Surface Mechanical Treatment Research Articles

Influence of Deep Rolling Process Parameters on Surface Residual Stress of AA7075-T651 Aluminum Alloy Friction Stir Welded Joint

Friction stir welding is most commonly used for joining aluminum alloy parts. After welding, residual stresses occurred in the welded joint caused by non-uniform cooling rate. Friction stir welding usually generates tensile residual stress inside the workpiece which affects the strength in addition to the fatigue life of materials. Compressive residual stress usually is beneficial and it can be introduced by mechanical surface treatment methods such as deep rolling, shot peening, laser shock peening, etc. In this research, deep rolling was used for inducing compressive residual stress on surface of friction stir welded joint. The residual stresses values were obtained from X-ray diffraction machine. Influence of three deep rolling process parameters: rolling pressure, rolling speed and rolling offset on surface residual stresses at the welded joint were investigated. Each factor had 2 levels (23 full factorial design). The statistical analysis result showed that the rolling pressure, rolling speed, rolling offset, interaction between rolling pressure and rolling speed, interaction between rolling speed and rolling offset were statistically significant factors, with the most compressive residual stress value approximately -391.6 MPa. The appropriated deep rolling process parameters on surface residual stress of AA7075-T651 aluminum alloy friction stir welded joint were 1) rolling pressure about 150 bar 2) rolling speed about 1,400 mm/min 3) rolling offset about 0.1 mm.

A Novel Approach to Improve Repair Bond Strength of Repaired Acrylic Resin: An in Vitro Study on the Shear Bond Strength.

To evaluate the combined effect of mechanical surface treatment with intermediate bonding agents (methyl methacrylate [MMA] and silane coupling agents) and ZrO2 nanoparticle (nano-ZrO2 ) addition to repair material on the shear bond strength (SBS) of repaired denture bases. Heat-polymerized acrylic resin was used to fabricate 130 cylindrical blocks (15 mm × 10 mm) and divided into a control group without treatment (C, n = 10), and 3 repair groups (n = 40/group) divided into specimens treated with alumina blasting alone (AB), specimens blasted with alumina combined with silane coupling agent (AB + SCA), or combined with MMA-based composite bonding agent (AB + MA). Treated groups were further subdivided according to nano-ZrO2 concentrations into 0 wt%, 2.5 wt%, 5 wt%, and 7.5 wt% added to repair resin powder. Repair resin monomer and polymer were combined and packed on the repair area and then placed in a pressure pot at 37°C for 15 minutes for polymerization. Shear bond test was performed using a universal testing machine. Scanning electron microscopy (SEM) was used to examine the effect of surface modifications on repair surfaces and to evaluate the topography of fracture surfaces. Tukey-Kramer multiple-comparison test was used to detect significant differences between groups (p ≤ 0.05). SBS (MPa) of specimens treated with alumina blasting and application of intermediate agents were significantly higher than the control group (p < 0.05), while no significant differences were found between AB and control group (p > 0.05). Nano-ZrO2 addition significantly increased SBS except for AB, and 5%, 7.5% MA (p > 0.05). SEM evaluation showed that alumina blasting created rougher and more porous surfaces, while SCA and MA reduced the irregularities and fissures. Application of bonding agents to repair surfaces after alumina blasting improved the repair bond strength and proved to be a possible new adhesive method for denture repair. Moreover, nano-ZrO2 addition in combination with surface treatment improved the repair bond strength.

Consequences of deep rolling on the fatigue behavior of steel SAE 1045 at high loading amplitudes

Near surface sample volumes play an important role in terms of safety and reliability of technical components especially in the case of fatigue loading. By applying mechanical surface treatment methods such as shot peening, deep rolling or laser shock peening, near surface layers can be tailored resulting in increased fatigue strength especially in the high-cycle fatigue regime. For higher loading amplitudes, increase in fatigue strength, however, is less pronounced and even detrimental consequences of deep rolling treatments have been observed. To identify the reasons for these observations, the cyclic deformation behavior of differently deep rolled, quenched and tempered sample conditions of steel SAE 1045 under high loading amplitudes has been studied and assessed with a focus on the stability of near surface residual stresses. Based on the results, it is shown that the residual stress relaxation behavior in deep rolled material conditions is strongly affected by the cyclic yield strength of each material state and, thus, is related to cyclic plastic deformation. Furthermore, residual stress stability and plastic strain depend on the stress amplitude and are closely related to each other.

