needed, so that the joint of the electronic connecting line has a firmer design and can bear more plugging and bending, and meanwhile, the TPU sheaths arranged on the inner layer and the outer layer have good bending fatigue resistance, so that the anti-breaking electronic connecting line has good anti-breaking performance. And the connecting wire can withstand frequent bending and twisting and is not easy to damage, so that the connecting wire is more durable in occasions needing frequent bending or twisting.