Torsional Friction Research Articles

Experimental Study on Torsional Friction of Stringing Blocks on Conductor in Tension Stringing Construction

An experimental study was conducted to analyze the torsional friction effect of stringing blocks on the conductor during tension stringing construction. By analyzing the torsional friction force of stringing blocks on the conductor, the torsional friction experimental device of the stringing blocks on the conductor was designed. The torsional friction torque of the JL/G1A-630/45-45/7 Aluminum Conductor Steel Reinforced (ACSR) under the different tensions and wrap angles passing through the stringing blocks was measured, and then the friction coefficient was obtained. The experimental results show that the torsional friction coefficient of the stringing blocks to the conductor μ decreases with the increase of the tension of the conductor and the wrap angle passing through the stringing blocks. The relationship between the coefficient of friction and the wrap angle and tension of the conductor passing through the stringing blocks is obtained by fitting, and the formula for calculating the torsional frictional torque is obtained.

Design and testing of a DNA-like torsional structure for energy absorption

A torsional structure with a DNA-like chiral core is proposed and investigated for energy absorption with a frictional mechanism. The DNA-like chiral core can generate a twisting deformation under axial loading. Based on this behavior, the proposed torsional structure exhibits a unique energy absorption capacity by structural collapse and torsion-induced friction. Additive manufacturing is used to prepare five sets of metal specimens with the new DNA-like chiral core structure. A series of quasi-static compression experiments are carried out to obtain the compressive stress–strain relationship and induced twisting angle of our designed structure. The experimental results show distinct energy absorption mechanism and effectiveness of the design which are subsequently used to validate the finite element simulation. The results of the experiment and numerical analysis show that the torsional friction between the top cap of the structure and the outer block can absorb around 10% of the total compression energy input. Furthermore, geometry parametric studies are conducted to investigate the effects of design parameters on energy absorption property of the proposed structure.

A transfer learning-based digital twin for detecting localised torsional friction in deviated wells

Digital twins seek to replicate a physical structure in a digital domain. For a digital twin to have close correspondence to its physical twin, data are required. However, it is not always possible, or cost-effective, to collect a complete set of data for a structure in all configurations of interest. It is nonetheless useful to repurpose data to help validate predictions for different configurations and scenarios. This statement is true in drilling applications, where, for example, the length of the drill string is altered throughout operation. This paper demonstrates how transfer learning, in the form of three domain-adaptation methods, — transfer component analysis (TCA), maximum independence domain adaptation (MIDA) and geodesic flow kernel (GFK) — can be used to construct a digital twin for localising torsional friction in deviated wells under structural changes (e.g., when the drill column gets longer). The method uses a physics-based torsional model to train a machine-learning classifier that can localise torsional friction for a given drill string length and diameter, where friction localisation labels are known (source). As the length or diameter of the drill string are altered in the field, transfer learning is utilised to map the classifier from the labelled (source) scenario onto these unlabelled (target) scenarios. As a result, transfer learning improves the performance of the classifier when applied to the target data, and increases the domain of validity for the classifier. The performance of the classifier, and therefore its suitability to new drill-string configurations, is estimated by utilising two different distance metrics between the source and a proposed target dataset.

Design of Insertion Mechanism with Friction Wheels for Cannula Flexible Needle Based on TRIZ

Background: Flexible needle insertion is one of the minimally invasive surgeries, which takes advantage of the lateral force acted on the bevel tip to make the needle shaft bend when inserted into the tissue. The bending makes the needle avoid the obstacles (like bones, veins, nerves, etc.) in order to reach the target. However, the traditional flexible needle neither can change its curvature of the path, nor can realize a precise control because of the torsional friction between the needle and the tissue. Hence, a cannula flexible needle was proposed to overcome the drawbacks, which consists of a cannula and a stylet. Also, there is a need of an insertion mechanism for the cannula flexible needle in robot-assisted surgery. Objective: The aim of this paper is to innovatively design an insertion mechanism with friction wheels for the cannula flexible needle, which is used as an end-effector in robot-assisted surgery system. The mechanism is supposed to realize the coordinated driving of the cannula and the stylet in order to achieve variable curvatures of paths. Methods: Making references of the patents and research papers on needle insertion mechanisms, and based on the requirement of degree of freedom for the cannula flexible needle insertion, the insertion mechanism for the cannula flexible needle is designed by using the TRIZ theory. The conflicts matrix analysis, the invention principles and the substance-field analysis are used to innovatively design the driving scheme and the synchronous motion mechanism. Results and Conclusion: In this paper, the concrete structure design of the insertion mechanism for the cannula flexible needle is achieved, which is compact and simple. The friction coefficient between the needle and the wheels, and the pretightening force between both wheels are calculated through the data from experiments. The insertion accuracy of friction wheel mechanism is tested and analyzed through experimentation. The results show that the maximum placement error of the needle executed by the insertion mechanism is less than 0.5 mm, which meets the demands of surgical operations.

