Cyclic Bending Tests Research Articles

Cell Guiding Multicomponent Nanoyarn Tendon Scaffolds with Tunable Morphology and Flexibility.

Nanofibrous scaffolds are widely investigated for tendon tissue engineering due to their porous structure, high flexibility, and the ability to guide cells in a preferred direction. Previous research has shown that providing a microenvironment similar to in vivo settings improves tissue regeneration. Therefore, in this work, ingenious multicomponent nanoyarn scaffolds that mimic the fibrillar and tubular structures of tendons are developed for the first time through electrospinning and bundling nanoyarns followed by electrospinning of a nanofibrous shell around the bundle. Multicomponent nanoyarn scaffolds out of poly(ε-caprolactone) with varying porosity, density, and diameter were successfully produced by coelectrospinning with water-soluble poly(2-ethyl-2-oxazoline) as a sacrificial component. The diameter and fiber orientation of the nanoyarns were successfully tuned based on parameter-morphology models obtained by the design of experiments. Cyclic bending tests were performed, indicating that the flexibility of the multicomponent nanoyarn scaffolds depends on the morphology and can be tuned through controlling the number of nanoyarns in the bundle and the porosity. Indirect and direct cell culture tests using mouse and equine tendon cells revealed excellent cytocompatibility of the nanofibrous products and demonstrated the potential of the nanoyarns to guide the growing cells along the nanofiber direction, which is crucial for tendon tissue engineering.

High‐Performance Flexible MoS2 Transistors Using Au/Cr/Al/Au as Source/Drain Electrodes

Abstract2D transition metal dichalcogenides such as molybdenum disulfide (MoS2) are promising candidates for flexible electronics because of their bandgap tunability, high carrier mobility, and mechanical flexibility. However, flexible MoS2 field effect transistors (FETs) are typically faced with high contact resistance which is identified as a critical limiting factor to their potential applications. The present work successfully addresses this challenge by using Al contacts without any annealing process. It is found that the contact resistance is strongly coupled to the Al thickness, increasing the Al thickness is beneficial to reduce the contact resistance. The observed variation in the device electrical characteristics can be associated with the formation of the natural aluminum oxide (AlxOy) film at the interface. An ultrathin Au insert layer can further advance the device performance. An optimal contact resistance of 2.03 kΩ and an on/off current ratio of 1.57 × 109 can be achieved in the flexible MoS2 FETs using Au/Cr/Al/Au as source/drain electrodes. Furthermore, no apparent degradation in the device properties is observed under systematic cyclic bending testing with bending radii of 18 and 15 mm. The successful integration of Au/Cr/Al/Au source/drain electrodes into MoS2 FETs promises its potential application in flexible electronic devices.

Evaluation of cyclic fatigue and bending test for different Nickle-Titanium files.

To compare cyclic fatigue resistance and bending for three different nickel-titanium (NiTi) rotary files. A sample of 90 NiTi instruments size (25.06) was divided into three groups with 30 files in each: Race Evo files (FKG Dentaire, Switzerland); Tia Tornado Blue files (TiaDent Inc., Texas- USA); One Curve files (Micro-Mega, France). Then each group was subdivided into two groups with 15 files in each; a bending test was performed for one group, and a dynamic cyclic fatigue test at body temperature was performed for the other group. Files fractured by cyclic fatigue were randomly picked from all tested groups for Scanning Electron Microscopy (SEM) (Jeol, Tokyo, Japan). In addition, the test included measuring the broken part of the files tested using (Electronic Micrometre Calliper with LCD Screen, Inch and Millimetre Conversion, Adoric- Taiwan). Data were statistically analyzed using a one-way ANOVA with Tukey-HSD post hoc test. It was found that maximum load [gf] was less (meaning more flexible) in the group of Tia Tornado Blue with a statistically significant difference in comparison with Race Evo and One Curve. The number of cycles to fracture (NCF) in the Race Evo group was significantly higher than the groups of One Curve and Tia Tornado Blue. Within the limitation of the study, it could be concluded that Race Evo files were more resistant to cyclic fatigue fracture and Tia Tornado Blue files were more flexible compared to the other tested files.