Coupled Deformation and Diffusion Process at the Stainless Steel/Carbon Steel Interface in the Deformation Bonding Process

Cylindrical and surface-treated blanks were used to prepare stainless steel/carbon steel composite specimens at different temperatures. The coupled deformation and diffusion of materials at the interface were investigated by SEM and ultrasonic “C” scanning detection. The difference in the elongation of the two metals is shown to result in tearing at the interface in the deformation bonding process. Cracks are mainly located in a more readily expanding substrate and are more pronounced at lower deformation temperatures. With an increase in deformation temperatures, the bonding efficiency also increases significantly, but the diffusion layer thickness is basically the same. The bonding efficiency of composites can be greatly improved by mechanical surface treatment at normal deformation temperatures.

Effect of Sandblasting and Zirconia Primer Application on The Zirconia-Cement Shear Bond Strength (An in-vitro Study)

Aim: This study was carried out to evaluate the effect of two types of surface treatments; Sandblasting (Al2O3 110 m) and Zirconia primer (Z-Prime Plus) applicaition on zirconia-resin cement shear bond strength. Materials and Methods: 28 zirconia discs were specially constructed for this study by CAD-CAM machine of dimensions 10 mm diameter and 5 mm thickness. The discs were divided into two groups according to sandblasting surface treatment as the following: Group (I):14 zirconia discs without sandblasting and Group (II):14 zirconia discs after being subjected to sandblasting. These groups are subdivided into two subgroups each according to Z-Primer Plus application. Subgroup A: 7 zirconia discs without primer application and Subgroup B: 7 zirconia discs with primer application. Sandblasting was carried out to fourteen zirconia discs using 110 μm(Al2O3). Zirconia Primer (Z Primer Plus) was applied to 14 zirconia discs.28 composite discs were fabricated according to manufacturer’s instructions with dimensions 5mm diameter and 2.5mm thickness. Cyclic loading was done by 10,000 Cycle, frequency 1.6 Hz, Torque; 2.4 Nm and Weight 3 kg (30 N) and also thermocycling was done, at5oC and 55oC and number of cycles is 500 cycles. Testing shear bond strength was done for all samples using universal testing machine.Results: It was found that the highest shear bond strength mean value recorded for group (IIB) followed by group (IB) then group (IIA) while the lowest mean value recorded for group (IA) The difference between different surface treatment groups was statistically significant as revealed with one way ANOVA test (p 0.05) differences between {(IIB) and (IB)}, {(IB)and (IIA)} and {(IIA) and (IA) }.It was noted that during thermo-mechanical aging a total loss of two samples in group (IIA) and only one sample in group (IA) and their results recorded as zero so not indicated in mean value calculation. Conclusions: The bonding to zirconia is affected by mechanical and chemical surface treatments which are sandblasting and primer application.

Nickel Powders Modified Nanocoating Strengthened Iron Plates by Surface Mechanical Attrition Alloy and Heat Treatment

Nickel Powders Modified Nanocoating Strengthened Iron Plates by Surface Mechanical Attrition Alloy and Heat Treatment

Mechanical Surface Treatments of Ti-6Al-4V Miniplate Implant Manufactured by Electrical Discharge Machining

Mechanical Surface Treatments of Ti-6Al-4V Miniplate Implant Manufactured by Electrical Discharge Machining

Contemporary teaching of restoration repair at dental schools in Germany – Close to universality and consistency