A modified piezoelectric ultrasonic composite oscillator technique for simultaneous measurement of elastic moduli and internal frictions at varied temperature.

In this work, a modified piezoelectric ultrasonic composite oscillator technique (M-PUCOT) is developed for measuring a material's elastic moduli and internal frictions, as a function of temperature. Different from the traditional PUCOT that employs two quartz bars as the drive and gauge, here, a single small piezoelectric transducer (PZT) ring is used to drive and sense longitudinal or torsional vibration in a cylinder specimen. Because of the strong piezoelectric effect and relatively large bandwidth of the PZTs compared to their quartz counterpart, the frequency match condition between the transducer and the specimen is not required in this M-PUCOT. For high temperature measurement, a fused quartz spacer, whose resonance frequency matches the specimen's, is bonded between the transducer and the specimen to provide thermal insulation. First, the united equivalent circuit of the transducer- (spacer) -specimen composite system was derived. Then, Young's modulus, longitudinal friction, shear modulus, and torsional friction were explicitly obtained by measuring the resonance frequency and antiresonance frequency of the 2- or 3-component system's electrical susceptance curve using an impedance analyzer. The accuracy of this method was validated both by measuring the system's amplitude-frequency curves using a laser vibrometer and through finite element simulations. The repeatability error of the M-PUCOT is only ∼0.2% for moduli measurement and ∼2.5% for internal friction measurement, which is very promising for studying the moduli and internal friction variations during damage, fatigue, and phase transitions. Finally, the M-PUCOT was employed to measure the variations in moduli and internal frictions of an Fe64Ni36 Invar alloy from room temperature to 500 °C. Results show that above the ferromagnetic phase transition temperature Tc, both moduli reach their maxima, and both internal frictions reach their minima. The proposed M-PUCOT is expected to be widely used in the near future for its quick measurement, high repeatability, and low cost.

A Synthetic Bottle-brush Polyelectrolyte Reduces Friction and Wear of Intact and Previously Worn Cartilage.

A poly(7-oxanorbornene-2-carboxylate) polymer containing pendent triethyleneglycol (TEG) chains of 2.8 MDa ("2.8M TEG") was synthesized and evaluated for long-term lubrication and wear reduction of ex vivo bovine cartilage as well as for synovitis in rats and dogs after intra-articular administration. Bovine cartilage surfaces were tested under torsional friction for 10,080 rotations while immersed in either saline, bovine synovial fluid (BSF), or 2.8M TEG. For each solution, coefficient of friction (μ), changes in surface roughness, and lost cartilage glycosaminoglycan were compared. To directly compare 2.8M TEG and BSF, additional samples were tested sequentially in BSF, BSF, 2.8M TEG, and then BSF. Finally, another set of samples were tested twice in saline to induce surface roughness and then tested in BSF, Synvisc, or 2.8M TEG to determine each treatment's effect on worn cartilage. Next, male Lewis rats were injected in one knee with 2.8M TEG or saline and evaluated for effects on gait, and female beagles were injected with either 2.8M TEG or saline in one knee, and their synovial tissues analyzed for inflammation by H&E staining. Treatment with 2.8M TEG lowers μ, lessens surface roughness, and minimizes glycosaminoglycan loss compared to saline. The 2.8M TEG also reduces μ compared to BSF in pairwise testing and on worn cartilage surfaces. Injection of 2.8M TEG in rat or beagle knees gives comparable effects to treatment with saline, and does not cause significant synovitis.