Deacetylation-controlled chitin derivative imbedded WPU nanocomposite for highly powered and robust triboelectric nanogenerator

For effective triboelectric nanogenerator, it remains a major challenge to improve the intrinsic electron-donating properties of positive materials. We report a positive triboelectric nanocomposite material based on chitin, a biopolymer, embedded in a waterborne polyurethane matrix to improve the output performance, sustainability, and robustness of triboelectric nanogenerators (TENGs). This nanocomposite can increase the output performance via electron donating control through the deacetylation of chitin nanofibers. For the deacetylation of chitin, the exposed amine group can be an attractive electron donor combined with polyurethane, resulting in a higher output characteristic (210 V and 3.2 μA/cm2), as confirmed by Kelvin probe force microscopy measurements. Moreover, this nanocomposite film showed good sustainability (V/V0 = 85%) in a humid environment (85 RH%) owing to its hydrogen bonding with water molecules. The hybridized film exhibited excellent robustness (100,000 cycles of bending test, long-term stability test over 10,000 s) in two types of harsh mechanical environments. This flexible, robust TENG with a nanocomposite film can serve as a self-powered motion sensor for monitoring various human motions, such as contact pressure and sliding speed. Combined with a homemade sodium-ion potentiometric sensor, stable operation of the dehydration monitoring system was successfully demonstrated under sweating conditions.

Fatigue strength estimation of a CF/PEKK composite through self-heating temperature analysis using cyclic bending tests at 20 kHz

Very high cycle fatigue (VHCF) testing at conventional frequencies is highly time-consuming and unrealistic for large sample sizes. Though testing at ultrasonic frequencies can accelerate the testing, any undesirable thermal effect arising from testing at 20 kHz can cause significant heat generation in the specimens, increasing the likelihood of thermally induced failure. When mitigated, the temperature behavior during ultrasonic fatigue testing may conversely provide knowledge of the fatigue behavior of the composite. We study this hypothesis in this work by estimating the fatigue strength of a CF/PEKK composite through its temperature evolution during 3-point bending tests at 20 kHz with different cyclic load amplitudes. The fatigue strength of the composite was estimated using the temperature characteristics from an increasing cyclic amplitude test. This estimation was validated with four constant cyclic amplitude tests. Further, the estimation model was extended to different pulse–pause sequences by two constant cyclic amplitude tests. The results indicate a reliable and rapid method for fatigue life estimation as a material property. Finally, the criticality of the self-heating phenomenon during the non-stationary self-heating condition was evaluated.

An Experimental Approach to Assess the Sensitivity of a Smart Concrete

Structural health monitoring of concrete infrastructure is a critical concern for timely repair and maintenance. This study provides an innovative approach utilizing smart concrete integrated with multi-walled carbon nanotubes (MWCNTs) to enhance electrical conductivity. The smart concrete’s self-sensing capability is assessed through fractional change in electrical resistance (FCR) measured using a four-probe technique. Four-point bending and compressive tests explore the material’s response to cyclic and monotonic loads. Additionally, the impact of saturation levels on self-sensing sensitivity is investigated through compressive tests on varying saturation degrees. Remarkably, a substantial correlation between crack mouth opening displacement (CMOD) and FCR is observed during cyclic bending tests, where FCR increases significantly (from 0.019% to 154%) as CMOD rises from 0.004 mm to 0.55 mm. Digital image correlation (DIC) further validates CMOD measurements and their correlation with FCR. Moreover, this study reveals that amplitude of loading and degree of saturation have a significant effect on the self-sensing of the smart concrete. In saturated conditions, the self-sensing response of the material is insensitive to the mechanical strain, while with reduction in the saturation degree, a quasi-linear response is observed. To assess the sensitivity of the smart concrete, stress and strain sensitivities were evaluated, revealing a noteworthy enhancement of approximately 33% and 50% in stress and strain sensitivity, respectively, as saturation levels decreased. The self-sensing response of the material is very sensitive to the mechanical strain during monotonic loading and damage. These findings indicate the potential of smart concrete as a promising tool for comprehensive, real-time structural health monitoring for infrastructure during its entire life.

Biomechanical analysis of a novel screw system with a variable locking angle in mandible angle fractures.