ObjectivesTo identify potential changes in various aspects of teaching and to ascertain whether previously found inconsistencies in the teaching of criteria, indications and operative techniques for the repair of defective composite restorations at German dental schools have been resolved. MethodsA validated questionnaire was used to gain the information sought. It was sent to all dental schools in Germany (n = 30). Whenever possible, data were compared to previous studies conducted in 2000 and 2009. Statistical analysis was performed using Fisher’s exact tests (p < 0.05). ResultsTwenty-nine schools responded to the survey – a response rate of 97%. All respondents indicated positive experiences with the repair of restorations. The teaching of repairs in 2018 (90%) was found to be comparable to the findings from the 2009 survey (88%, p = 1.000), but significantly increased since the 2000 survey (50%, p = 0.006). Main reasons reported for teaching repairs are tooth substance preservation (97%) and reduction of pulpal damage (79%). Main clinical indications are marginal defects and secondary caries. When performing repairs, almost all dental schools were found to teach both mechanical and adhesive substrate surface conditioning. Marked variation was observed in the method of mechanical surface treatment, with air abrasion having gained widespread popularity. The average expected longevity of repairs was 7.4 ± 3.0 years. ConclusionsThe teaching of the repair of resin composite restorations is widespread in dental schools in Germany. Aspects of this teaching were found to be more consistent between dental schools than in previous surveys, albeit variation in operative techniques still exists. Clinical significanceGraduates from dental schools in Germany may be found to be well equipped with the knowledge and skills to perform repairs of defective resin based composite restorations in clinical practice.

Mechanical Characteristics of Non-nickel Shape Memory Alloy of Medical Appointment

New shape memory alloy (Ti-20Nb-10Ta-5Zr) for production of minimally invasive implantation medical devices (cava filter) was tested for static mechanical properties. The material for investigations was wires with different thickness before and after thermal treatment in various conditions and surface mechanical treatment. The structure was investigated on a scanning electron microscope and on a Auger spectrometer. High indicators of strength and ductility were noted. The mechanical treatment of the surface and annealing in vacuum best affect it.

Effect of deep cold rolling on mechanical properties and microstructure of nickel-based superalloys

Mechanical surface treatments are performed on aerospace components for fatigue life enhancement by introducing beneficial compressive stress profiles and material strengthening. This paper studies the influence of Deep Cold Rolling (DCR) on the residual stress distribution, work hardening and the microstructure modification of two nickel-based superalloys, IN100 and RR1000. Two different diameters (6.3 mm and 12.6 mm) of the rolling ball inserts were investigated in this analysis. The hardness and residual stresses at the subsurface after DCR were analyzed along the rolling and transverse directions. Electron BackScatter Diffraction (EBSD) technique was used to characterize the microstructure of the samples both qualitatively and quantitatively. The degree of work hardening of fine grain RR1000 after DCR was characterized using full width at half-maximum (FWHM) of the X-ray diffraction peaks and Grain Orientation Spread (GOS) profiles acquired by EBSD characterization. The results clearly indicate that deep cold rolling introduces compressive residual stresses as deep as 1 mm, with significant work hardening at the subsurface in the coarse grain IN100. DCR resulted in the grain refinement, increase in low angle grain boundaries and clustering of dislocation density around the carbides in IN100. Depending on the ball diameter, DCR of RR1000 induced compressive residual stresses up to 700 µm and work hardening till the depths of 400 µm. Additionally, severe deformation of grains occurred near the rolling surface. The larger diameter of the rolling ball resulted in high degree of work hardening and better residual stress distribution deeper into the materials.