Improved Methods Aid Understanding and Mitigation of Stick/Slip Torsional Vibrations

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 189673, “Improved Methods To Understand and Mitigate Stick/Slip Torsional Vibrations,” by J.R. Bailey, SPE, G.S. Payette, SPE, and L. Wang, SPE, ExxonMobil, prepared for the 2018 IADC/SPE Drilling Technology Conference and Exhibition, Fort Worth, Texas, USA, 6–8 March. The paper has not been peer reviewed. Historically, prediction of stick/slip vibrations in advance of drilling has been fraught with challenges. Although the factors influencing stick/slip, and the directional changes required to mitigate it, are known, a need exists for a simple method to determine quantitatively the degree of dysfunction and the effects of redesign parameters. This paper will show how stick/slip vibration distributions can be used to guide drillstring and parameter redesign to mitigate stick/slip in the next well. Background Torsional vibrations, also known as stick/slip, occur as the rotational speed of the bit and drillstring vary because of stiffness, inertia, and torsional friction interactions. In some wells, these torsional/rotational fluctuations are not severe and may not reach full stick/slip, which occurs when the bit comes to a full stop in the torsional vibration cycle. The drilling data obtained in the drilling of a well are displayed typically as time or depth tracks, with different parameters shown on the same or adjacent tracks over the corresponding time or depth interval. Although of interest, this display of data is limited. It does not provide a direct indication of the amount of dysfunction present over the duration of the interval. A histogram is a particularly useful display of the distribution of data values. In the case of stick/slip vibrations, the torsional-severity estimate (TSE) is a measure of proximity to full stick/slip. A TSE value of 0.0 represents no torsional vibrations, where the entire drillstring is turning at a constant angular velocity. A TSE of 1.0 represents full stick/slip, in which the rotary speed at the surface is constant but the bit speed varies sinusoidally between zero and twice the surface rotary speed. Values of TSE greater than 1.0 indicate time intervals in which the bit comes to a complete stop and then accelerates to more than twice the surface rotational speed. The most severe cases may even involve negative rotation of the bit. Analytical tools that help assess the degree of torsional vibrations can be useful, especially in those instances where known remediation techniques are not available or may be costly. A variety of methods exists to address torsional vibration problems, and the most-cost-effective method may be the method of choice. The authors are not aware of simple analytical methods that can provide quantitative evaluation to address the following: How will the stick/slip problem change if the drillstring design is modified? How will stick/slip change if the operating parameters are modified? The bit-design parameters may be varied to increase or decrease bit torque. How will changes to the bit friction factor affect stick/slip vibrations in a certain application?

Numerical investigation of the vortex-induced vibration of an elliptic cylinder free-to-rotate about its center

Vortex-induced vibration (VIV) of an elliptic cylinder free to rotate about its center is numerical studied at Reynolds number 2580≤Re≤15490. The vibration and rotation responses occurring simultaneously are considered with normalized torsional friction varied from 3.34×10−4 to 1.17. A two-way fluid–structure interaction (FSI) approach is used to solve the incompressible flow equations and the structure motion including the vibration and rotation in two dimensions. The numerical results indicate that the torsional friction is a key factor, determining the rotation response and then affecting the vibration amplitude. When the torsional friction is too large or the reduced velocity is too small, the elliptic cylinder is unable to rotate, while too small friction leads to transverse galloping instead of the desynchronized region. For the elliptic cylinder with moderate frictions, the response occurs similar as the circular cylinder, but the amplitude in the desynchronized region is larger than the circular cylinder due to the hydrodynamic instability. The results show four kinds of rotation response, which are associated with the time-averaged torque and the flow field around the elliptic cylinder. Compared to the non-rotatable elliptic cylinder with 0° attack angle, the rotatable cylinder vibrates more vigorously.

Torsional Friction Behavior of Contact Interface Between PEEK and CoCrMo in Calf Serum