Locking plates nowadays represent an important treatment in bone trauma and bone healing due to its strong biomechanical properties. The purpose of this study was to both computationally and experimentally validate a novel screw locking system by comparing it to another locking system from state-of-the-art and to apply it in an environment of a fractured mandible. FEA was used to test both systems prior to experimental tests. The systems were locked in the plate holes at 0°, 10°, 15°, and 20°. Cyclic bending tests and push-out tests were performed in order to determine the stiffness and push-out forces of both locking systems. Finally, newly designed locking system was implemented in mandibular angle fracture. Control locking system was biomechanically superior in push-out test, but with no greater significance. In contrast, the new locking system showed greater stiffness by 17.3% at the deflection angle of 20° in cyclic tests, with lower values for other deflection angles. Similar values were displayed in fractured mandible angle environment. Greater stiffness of the new locking system in cyclic loading tests, together with polyaxiallity of the new locking screw, could lead to easier application and improved biomechanical stability of the mandible angle fractures.

Additively manufactured flexible on-package phased array antennas for 5G/mmWave wearable and conformal digital twin and massive MIMO applications

This paper thoroughly investigates material characterization, reliability evaluation, fabrication, and assembly processes of additively manufactured flexible packaging and reconfigurable on-package antenna arrays for next-generation 5G/mmWave wearable and conformal applications. The objective is to bridge the technology gap in current Flexible Hybrid Electronics (FHE) designs at mmWave frequencies and address the challenges of establishing future design standards for additively manufactured flexible packages and System-on-Package (SoP) integrated modules. Multiple 3D printed flexible materials have been characterized for their electrical and mechanical properties over the 5G/mmW frequency band (26–40 GHz), and the inkjet printed interconnects on 3D printed Polypropylene (PP) substrates demonstrated excellent electrical and mechanical performance during a 10,000-time cyclic bending test over typical wearable flexible radii down to 1 inch. A proof-of-concept flexible on-package phased array with an integrated microfluidic cooling channel on 3D printed substrates was fabricated and measured, demonstrating pm 37^{circ } beam steering capability with efficient cooling. The proposed reconfigurable design and low-temperature fabrication approach using additive manufacturing can be widely applied to next-generation highly-complex on-demand FHE, flexible multi-chip-module integration, and on-package phased-array modules for 5G/mmWave wearable and conformal smart skin, digital twin and massive MIMO applications.

Characterisation of energy-dissipating mechanisms by Acoustic Emission technique during mechanical loading of Ti2AlC and Ti3AlC2 MAX phases: Influence of phase composition and porosity

Mechanical properties of two ternary carbides MAX phases (Ti2AlC and Ti3AlC2) were investigated under cyclic bending tests with coupled acoustic emission monitoring (AE). Results show significant differences in terms of observed microstructural changes associated to acoustic emission response. Influence of the proportion of MAX phases and the presence of porosity in the sample were studied. It was found that homogeneous proportions of MAX phases led to an increase of interfaces in the material and thus to lower mechanical properties, with a more acoustically active behaviour. Porosity was found to be a preferential site of initiation and propagation of cracks, leading to samples enduring slower but earlier rupture.

Flexible Thermoelectric Films Based on Bi2Te3 Nanowires and Boron Nitride Nanotube Networks with Carbon Doping.

Energy recovery and reuse, industrial waste heat, and thermal energy recovery and conversion in emerging electronic devices are topics of widespread interest. Flexible composite thermoelectric (TE) films have become the key to TE conversion, and many studies and synthesis methods related to them have made great progress. However, little research has been performed on the corresponding composites of typical TE materials with low-dimensional nanotubular materials, particularly modulation of the overall TE properties using doped low-dimensional nanotubular materials. In this work, high-quality bismuth telluride (Bi2Te3) nanowires and boron nitride nanotubes (BNNTs) were prepared using electrolytic deposition and high-temperature catalytic deposition, respectively. Bi2Te3-BNNTs composite films were prepared using a solvent hot pressing method. The Bi2Te3-BNNTs composite film conductivity reached 179.6 S/cm at room temperature (300 K), the corresponding Seebeck coefficient was 171.4 μV/K, and the power factor (PF) was 52.8 nW/mK2. Carbon doping of BNNTs resulted in carbon-boron nitride nanotubes (BCNNTs), and Bi2Te3-BNNTs composite films were prepared. The Bi2Te3-BCNNTs composite films obtained a conductivity of 4629.6 S/cm, at room temperature (300 K), a corresponding Seebeck coefficient of 181.2 μV/K, and a PF of 1520.0 nW/mK2. This study has important reference value for the application of TE conversion. Moreover, the electrical conductivity decreased by no more than 10% after 400 cycles of bending tests, and the electrical conductivity showed signs of recovery after repressing thermally, which undoubtedly proves that Bi2Te3-BCNNTs composite films have good flexibility and thermal stability, and this has contributed to the application and promotion of flexible thermoelectric materials.