Friction and Wear Analysis of Deep Rolled and Vibrorolled Specimens in Lubricated Contact

Deep rolling is an established mechanical surface treatment technology based on local plastic deformation of the surface layer. By these means, residual stresses, and strain hardening are induced into the surface layer as well as its surface structure is smoothed. Vibrorolling is a derivate technology of deep rolling characterized by sinusoidal rolling lanes. Due to process kinematics of vibrorolling the surface layer is incrementally deformed multiple times in different directions. As a result, a more intensive plastic deformation of the surface layer is achieved and potentially tribologically active surface structures are produced. To investigate and compare the effects of both surface treatment technologies on the tribological behavior of a processed component, a friction and wear analysis under lubricated conditions was conducted in this work. Friction and wear behavior of untreated, deep rolled, and vibrorolled specimens using a pin-on-cylinder tribometer was conducted. Hardness, roughness, and geometrical measurements of the wear traces were used to characterize the specimens. Additionally, qualitative assessments of the wear traces using scanning electron microscopy imaging were made. The measurements were performed before, during, and after the friction and wear analysis. Furthermore, contact forces between a tribometer pin and the workpiece were determined to analyze the development of contact shear stresses. Based on the conducted investigations, the effects of deep rolling and vibrorolling on the friction and wear behavior of the treated specimens are discussed and explanations for the observed phenomena are formulated in this work.

Microstructural and micromechanical investigations of surface strengthening mechanisms induced by repeated impacts on pure iron

Mechanical surface treatments based on repeated impacts are known to create a graded strengthening in-depth by the means of severe plastic deformation. However microstructural evolution mechanisms leading local progressive grain refinement and the resulting surface mechanical hardening are not yet fully understood. It is shown in this paper that micro-percussion testing represents an interesting case scenario to emulate conventional treatments such as shot peening and better characterize microstructural changes at local and global scales. For this technique, every impact is made at the same position by a rigid conical indenter, controlling the number, angle and velocity of each impact. The main issue of this work is as follows: (i) to describe the transformed microstructures by the means of SEM microscopy and EBSD mapping; (ii) to quantify the mechanical gradient in-depth using the micro-pillar compression testing; and (iii) to converge both descriptions to understand the mechanisms involved on the strengthening of refined structures. This coupled experimental analysis would reveal the influence of different strengthening effects as the Hall-Petch effect or the dislocation hardening. This investigation is carried out in pure α-iron.

Effect of ultrasonic nanocrystal surface modification on elevated temperature residual stress, microstructure, and fatigue behavior of ATI 718Plus alloy

Ultrasonic Nanocrystal Surface Modification (UNSM) is a mechanical surface treatment that induces large compressive residual stresses and near-surface microstructural changes in the material by using repetitive impacts at ultrasonic frequencies with a WC tip. In this study, we investigate the use of UNSM to improve the fatigue life of ATI 718 Plus (718Plus) at high temperature of 650 °C. UNSM induced severe surface plastic deformation which led to nano-sized crystallites, twins, and high dislocation density in the near surface regions, coupled with an increase in surface hardness and high magnitude of compressive residual stresses. This change in the near-surface microstructure remained stable at elevated temperatures. In addition, UNSM retained ∼−680 MPa near-surface residual stress (56% of its initial residual stress) even after 140 h exposure to 650 °C. The retained near-surface residual stresses and the stable microstructure from the UNSM increased the yield strength by ∼11% (∼105 MPa) and endurance limit by ∼8% (∼70 MPa) in corresponding tests at 650 °C. This improvement in fatigue life was attributed to near-surface microstructure changes, material hardening and high compressive residual stress induced by UNSM. The estimated crack growth rates were ∼60% lower for UNSM-treated 718Plus as compared with untreated material. The thermal-mechanical residual stress relaxation indicates the effectiveness of UNSM in improving the fatigue life of 718Plus at 650 °C.

