Mechanical Testing Machine Research Articles

A study on influence of sintering temperature, diameter and volume fraction of metal hollow spheres on the mechanical properties of metal hollow spheres composites

The structural parameters (the sintering temperature, diameter, and volume fraction of the hollow spheres) have a considerable influence on the mechanical properties of metal hollow sphere composites (MHSCs). Hence, the influence laws of the structural parameters on the mechanical properties of MHSCs possess certain research significance. To obtain these laws, MHSCs with different structural parameters were fabricated using a pressure casting method. Subsequently, the density of the MHSCs was determined through the direct measurement method. Meanwhile, X-ray diffraction and scanning electron microscopy were employed to conduct in-depth analyses of the phase composition and microstructure of the MHSCs. Additionally, the compression performance of the MHSCs was measured with the assistance of a universal mechanical testing machine. The analysis of the microstructure and phase composition results revealed that MHSCs consisted of γ-Fe, Al, Si, Fe₂Al₇Si, Fe₂Al₄Si, and Al₈Si₆Mg₃Fe phases, with the transition layer composed of the Fe₂Al₇Si phase. The results of the compression performance indicated that the compression performance of MHSCs increased with the rise of the sintering temperature and decreased with the increase of the volume fraction. However, as the diameter of MHS increased, the yield strength of MHSCs declined while the deformation strength of MHSCs increased. When the diameter of the MHSs was 2.55mm and the volume fraction was 40%, the compression performance of the MHSCs reached its optimum. At that point, the yield strength was 113.65±3.37 Mpa, and the average deformation strength was 81.26±5.45 Mpa.

Kirschner wire creates more microdamage than standard or acrylic drill bits in the rabbit (Oryctolagus cuniculi) femur.

Histologically evaluate damage to rabbit femur after the creation of bicortical 1.5-mm-diameter holes using a standard surgical drill bit, an acrylic drill bit, and a Kirschner wire (K-wire). 10 femora (5 pairs) from skeletally mature female intact New Zealand white rabbits were used. The bone diaphyses were divided into 4 locations, systematically undergoing each test (surgical drill bit, acrylic drill bit, K-wire, and intact control). Four pairs were drilled using a mechanical testing machine, and 1 pair was drilled by hand. Cross-sections of the bone were stained en bloc with basic fuchsin for undecalcified histological evaluation. Damaged bone was reported as a percentage of a standardized area and categorized by location (cis- or transcortex), drill contact (entrance or exit of the cortex), and total damage (both cortices). The drilling method (hand vs mechanical testing machine) had no effect on histologic damage, so results were analyzed by combining all data. The K-wire demonstrated the greatest area of cracks/damage compared to both standard surgical and acrylic drill bits, whereas no difference in damage was noted between the 2 drill bits for all variables. The K-wire and drill bits caused microdamage; K-wire drilling created more microdamage than drill bits. The rabbit bone cortex is thin and brittle relative to dogs and cats, leading to failure during and after fracture fixation. The clinical failure of rabbit bone is at least partially caused by drill bits or K-wires causing microcracks.

Ballistic Performance of Polycarbonate Plate Subjected to Truncated Cone Projectile

In the present study, a quasi-static compression test and impact test are carried out on a Polycarbonate plate with thickness of 2.66 mm and an effective diameter of 205 mm. The impact test is carried out on a pneumatic gun using a hardened truncated cone projectile of mass 25.8 g at different velocities. On the other hand, a servo mechanical universal testing machine with a 50 kN capacity is used to carry out the quasi-static compression test at a speed of 2 mm/min adopting an indenter of truncated nose shape. The Dynamic Enhancement Factor, or DEF, is computed as the ratio of quasi-static perforation energy to impact perforation energy. The measured DEF in the present study is compared with previously published results for metal and polycarbonate. Also local deformation of the plate after perforation is compared for both quasi-static test and dynamic test.

The primary stability of ultrashort residual proximal femur fixed with triangular fixation stem prosthesis: a comparative biomechanical study based on sawbones models.