塩化ビニル管の繰返し曲げ挙動

Many buildings have been reported to stop their service due to damage to non-structural members such as equipment piping after large-scale earthquakes. Although data on deformation capacity and strength of carbon steel pipe for ordinary piping is being collected, few studies are conducted on polyvinyl chloride pipes (PVC pipes) for drainage. Cyclic bending tests are conducted of PVC pipes with nominal diameters of 40A, 50A and 75A to evaluate their deformation capacity and strength. The result is that the deformation of PVC pipes is larger than that of steel pipes, and shows brittle failure.

Multifunctional superhydrophobic coatings for controllable self-propelled motion

Recently, multi-responsive actuators have attracted great attention, and it remains challenging to develop flexible and durable actuators with controllable motions on water surface. Here, a facile spray-coating method is proposed to fabricate superhydrophobic and multi-responsive acidified carbon nanotubes /Fe3O4/octadecylamine/polydimethylsiloxane (CFOP) coatings. The CFOP coating imparts the paper composite (CFOP@paper) with superhydrophobicity, self-cleaning performance, excellent photothermal conversion and magnetic properties. In addition, the strong interfacial adhesion between the coating and the paper ensures the surface stability and durability during cyclic bending and abrasion tests. The CFOP@paper can achieve controllable light-driven motion based on the Marangoni effect. The CFOP coating is also used for preparation of the superhydrophobic/superoleophilic sponge composite, and the controllable and fast motions of the sponge composite are realized by a contactless magnetic field, which can be used for high efficiency adsorption of oil on water surface. The multi-responsive coating exhibits promising applications in the field of flexible electronics, smart actuators, environmental protection, and so on.

Reliability Test of Inkjet-Printable Silver Conductive Ink

Inkjet printing is a promising technique for fabricating printed electronics. This technique acquires the utilization of conductive ink to form a fine and thin resolution conductive structure on a flexible substrate. The challenges are to design a stable conductive ink with a controlled properties to prevent nozzle clogging. Furthermore, a fine structure construction often demonstrated poor device performance due low mechanical durability. In this work, we have characterized morphology of the newly developed inkjet-printable nanosilver conductive ink (Mi-Ag) in our laboratory. The ink shows a stable colloidal ink zeta potential of-79.1 mV with nanoparticle size less than 100 nm properties has been tailored for compatibility with inkjet printing of conductive pattern on polyethylene terephthalate (PET) flexible substrate. It has been ascertained that the flexible electronic form factor affects the quality of the physical and electrical properties of printed pattern and the device performance. Hence, the bending test of the printed RFID patterns fabricated with different layer of thicknesses was investigated. Electrical properties of the samples were monitored by in-situ conductivity and resistivity measurement under cyclic bending testing. Pattern with thinnest layer of 1.31μm (1X) had the smallest electrical properties percentage drop (38.4%) at 12,000 bending cycles due to the fact that in thick layer, the interparticle network started to change during bending and became weaker due to the large amount of the particles in the dense printed layer. In contrast, printed device exhibited minimal increase in resistivity. Consequently the particle gap increased which allowed the movement of electrons, leading to the increased of electrical resistance. The device endurance characteristic is crucial to satisfy future design requirement of flexible electronic applications.

Flexible random laser with high optical stability in dye-doped SiC nanowires

Flexible random laser has potential applications in the areas of biosensing, display imaging, and micro-illumination due to their simple production, flexibility and small size. However, the variation of random laser properties during bending and stretching is not conducive to the integration and application in optoelectronic devices. It is still a pressing problem to obtain a flexible random laser with high stability, high brightness and low loss. Here, a flexible dye-doped random laser with high stability is created using silicon carbide (SiC) nanowires as the scattering medium. To investigate and compare the random laser properties under various bending and stretching degrees, bending times, and pump times, the laser emission data were statistically evaluated and analyzed. The flexible laser property presents excellent optical stability in wavelength, emission intensity, and peak width by bending and stretching ranging from 0% to 30%. The laser samples can withstand at least 200 cycles of bending tests and 30 min of nonstop pumping excitation, proving the system's high repeatability and optical stability. The emission stability and system characterization are studied with a scattering density variation model. With random SiC nanowires as scatters, there is nearly no change in the scattering medium density, thus, the mean free path of photons is not altered, resulting in the stable emission property of the flexible random laser. This study provides a novel approach for developing integrated random laser applications and realizing flexible and stable random lasers in optics and optoelectronics.