Mechanical surface treatments to optimize the fatigue behavior of quenched and tempered high strength steels

The aim of this work is to maximize the fatigue life of an AISI 4340 steel (quenched and tempered at 200 °C) with a tensile strength of 2000 MPa. To do so, different shot peening treatments were studied. Some of these treatments used traditional steel shots made of cut wire, and others used ceramic shots made of zirconia (Zirshot Y 300), which had not been used in previous works and had to be completely characterized. Additionally, secondary peening treatments and grit blasting were applied with the objective of decreasing the surface damage induced by the previous treatment. To characterize both primary and secondary shot peening treatments, the surface topography of the samples was analyzed using a roughness tester and scanning electron microscopy (SEM). The compressive residual stress field induced by these treatments was measured with X-ray diffraction (XRD). Afterwards, fatigue behavior was studied by means of four-point rotating bending tests. Fracture surfaces were analyzed using SEM. The results showed that an optimum combination of surface treatments (primary + secondary) avoided the initiation of cracks in the surface of the specimens (typical characteristic of fatigue failure under bending loads). In these cases, crack initiation always took place beneath the compressive stress field induced by the treatments, in alumina inclusions that acted as stress concentrators. Furthermore, the size and distribution of these alumina inclusions (analyzed using SEM) allowed determining the steel threshold amplitude of the stress intensity factor, ∆Kth.

Transverse strength measurements of repaired acrylic resin modified with different surface treatments

Aim: the purpose of this study was to evaluate the effect of chemical and mechanicalsurface treatments on repaired acrylic resin in terms of transverse strength.Materials and methods: seventy acrylic specimens were fabricated and divided into7 groups according to kind of reinforcement materials. Thesespecimenswere cut inthe mid and a space of 3 mm was created. The repair was done with varioussurface treatments and specimenswere then subjected to loads till fracture. Datawere analysed and compared via ANOVA and Tukey tests.Results: the transverse strength of repaired acrylic resin had been influenced by thetype of surface treatment used.The repaired samples withglass fibers,stainless steelwire and monomerimproved significantly the bond strength than untreated group(P&lt;0.05).Statistically, there were significant differences between control groupand repaired groups (P&lt;0.05); and among all repaired groups (P&lt;0.05) withexception no significant differencesbetween fiber and monomer, and wire andmonomer groups (P &gt; 0.05).Conclusion:A combination of chemical and mechanical treatments has a significanteffect on transverse strengths. The repaired joints with monomer, wire, or glassfibers had significantly improved the strength of repaired acrylic resin.

Interfacial bonding between CFRP and mechanically-treated aluminum liner surfaces for risers

The bonding between metal and carbon fiber-reinforced polymer (CFRP) composites is important in structures such as composite risers. Surface treatment of the metal is required to improve the metal-composite bonding. In this study, the effects of two mechanical surface treatment methods on the bonding between carbon/epoxy composites and aluminum are studied. The treatment methods investigated are grit blasting and grooving. Mechanical tests are performed and the test results are used with finite element simulations to study the failure and damage mechanisms at the composite-metal interface. The mechanical response and damage propagation at the metal-composite interface are modeled successfully using surface-based cohesive behavior. The finite element simulations gave insight into the way that the grooving treatment method improved the composite-metal bonding.

Influence of pre-machining on the surface integrity after processing by mechanical surface treatment

The functional performance of workpieces is strongly influenced by the surface and subsurface properties which are affected and can be adjusted by manufacturing processes. The finishing process determines the final form and the surface roughness of a machined component. Nonetheless, the final surface integrity is a result of the total material modification along the whole process chain. Previous manufacturing processes affect the initial residual stress state and the work hardening in the subsurface layers. Furthermore, the resulting material modifications may vary depending on the initial or pre-machined material state. In this paper, the influence of pre-machining processes on the resulting surface integrity after mechanical finishing processes is analyzed. As finishing processes, deep rolling and so called “grind-strengthening” with varied process parameters are chosen. The initial material state is generated by heat treatment followed by pre-machining using three different processes: turning, grinding and electrochemical etching leading to strong variations in the surface-near properties. For the analysis of the influence of initial material state residual stresses as well as the shear stress were considered. Both processes, deep rolling and grind-strengthening, achieve comparable compressive stresses at the surface, whereby the residual stress states can deviate for constant parameters under variation of pre-machining. The residual stress depth profiles show a significant influence of the initial state for the grinding process but minor influence for deep rolling. The investigations contribute to a better understanding of mechanisms causing material modification during mechanical surface treatment and along the process chain.