Tumor resection near the proximal end of the femur and revision surgery of the distal femoral prosthesis may result in a very short bone segment remaining at the proximal end of the femur, known as ultrashort residual proximal femur (URPF). In this study, we propose a triangular fixation stem (TFS) prosthesis to improve the fixation of URPF. The aim of this research is to investigate the biomechanical properties of the TFS prosthesis and compare it with the conventional stem (CS) prosthesis through in vitro biomechanical experiments, providing preliminary biomechanical evidence for prosthetic fixation of URPF. A biomechanical study was conducted using Sawbones to explore initial stability. Twelve Sawbones were used to create a bone defect model, and prostheses were designed and fabricated to emulate TFS fixation and CS fixation structures. Axial compression and horizontal torsion experiments were performed on the fixed models using a mechanical testing machine, recording maximum displacement, maximum torque, and femoral strain conditions. Under an axial compressive load of 2800N, the overall displacement of the TFS group was 3.33 ± 0.58mm, which was significantly smaller than that of the CS group (4.03 ± 0.32mm, P = 0.029). The femoral samples of the TFS group demonstrated that the strain value alterations at the medial points 2, 3, 5, 6 and the lateral point 10 were conspicuously smaller than those of the conventional stem group (P < 0.05). Under torsional loads at levels of 1°, 3°, and 5°, the torques of the TFS group were 3.86 ± 0.69Nm, 3.90 ± 1.26Nm, and 4.39 ± 1.67Nm respectively, all of which were significantly greater than those of the CS group (1.82 ± 0.82Nm, P < 0.001; 2.05 ± 0.89Nm, P = 0.016; 1.96 ± 0.50Nm, P = 0.015 respectively). The TFS prosthesis improves fixation strength and reduces strain on the femur's proximal surface. Compared to CS fixation, it offers better resistance to compression and rotation, as well as improved initial stability.

FRACTURE MECHANISM ANALYSIS OF HIGH-DENSITY FIBREBOARD BASED ON DIGITAL IMAGE CORRELATION TECHNOLOGY

This paper analyses the scattering images of the bending deformation of high-density fibreboards based on the digital image correlation (DIC) technique, so as to study its mechanical deformation law. Three-point bending tests were carried out on fibreboards using a mechanical testing machine with a non-contact measuring system. The measured values of the displacements of the grid nodes in the region of interest (ROI) were combined with the Moving least squares (MLS) method to construct the strains of the high-density fibreboards at different loading forces, thus deriving the strain values of the fibreboards during the bending deformation process. To further analyze its force deformation mechanism, this paper used a portable electron microscope and scanning electron microscope to analyze the damage situation at the fracture damage, and at the same time, it verified that the constructed strain field model was accurate.

Why should a bioengineering lab have engineers and health professionals?

Through the description of the methodology of the development of a bite force measurement device it will be shown how interdisciplinary work of Engineers and Health Professionals bring enhance of life quality to general population. Bite force measurement is a reliable exam to check stomatognathic system (SS) conditions. In order to provide a reliable, low cost and do-it-yourself gnathodynamometer a Dentist joined Bioengineering Laboratory (LabBio) at UFMG. The development of a 3D printed resin structure was made using CAD/CAM and tested by means of FEM. A Carbon Nano Tube (CNT) extensometer developed at CTNANO at UFMG to capture the structure deformation were fixed in two geometries that showed good results in FEM simulation and will be tested in an EMIC universal mechanical testing machine (DL1000) equipped with a 1 kN load cell. The electrical response of the extensometers was monitored using a Keithley 2000 digital multimeter (Tektronix), connected to a computer and remotely controlled by a LabView application (View Point Systems), a data storage protocol in a SD card and in the clouds using IoT and an data acquisition system will be tested. In bench tests both geometries showed good results with deformation capturable from 40 N. Data was codified using an Arduino Nano and a program was developed for data acquisition and storage. The interdisciplinary work generates prototypes with promising results in bench tests. The fruit of the team work may generate a toll that improves life quality of population by allowing more people to be tested and lowering health costs.