Titanium alloy fatigue strength and eigenfrequency stability

We conducted a study on fatigue in flat samples of the VT3-1 titanium alloy using “soft” cyclic beam bending tests. For this purpose, we developed an innovative electromagnetic test bench. The test bench's electromechanical system induces mechanical vibrations at a frequency that matches the eigenfrequency of the sample, ensuring that the cyclic load frequency remains constant. The electromagnetic force bends the sample while the elastic force unbends it, producing a quasi-sinusoidal cyclic load. Through our investigation, we determined the impact of this cyclic loading on both cyclic strength and durability. Our findings indicate that the VT3-1 titanium alloy possesses high resistance to fatigue and an endurance limit. Furthermore, we observed a low variability of the experimental fatigue resistance in relation to the approximating fatigue curve, suggesting the alloy has high structural stability. This finding indicates that the VT3-1 titanium alloy possesses high structural stability. To assess eigenfrequency stability, we subjected the alloy samples to cyclic tests, interrupting them at a reference number of 50 million cycles to evaluate changes in eigenfrequencies and stability under loads close to the fatigue limit. The results showed that the titanium alloy has a high level of eigenfrequency stability. Interruptions in cyclic tests resulted in jump-like increases in eigenfrequencies, which was not observed in continuous tests. Nevertheless, the total eigenfrequency deviations from the initial value at the end of the tests were similar in both cases

Graphene composite paper synergized with micro/nanocellulose-fiber and silk fibroin for flexible strain sensor

The fabrication of uniform and strong graphene-based conductive paper is challenging due to easy aggregation and poor film formability of graphene. Herein, on the basis of good dispersing effect of nanocellulose, high content graphene (50 wt%) composite paper with micro/nanocellulose fibers and silk fibroin (SF) was manufactured via simple casting method. The synergistic effects of cellulose microfibers (CMFs), cellulose nanofibers (CNFs) and SF result in the paper with ideal combination of flexibility, electrical conductivity and mechanical strength, where CNFs, CMFs and SF act as dispersing and film forming for GNPs, dimensional stability, and interfacial binding agents, respectively. Extraordinarily, by adding SF, graphene nanosheets are tightly coated on the surface of CMFs. The composite paper shows a tensile strength of 49.29 MPa, surface resistance of 39.0–42.1 Ω and good joints bend sensing performance. Additionally, it is found that CMFs can hinder the micro-cracks from propagating during the cyclic elbow bending test. The graphene-based conductive paper is helpful for the development of smart clothing wearable biosensing devices.

Cold Atmospheric Plasma-Assisted Direct Deposition of Polypyrrole-Ag Nanocomposites for Flexible Electronic Sensors

Conductive polymers and their composite materials have attracted considerable interest due to their potential applications in sensors, actuators, drug delivery systems, and energy storage devices. Despite their wide range of applications, many challenges remain primarily with respect to the complex synthesis and time-consuming manufacturing steps that are often required in the fabrication process of various devices with conductive polymers. Here, we demonstrate the novel use of cold atmospheric plasma (CAP)-assisted deposition technologies as a solvent-free and scalable approach for in situ polymerization and direct deposition of conductive polypyrrole-silver (PPy-Ag) nanocomposites onto the desired substrates under atmospheric conditions. In this study, a systematic approach with different precursor composition mixtures containing pyrrole as the monomer and AgNO3 as the photoinitiator was investigated to assess the effect of precursor composition on the final chemical, electrical, and mechanical properties of the PPy-Ag nanocomposite thin-film coatings which were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and cyclic bending tests. The characterizations indicated the possibility of fabricating PPy-Ag nanocomposite films with tunable degrees of polymerization and Ag nanoparticle loading by simply varying the percentage of AgNO3 in precursor composition mixtures. Finally, as a proof of concept, the potential use of the PPy-Ag nanocomposite films with different Ag nanoparticle loading percentages was assessed for humidity sensing by measuring their level of change in electrical resistance in the relative humidity range of 12-60%. It is envisioned that the developed CAP-assisted deposition technology can provide a new stepping stone toward scalable additive manufacturing of various functional nanocomposite films for different low-cost and flexible electronic applications.