Polyether ether ketone (PEEK) and its composites are recognized as alternative bearing materials for use in arthroplasty because of their excellent mechanical properties. In this paper, torsional friction tests of PEEK against the CoCrMo alloy, simulating the contact mode between the prosthesis tibia and femur, were carried out under a 25% calf serum solution in a Leeds Prosim knee simulator. The torsional friction behavior of PEEK against the CoCrMo alloy was investigated under various normal loads (1000 N, 1600 N and 2200 N), torsional angular displacement amplitudes (±1 deg, ±3 deg, and ±5 deg), and the number of cycles (7500, 15,000, and 30,000). The torsional friction characteristics and damage mechanism are discussed. The results show that PEEK exhibited low friction coefficient under the different conditions. With increases in the torsional angle and normal load, three types of torque/angular displacement amplitude (T–θ) curves (i.e., linear, parallelogram, and elliptical loops) were observed and analyzed during the process of torsional friction. With the increase of the torsional angle, the coefficient of friction decreases. And the contact states change from the partial slip regime to the slip regime. The greater the torsional angle displacement, the more severe the damage to the PEEK surface. With an increase in the normal load, the wear scars increased. The wear depth is deepened and the width is widened, and the wear gradually becomes serious with an increase in the load. The small load is more likely to cause damage to the central area of PEEK, and the larger load causes more serious damage to the marginal region. The central and marginal regions of the PEEK sample have different wear characteristics. The worn surfaces of the central regions were characterized by convex ridges resulting from plastic deformation, while curved ploughs and fatigue peeling appeared in the marginal region. The wear mechanism of PEEK in the central region is plastic deformation, while fatigue wear and abrasive wear mainly appeared in the marginal region.

Torsional friction behavior of the contact interface between the materials of an artificial knee joint replacement

The torsional friction behavior of the materials (CoCrMo alloy and ultra-high-molecular-weight polyethylene (UHMWPE)) that are used in artificial knee joint replacement (AKJR) were investigated under dynamic loading. The torsional friction torque, wear loss and scars and stress distribution were analyzed and compared. The results show the following: (1) the friction torque declines rapidly at the beginning of the experiments, and meanwhile, the maximum normal load and the torsional angle amplitude show very little effect on the steady value; (2) the wear loss decreases with the increased torsional angle amplitude but increases with the increased maximum normal load; additionally, as the cycle times increase, the wear rate decreases, and the wear is minimal; (3) unloading and secondary loading significantly reduce the friction and wear of the materials, and thus, patients should rest after prolonged exercise to reduce wear; (4) the margins of UHMWPE and CoCrMo are worn, and the wear mechanism is abrasive wear; (5) around the center of the UHMWPE, the surface is peeled off, and the wear mechanism is fatigue wear; and (6) in terms of the compressive stress and shear stress, the calculated results from a finite element model match the experimental results well.

CFD analysis of energy harvesting from flow induced vibration of a circular cylinder with an attached free-to-rotate pentagram impeller

A new converter consisting of an elastically mounted circular cylinder and a free-to-rate pentagram impeller is proposed to harness hydrokinetic energy from water currents. The vibration energy of the cylinder and the rotation energy of the impeller are harvested simultaneously. The two-way fluid-structure interaction simulations are employed to investigate the vibration and rotation response of the converter. The simulated Reynolds number range is 14,000 < Re < 80,000, falling in the TrSL2 (transition of shear layer 2) and TrSL3 regimes. The results indicate that the vibration amplitude of the converter increases with increasing of the flow velocity, and the growth becomes faster at high reduced velocity (Ur). The presence and rotation of the impeller contribute to the hydrodynamic instability of the system at Ur ≥ 9, where the rotational direction is constantly changing. The hydrodynamic instability brings about a wider flow wake and unstable vortex shedding, resulting in the enhancement of vibration and the increase of power. For such a rotation symmetric structure, increasing the torsional friction does not play a significant role in suppressing the hydrodynamic instability. The estimated power generating capacity is sensitive to flow velocity and additional damping ratio. The average power efficiency is about 22.6%, and the power density for a 5D × 5D staggered configuration with ζharn of 0.031374 can reach 885.53 W/m3.

Reinforcement of articular cartilage with a tissue-interpenetrating polymer network reduces friction and modulates interstitial fluid load support.

Osteoarthritis (OA) is associated with increased articular cartilage hydraulic permeability and decreased maintenance of high interstitial fluid load support (IFLS) during articulation, resulting in increased friction on the cartilage solid matrix. This study assesses frictional response following in situ synthesis of an interpenetrating polymer network (IPN) designed to mimic glycosaminoglycans (GAGs) depleted during OA. Cylindrical osteochondral explants containing various interpenetrating polymer concentrations were subjected to a torsional friction test under unconfined creep compression. Time-varying coefficient of friction, compressive engineering strain, and normalized strain values (ε/εeq) were calculated and analyzed. The polymer network reduced friction coefficient over the duration of the friction test, with statistically significantly reduced friction coefficients (95% confidence interval 14-34% reduced) at equilibrium compressive strain upon completion of the test (P=0.015). A positive trend was observed relating polymer network concentration with magnitude of friction reduction compared to non-treated tissue. The cartilage-interpenetrating polymer treatment improves lubrication by augmenting the biphasic tissue's interstitial fluid phase, and additionally improves the friction dissipation of the tissue's solid matrix. This technique demonstrates potential as a therapy to augment tribological function of articular cartilage.