Study on fatigue characteristics of red sandstone under extremely high stress in the hydro-chemical environment

To study the failure of red sandstone under extremely high stress during the service life of tunnels, an in-depth study was conducted on the mechanical properties of red sandstone under uniaxial loading and cyclic loading and unloading processes at different pH values using the AG-250kNIS electronic precision material testing machine and MTS815 mechanical testing machine. The results show that as the acidity and alkalinity increase, the peak stress under uniaxial loading decreases and the axial strain increases,The peak stress at failure is 9.40, 12.37, 7.18, and 5.36 MPa, respectively, accounting for 74.19%, 68.91%, 40.38%, and 36.21% of the uniaxial compressive strength; The number of cycles significantly decreases during cyclic loading and unloading fatigue failure, and the stress required for sandstone failure gradually decreases. The peak strength and elastic modulus of sandstone show a decreasing trend, indicating that the hydrochemical environment plays an accelerating role in rock degradation. During the cyclic loading and unloading process of sandstone, there is a continuous increase in dissipated energy and finally a sudden increase, the Ud/U and Ue/U ratios at the peak point of sandstone in the natural state are 0.399 and 0.601, respectively, while the overall elastic energy shows an increasing trend; and a damage evolution model was established based on dissipative energy, which can better describe the degradation process of red sandstone.

Effect of double quenching process on Microstructure and Properties of 20CrMoH Alloy Steel

Abstract This article investigates the influence of dual quenching process quenching temperature on the microstructure, hardness, and mechanical properties of 20CrMoH alloy steel through optical metallographic microscopy, Rockwell hardness tester, and universal mechanical testing machine. The results indicate that during the second quenching in the temperature range of 780-880 °C, with the increase of quenching temperature, the tensile strength of 20CrMoH steel shows a rapid increase trend, from 1250MPa to 1550MPa. At this time, the matrix structure gradually evolves from ferrite + bainite structure to bainite + martensite, which is also the main factor for its rapid increase in tensile strength; When the quenching temperature rises to above 850 °C, the influence of quenching temperature on the tensile strength decreases, and the tensile strength remains around 1550MPa. The secondary quenching temperature has little effect on the plasticity of the material. The overall reduction and elongation of the section under different quenching temperature conditions are at a similar level, with a reduction rate of 9% -12% and a stable reduction rate of 50% -60%, indicating good mechanical properties.

The effects of setup parameters on the measured kinetic output of cervical disc prostheses

Mechanical testing machines are used to evaluate kinematics, kinetics, wear, and efficacy of spinal implants. The simulation of "physiological" spinal loading conditions necessitates the simultaneous use of multiple actuators. The challenge in achieving a desired loading profile lies in achieving close synchronization of these actuators. Errors in load application can be attributed to both the control system and the intrinsic sample response. Moreover, the presence of friction in the setup can have an impact on the measured outcome. The optimization of setup parameters can substantially improve the ability to simulate spinal loading conditions and obtain reliable data on implant performance. In this study, a reproducible kinematic test protocol was developed to evaluate the sensitivity of the kinetic response (i.e., measured loads, moments, and stiffnesses) of a cervical disc prosthesis to several testing parameters. In this context, five ceramic ball and socket sample implants were mounted in a 6 DOF material testing machine and tested with a constant axial compressive force of 100 N in two motion modes: 1) flexion-extension (±7.5°) and 2) lateral bending (±6°). Parameters including rotation rate, slider friction, friction between the samples' articulating surfaces, and moment arm were considered to determine their effects on measured kinetic parameters. The sensitivity analysis indicated that all setup parameters except friction between the samples' articulating surfaces had a substantial effect on the results. The findings were then compared to predictions from a free body diagram to determine the optimal setup parameters. Consequently, the setup with the lowest rotation rate and employing passive sliders yielded results that were consistent with the free body diagram. This study demonstrated the significance of a comprehensive setup evaluation for reliable and reproducible testing of spinal implants, also for comparison between labs.

Study of ZnO nanoparticle-doped dental adhesives on enamels with fluorosis: Electron microscopy, elemental composition and shear bond strength analysis.