Conducting polypyrrole-coated leathers

Conducting polymers are promising materials applicable as interfaces in various functional materials given they intrinsically possess electronic and ionic conductivity. Herein, a conducting polymer, polypyrrole (PPy) was explored for surface modification of three different leathers via in-situ oxidation of pyrrole in the absence and the presence of two stabilizing polymers, hydroxypropylcellulose and poly(N-vinylpyrrolidone). Colloidal dispersed PPy assemblies were formed with colloidal stabilizers along with PPy-coated leathers and hampered the formation of PPy precipitates that would otherwise contaminate the leather surface. The surface-modified bio-based composites were characterized by FTIR and Raman spectroscopy, and optical and scanning electron microscopy. PPy was deposited on collagen fibers on both sides of the leather. The thickness of the PPy layer varied between 24 and 200 μm. Mechanical properties of the leathers manifested themselves by the decrease in tensile strength and elongation at break after the modification process. Sheet resistances were in the range of 100–103 kΩ/sq with the highest values observed for materials modified in the presence of the polymeric stabilizers. Different sheet resistances were obtained for the top and bottom sides of the leathers depending on the surface finishing. Furthermore, the modified leathers were subjected to cyclic bending tests and the variation in their resistivity was studied. The conductivity and electroactivity of the modified materials may serve as guidance for the rational design of intelligent leathers in the footwear, as heating elements, and in energy storage.

Fundamental Investigations to Evaluate the Influence of Notching Processes on a Subsequent Cyclic Bending Process for the Production of Wire Cores

The production of wire cores by notch rolling and cyclic bending promises an ecologically and economically efficient manufacturing option for steel fibers. The paper at hand evaluates the influence of wire strips on cyclic bending by applying rolled wire strips of DP600 sheet metal (t0 = 0.8 mm) and a new cyclic bending testing tool. Analysis of material separation with varying parameters, rolling gap d and bending angle β, proves the interdependency of both process step, but indicates reduced adjustability of the notch rolling process. To enable better adjustability of the wire strip’s characteristics and analysis of their effects, wire strip production in the laboratory by notch stamping instead of rolling is aspired. The prior interaction analysis states the web height b, the notch angle α, and the hardening distribution as relevant wire strip’s characteristics to be replicated. Based on experimental analysis, an equivalent of notch rolling by notch stamping is deduced by considering the web height b identical for stamping and rolling, by adjusting the tool’s notch angle αt based on an equation considering geometric evaluations of α, and by taking advantage of the asymmetric hardening distribution of the outer notch which is comparable to rolled wire strip.

Mandrel Bend Test of Screen-Printed Silver Conductors

Abstract Flexible electronics are electronic devices and components that can be stretched, bent, twisted, and folded without losing their functionality. Flexible electronics is conformable, lightweight, easily tailorable, and low-cost, and thus, flexible electronics is increasingly being explored in health care, internet of things, automotive, aerospace, communication, safety, security, and food-related applications. Also, flexible electronics can now support increased functionality as well as various fabrication techniques. With an increased adaptation of flexible electronics, research is being conducted to better understand the failure mechanism of flexible electronics and thus improve their reliability and service life. In this paper, a cyclic mandrel bend test has been designed and carried out on printed conductors with PET and PI substrates. With the designed test apparatus, both tensile and compressive bend tests have been performed. Using a four-wire method, the resistance change of the printed conductors with different widths has been measured in situ under tensile and compressive loading conditions using mandrels with different radii. The results have been compared among different conductor widths, bending modes, and substrate materials. Besides, in situ SEM images have been taken to understand the failure mechanisms of the printed conductors. Based on the study, it is seen that there exists a direct correlation between the mandrel diameter, the damage in the printed conductor, and thus, the resistance change with cyclic mandrel testing. Also, it is seen that the damage under compressive bending mode is significantly lower than the damage under tensile bending mode.