A Statistical Model for Torsional Friction of Plate-on-Plate Contact

A statistical model for torsional friction of plate-on-plate contact is constructed. The torsional responses including T–θ curves, proportion of slip asperities, and the radius of gross slip can be obtained from the model. The torsional friction response of monomer cast (MC) nylon against 316L stainless steel was calculated with this model and a torsional friction experiment of MC nylon against 316L stainless steel was performed to verify the model. The calculated T–θ curves exhibit different shapes under different torsional angular displacements. The calculations demonstrated that the torsional regime determined only through T–θ curves was inaccurate. The statistical results of asperities located at the torsional interface more directly reflected the torsional regime. The T–θ curves obtained from theoretical calculation and experiments are consistent in shapes, whereas the torque magnitude from the theoretical calculation is larger than that from experiments. When gross slip is indicated by the maximum torque on the T–θ curves, about 93% of the contact asperities were in a slip status rather than 100% and the gross slip radius in the whole torsional contact interface was about 3 mm.

Research on torsional friction behavior and fluid load support of PVA/HA composite hydrogel

Hydrogels have been extensively studied for use as synthetic articular cartilage. This study aimed to investigate (1) the torsional friction contact state and the transformation mechanism of PVA/HA composite hydrogel against CoCrMo femoral head and (2) effects of load and torsional angle on torsional friction behavior. The finite element method was used to study fluid load support of PVA/HA composite hydrogel. Results show fluid loss increases gradually of PVA/HA composite hydrogel with torsional friction time, leading to fluid load support decreases. The contact state changes from full slip state to stick–slip mixed state. As the load increases, friction coefficient and adhesion zone increase gradually. As the torsional angle increases, friction coefficient and slip trend of the contact interface increase, resulting in the increase of the slip zone and the reduction of the adhesion zone. Fluid loss increases of PVA/HA composite hydrogel as the load and the torsional angle increase, which causes the decrease of fluid load support and the increase of friction coefficient.

Influence of porosity on collisions between dust aggregates

Context. Collisions between dust particles may lead to agglomerate growth or fragmentation, depending on the porosity of the dust and the collision velocity.Aims. We study the effect of agglomerate porosity and collision velocity on aggregate fragmentation and agglomeration.Methods. Granular-mechanics simulations are used to study the outcome of head-on dust aggregate collisions. The aggregates are composed of silica grains of 0.76 μ m radius and have filling factors of between 0.08 and 0.21. The simulations incorporate repulsive and viscoelastic, dissipative normal forces, and intergrain adhesion. The tangential forces are composed of gliding, rolling, and torsional friction. To study the effect of aggregate porosity, we prepared spherical aggregates with identical radius but differing particle numbers. Results. The threshold velocity for agglomerate fragmentation decreases with the porosity of the aggregates. Porous aggregates tend to fragment more easily, and the fragments are irregularly shaped. In the agglomeration regime, the merged aggregate is more compact than the initial collision partners. The collision velocity at which compaction is highest is independent of the initial porosity.

Torsional Tribological Behavior and Torsional Friction Model of Polytetrafluoroethylene against 1045 Steel.

In this work, the plane-on-plane torsional fretting tribological behavior of polytetrafluoroethylene (PTFE) was studied. A model of a rigid, flat-ended punch acting on an elastic half-space was built according to the experimental conditions. The results indicate that the shape of T–θ curves was influenced by both the torsional angle and the normal load. The torsion friction torque and wear rate of PTFE exponentially decreased when the torsion angle rose. The torsional torque increased from 0.025 N·m under a normal load of 43 N to 0.082 N·m under a normal load of 123 N. With sequentially increasing normal load, the value of torque was maintained. With rising normal load, the wear mass loss of PTFE disks was increased and the wear rate was decreased. Good agreement was found with the calculated torque according to the model and the experimental torque except for that under a normal load of 163 N. The difference under a normal load of 163 N was caused by the coefficient of friction. Usually the coefficient of friction of a polymer decreases with increasing normal load, whereas a constant coefficient of friction was applied in the model.