This study aimed to evaluate dental adhesives containing different concentrations of zinc oxide nanoparticles (ZnO-NPs) for their use in the treatment of dental fluorosis, observe the interaction of the adhesive on healthy enamel surfaces and with mild and moderate fluorosis, measure the adhesive strength and fluorosis, and determine the phosphorus (P) and calcium (Ca) content on these surfaces, as a reference for the potential use of this adhesive with ZnO-NPs for dental fluorosis treatment. Transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM) were used to characterise the ZnO-NPs and analyse the weight percentages of P and Ca in the enamel using X-ray energy dispersive spectroscopy (EDS) and the adhesive strength using a universal mechanical testing machine. FESEM characterisation revealed that the ZnO-NPs were less than 100nm in size, with quasi-spherical and hexagonal prism shapes. The synthesis of the ZnO-NPs was confirmed by TEM, revealing their hexagonal crystalline structure. The adhesive strength by the universal mechanical testing machine showed that the adhesive with a 3% wt. concentration of ZnO-NPs was better in the three groups of teeth, showing higher adhesive strength in teeth with mild (15.15MPa) and moderate (12.76MPa) fluorosis surfaces, and was even higher than that in healthy teeth (9.65MPa). EDS analysis showed that teeth with mild and moderate fluorosis had the highest weight percentages of P and Ca, but there were no statistically significant differences compared to healthy teeth and teeth treated with adhesives. Lay description: This study focused on testing a new dental adhesive containing small particles called ZnO nanoparticles (ZnO-NPs). This study aimed to demonstrate whether this adhesive with ZnO-NPs could be useful for treating dental fluorosis by improving its adhesion to teeth. One of the first objectives was to determine whether the dental adhesive could adhere better to teeth affected by mild or moderate fluorosis than to healthy teeth by measuring whether the levels of two important elements for healthy teeth, calcium (Ca) and phosphorus (P), were affected by the adhesive. The size and shape of the small particles and teeth with mild or moderate fluorosis were observed using scanning electron microscopy. The nanoparticles were small (< 100nm) and had specific quasi-spherical and hexagonal prismatic shapes. More damage to the enamel was observed in teeth with mild or moderate fluorosis than in healthy teeth. The adhesive strength test demonstrated that the dental adhesive with 3% ZnO-NPs had the best adhesion on all healthy conditions of teeth. It was particularly effective in teeth with mild or moderate fluorosis. Finally, the evaluation of the levels of P and Ca on the enamel showed that teeth with fluorosis had higher levels of these elements, but using the dental adhesive with ZnO-NPs did not change the levels of these elements significantly because the adhesive avoided greater detachment because of greater adhesion to these surfaces. In conclusion, adding these small particles to dental adhesives could be an option for treating teeth affected by fluorosis. It stuck well and did not affect the levels of the important elements in the teeth.

Fabrication of PVA-Silica Sol Wood Composites via Delignification and Freezing Pretreatment.

The efficient exploitation of planted fast-growing wood is crucial for enhancing wood resource utilization. In this study, the fast-growing poplar wood was modified by in situ impregnation through vacuum impregnation with polyvinyl alcohol and nano-silica sol as impregnation modifiers, combined with delignification-freezing pretreatment. The samples were characterized by FTIR, XRD, SEM, and the universal mechanical testing machine. The results showed that the wrinkle deformation and cracking of the wood blocks were greatly alleviated after the delignification-freezing pretreatment and the polyvinyl alcohol and nano-silica sol were successfully integrated into the wood. The resulting polyvinyl alcohol-silica sol poplar composites exhibited about 216%, 80% and 43% higher compressive strength with respect to delignified wood, natural wood and impregnated natural wood, respectively, thereby demonstrating superior mechanical properties and potential opportunities for value-added and efficient utilization of low-quality wood.

Effect of infill pattern on the mechanical properties of PLA and ABS specimens prepared by FDM 3D printing

Fused deposition modelling (FDM) is a three-dimensional printing technique which has become more popular and spreading in many fields. In this process, the molten thermoplastic is deposited layer by layer using a heated nozzle. Users can set the infill pattern to save the material and printing time. The main objective of this study is to investigate the tensile properties of polylactic acid (PLA) and Acrylonitrile butadiene styrene (ABS) tensile specimens with different infill patterns such as lines, tri-hexagonal and lightning. Further, the test specimens were prepared as per ASTM D638 using Ender 3D printer with varying infill patterns. The specimens were subjected to tensile tests in a mechanical tensile testing machine. It was observed that the specimens with linear infill patterns obtained higher tensile strength than the tri-hexagonal and lightning pattern infilled specimens. Later on, a microstructural study was examined on the fractured surface using scanning-electron-microscopy (SEM). It shows that the line pattern specimens have more uniform structure when compared to hexagonal and lightning pattern specimens.