Effect of Temperature on Mechanical Properties and Torsional Friction Behaviors of Bogie Center Plate

In order to simulating the torsional friction of the center plate during the railcar body traveling on different railway curves at different environmental temperatures, the torsional friction behavior of monomer casting (MC) nylon composites which was used to make center plate, at temperatures of −25 °C to 50 °C was studied. With increasing temperature, the mechanical properties of nylon composites were weakened, whereas the visco-elastic property was boosted. Under torsional angle of 1.8 deg and 0.96 deg, all the torque–angular displacement (T–θ) curves exhibited the quasi-parallelogramic shape at various temperatures. When the temperature was higher than 25 °C under 0.42 deg, the shape transformed from elliptic to parallelogrammic. This indicated that the torsional regime changed from a partial slip to a gross slip. With increasing temperature, the torsional torque decreased and the wear mass loss increased because of weakened mechanical properties. The wear mechanism changed from slight plastic flow at low temperature to serious adhesive and three-body abrasion wear at high temperature.

Aggregate Constraints for Virtual Manipulation with Soft Fingers.

Interactive dexterous manipulation of virtual objects remains a complex challenge that requires both appropriate hand models and accurate physically-based simulation of interactions. In this paper, we propose an approach based on novel aggregate constraints for simulating dexterous grasping using soft fingers. Our approach aims at improving the computation of contact mechanics when many contact points are involved, by aggregating the multiple contact constraints into a minimal set of constraints. We also introduce a method for non-uniform pressure distribution over the contact surface, to adapt the response when touching sharp edges. We use the Coulomb-Contensou friction model to efficiently simulate tangential and torsional friction. We show through different use cases that our aggregate constraint formulation is well-suited for simulating interactively dexterous manipulation of virtual objects through soft fingers, and efficiently reduces the computation time of constraint solving.

Torsional tribological behavior of polytetrafluoroethylene composites filled with hexagonal boron nitride and phenyl p-hydroxybenzoate under different angular displacements

Purpose – The purpose of this paper is to investigate the effect of hexagonal boron nitride (h-BN) and poly (phenyl p-hydroxybenzoate) (PHBA) on improving the torsional tribological behavior of polytetrafluoroethylene (PTFE). Design/methodology/approach – This paper investigates the torsional tribological behavior of PTFE composites filled with h-BN and PHBA under different angular displacements with a plane-on-plane torsional friction tester. The worn surface of PTFE composites was investigated by using a scanning electron microscope. Findings – The shape of T–Θ curves of PTFE composites was influenced by both content fillers and torsional angule. The material with a higher coefficient of sliding friction exhibited the larger torsional angle under which the torsional regime transited from a partial slip to a gross slip. PTFE composites filled with 20 weight per cent PHBA and 10 weight per cent h-BN showed the best anti-wear properties. The specific wear rate of composites exhibits a negative correlation with material hardness. The wear volume loss presents a positive correlation with friction dissipation energy. The specific wear rate of all composites decreased with increasing torsional angle. The dominant wear mechanism of pure PTFE was adhesive wear. The slight plastic flow and plowing occurred on the worn surfaces of PTFE composites because of the higher hardness of composites and the lubrication of h-BN particles with layer crystal structure. Originality/value – This paper put forward a kind of PTFE composite with low torsional wear rate, which can be used in the sliding slewing bearing or the center plate of a bogie.

Microstructure and internal friction of Ni–Ti alloys absorbing hydrogen

The microstructure and internal friction of Ni–Ti alloys after hydrogen absorption have been investigated by means of optical microscopy, X-ray diffraction, differential scanning calorimetry and low frequency torsional internal friction apparatus. The results show that, after hydrogen absorption, the grains tend to be elongated, and the nucleation and growth of hydrides are mainly concentrated at the grain boundaries. In addition, a new phase ultimately identified as Ti2NiH0·5 phase forms after absorption of hydrogen. The hydrogen induced martensite promotes the emergence of a two-stage transformation. However, the growth of hydrides causes a reduction of the hydrogen induced martensite. The hydrides act as strong pinning points, resulting in a dramatic increase in the internal friction. In addition, the marked change of the internal stress, caused by the microscopic strain and the mismatching of the volumes, also improves the internal friction.