Application of small punch test to estimate mechanical behaviour of SUS304 austenitic stainless steel

The small punch test with an application of a relatively small specimen has recently become a reliable material mechanics testing method. In this study, the small punch test is set up based on the conventional mechanical testing machine for SUS304 stainless steel to evaluate the mechanical properties of SUS304 steel at different displacement rates of the punch in quasi-static loading condition in the case of with and without heat treatment. Although heat treatment has an insignificant effect on the microstructure and hardness of the material, the mechanical properties of the material in the small punch test are greatly reduced after heat treatment. Both cases with and without heat treatment have a similar tendency for the rate - sensitivity of the applied force - displacement curve. A higher value of force is applied to obtain the same value of displacement at a low displacement rate in the stable plastic deformation zone. Meanwhile, the maximum value of applied force is higher at a higher displacement rate in the stage that initiation of crack might appear. In the examined range of displacement rate, a positive rate - sensitivity of displacement at the maximum force. Therefore, a correlation between equivalent fracture strain and fracture toughness of the material can be achieved.

Study on the microstructure and mechanical properties of W-wire/TiBe, ZrBe, and ZrTiBe alloy composites

The microstructure and mechanical performance of W wire/Ti70Be30, Zr65Be35, and Zr37.5Ti26Be36.5 alloy composites were investigated in this study using X-ray diffractometer, scanning electron microscopy, and mechanical universal testing machine. These composites were prepared through the melt impregnation method under optimized processing conditions. The results show that the compressive strength of the three composites is all above 2600 MPa. The Ti70Be30-W composites diffuse violently at the interface, the W-Ti phase is formed at the interface, and the cracks of the composites under the action of applied load show a stepped pattern. The Zr65Be35-W composite reacts violently at the interface, resulting in a W2Zr interfacial product, which adheres to the surface of the W filament and presents a continuous interfacial reaction layer. When subjected to external load, the crack will expand rapidly along the interfacial reactive layer. The addition of Ti in Zr37.5Ti26Be36.5-W composites effectively inhibited the W-Zr reaction, the interface reactant W2Zr disappeared, and the W-Ti interface product presented a discontinuous interfacial reaction layer on the surface of the W filament, and the material split under the action of external load, and the crack showed step-like propagation.

Evaluation of Strain Sensors Based on Poly(acrylonitrile-co-butadiene) and Polypyrrole Synthesized by the Diffusion Method.

In this study, the functionality of an elastomer composite material containing polypyrrole (PPy) as a stress sensor was evaluated. The material was prepared using the swelling method by diffusing the pyrrole monomer into the elastomer before polymerization. To achieve adequate diffusion, organic solvents with affinity for the elastomer were used. The resulting materials were characterized by scanning electron microscopy (SEM), surface electrical resistance, and thermal and mechanical properties for application as a stress sensor. The simultaneous change in electrical resistance and tension stress was measured using a digital multimeter with electrodes connected to the jaws of a universal mechanical testing machine. The influence of stress cycles on the piezoresistivity of the composite materials was investigated. The obtained PPy/NBR composite presented a good combination of electrical conductivity and mechanical properties. The strain at break remained with mild variation after coating with PPy.

Mechanical Properties of Aramid Fiber Fabrics and Composites Enhanced by Phthalic Anhydride Catalyzed with Anhydrous Aluminum Chloride

The surface modification of aramid fiber plain fabric (PPTA) was conducted through phthalic anhydride treatment and anhydrous aluminum chloride (AlCl3) catalysis, aiming to enhance the interfacial bonding strength between aramid fiber fabric and bisphenol A diglycidyl ether (DGEBA) resin. The surface morphologies and structures of PPTA fiber before and after modification were characterized using scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and X-ray diffractometry. The mechanical properties of the PPTA/DGEBA composite were evaluated using a universal mechanical testing machine. The results demonstrate that when the concentration of phthalic anhydride is 0.3 mol/L, the tensile strength, bending strength and interlaminar shear strength of PPTA/DGEBA composites reach the maximum value, which are increased by 17.94%, 44.18%, and 15.94% compared with the unmodified sample, respectively. After a 0.5-h catalytic modification, the PPTA/DGEBA composites exhibited significantly enhanced tensile strength, bending strength, and interlaminar shear strength, achieving respective increments of 32.28%, 24.91%, and 29.10% compared to the modified samples without catalyst addition. Moreover, the overall mechanical properties of the aramid fiber fabrics and composites were substantially improved, which are more suitable for structural applications.

Properties of epoxy resin matrix composites improved by silica sol‐activated hollow ceramic microspheres

AbstractSilica sol can activate the surface of hollow ceramic microspheres and improve the properties of composite materials by improving the interface between the microspheres and the epoxy resin. The group changes on the surface of microspheres were measured using infrared spectroscopy. The microspheres were observed with a scanning electron microscope. The density, water absorption, and mechanical properties of the materials were tested using scales and mechanical testing machines. The results showed that SiO2 and silane molecules were introduced on the surface of the microspheres after treatments. As the silica sol content increased, the slurry viscosity increased by 34.5%, the composite density increased by 5.8%, and the water absorption decreased by 35.8%. When the silica sol content was 25%, the flexural strength and compressive strength of the composites were 73.49 and 116.27 MPa, respectively, which were 37.8% and 23.6% higher than those of the untreated composites, and the mechanical properties became clearly improved. High mechanical properties enable the materials to be used in deeper ocean areas.Highlights Nanoparticles are introduced onto the surface of hollow microspheres. The activated microspheres can bind better to the silane coupling agent. Silane coupling agent assisted by silica sol improved interfacial bonding. Surface activation of microspheres improves the properties of composites.

Development and performance evaluation of a multi-functional mechanical testing machine

Development and performance evaluation of a multi-functional mechanical testing machine

Mechanical response of human thoracic spine ligaments under quasi-static loading: An experimental study

PurposeThis study aimed to investigate the geometrical and mechanical properties of human thoracic spine ligaments subjected to uniaxial quasi-static tensile test. MethodsFour human thoracic spines, obtained through a body donation program, were utilized for the study. The anterior longitudinal ligament (ALL), posterior longitudinal ligament (PLL), capsular ligament (CL), ligamenta flava (LF), and the interspinous ligament and supraspinous ligament complex (ISL + SSL), were investigated. The samples underwent specimen preparation, including dissection, cleaning, and reinforcement, before being immersed in epoxy resin. Uniaxial tensile tests were performed using a custom-designed mechanical testing machine equipped with an environmental chamber (T = 36.6 °C; humidity 95%). Then, the obtained tensile curves were averaged preserving the characteristic regions of typical ligaments response. ResultsGeometrical and mechanical properties, such as initial length and width, failure load, and failure elongation, were measured. Analysis of variance (ANOVA) revealed significant differences among the ligaments for all investigated parameters. Pairwise comparisons using Tukey's post-hoc test indicated differences in initial length and width. ALL and PLL exhibited higher failure forces compared to CL and LF. ALL and ISL + SSL demonstrated biggest failure elongation. Comparisons with other studies showed variations in initial length, failure force, and failure elongation across different ligaments. The subsystem (Th1 – Th6 and Th7 – Th12) analysis revealed increases in initial length, width, failure force, and elongation for certain ligaments. ConclusionsVariations of both the geometric and mechanical properties of the ligaments were noticed, highlighting their unique characteristics and response to tensile force. Presented results extend very limited experimental data base of thoracic spine ligaments existing in the literature. The obtained geometrical and mechanical properties can help in the development of more precise human body models (HBMs).

Effects of alpha-tocopherol antioxidant on fracture strength and adhesion of endodontically treated teeth restored after dental bleaching.

This study evaluated the effect of different concentrations of alpha-tocopherol in gel form on fracture strength, hybrid layer formation, and microtensile bond strength of endodontically treated teeth bleached with 40% hydrogen peroxide (H2 O2 ). Sixty bovine incisors were randomized into one of six groups (n=10 incisors per group) defined by the interventions carried out after endodontic treatment. In the control group, no additional intervention was carried out, while all teeth in the five intervention groups were bleached with 40% H2 O2 and subsequently treated with alpha-tocopherol at concentrations of 15% (15AT), 20% (20AT), or 25% (25AT), with 10% sodium ascorbate (10SA), or with nothing (40HP). Fracture strength was evaluated in a mechanical testing machine, hybrid layer formation was assessed using scanning electron microscopy, and bond strength was determined using microtensile bond-strength testing. Data were analyzed using Kruskal-Wallis and Dunn's tests. No statistically significant difference regarding fracture strength was observed among groups. Hybrid layer formation was greater in the 15AT group than in groups 40HP and 10SA. Teeth in groups 15AT, 20AT, and 25AT demonstrated higher bond strength than teeth in groups 40HP and 10SA. Alpha-tocopherol, preferably at 15%, effectively reverses the deleterious effects, of bleaching, on hybrid layer formation and bond strength to dentin.