Increasing fatigue performance in AHSS thick sheet by surface treatments

Advanced High Strength Steels (AHSS) have been widely applied in the automotive industry as an affordable solution for car lightweighting, mainly in parts subjected to crash requirements. Heavy duty vehicle (HDV) can also benefit from the expertise learned in cars, but parts must be designed considering fatigue resistance, especially on trimmed areas, and stiffness. Mechanical surface treatments, as blasting or shot peening, help increasing fatigue life of AHSS in trimmed areas and will allow weight reduction in HDV through gauge downsizing. The expected decrease in stiffness through thickness reduction can be improved by design changes. However, scarce information about the effect of mechanical surface treatments on AHSS are available. Thus, the aim of this work is to evaluate the increment in fatigue life of two different steel grades (350 MPa, and 500MPa of yield strength) in thick sheet by means of mechanical surface treatment – sandblasting. High Cycle Fatigue [HCF] tests were conducted at alternating load [R=-1]. Residual stresses were measured by an X-ray tensometry prior fatigue tests. Also the surface roughness [Rz] and form is measured using an optical non-contact 3D microscope. On the other hand, the fracture surfaces of the test specimens were observed via scanning electron microscope (SEM) in order to determine the crack initiation points. The evaluation of fatigue life in terms of SN curves is also discussed, analysing how the sandblasting process modifies the surface roughness and introduce compressive residual stresses on the external layer of the material. Both phenomena enhance the fatigue strength of the evaluated steel grades.

Influence of Mechanical surface treatment on the strength of mixed adhesive joint

Adhesive bonding is a promising joining technique in modern transport industries which provides for lightweight connection of dissimilar materials. However, available adhesive types have reached their limits in terms of durability and strength. A potential solution to this problem is the utilization of mixed adhesives. However, the influence of the surface preparation method on the performance of mixed adhesive joints has not been investigated thoroughly yet. The objective of this study is therefore to analyze such influence on the strength of mixed adhesive single lap joints. In this regard, five mechanical surface treatment methods were examined on aluminium alloy AA6082 using combinations of three different types of adhesives by means of static tensile tests. The results show significant increase in joint strength and ductility for DP 8005-AV138 compared to AV138 alone for sanding surface preparation. The roughness value in the range of Ra=1.7 to 3.1µm and Rm=36.5 to 44.60µm provide the highest shear strength.

Shear Bond Strength of Ceramic Orthodontic Brackets to CAD/CAM Provisional Materials: Influence of Surface Treatments and a Novel Adhesive System

Objective: To evaluate the effect of surface treatments and flash-free adhesive on the shear bond strength of ceramic orthodontic brackets to CAD/CAM provisional materials. Materials and Methods: Specimens (n=160) from each provisional material (CAD-Temp and C-Temp) were categorized into four groups according to the surface treatment methods: C (no surface treatment), HP (37% H3PO4), DB (mechanical roughening by diamond bur) and SB (mechanical roughening by sandblasting). Half of the specimens in each group were bonded to one of the maxillary central incisor ceramic brackets according to the used adhesive system: (APC PLUS or APC Flash-free). All specimens were 5000-times thermocycled before the shear bond strength testing (SBS). Data were analyzed using three-way ANOVA, Tukey’s multiple comparison tests. The adhesive remnant index (ARI) was also evaluated. The level of significance was set at 5% for all statistical tests.Results: C-Temp significantly recorded higher SBS than CAD-Temp (p<. 001). DB and SB groups utilizing flash-free adhesive significantly recorded higher SBS (P<. 05) compared to other groups in the tested materials. Higher ARI scores were recorded in CAD-Temp and flash-free adhesive.Conclusions: Bonding of orthodontic brackets to provisional restorations is a challenge for orthodontists in adult comprehensive cases that could be improved by an appropriate material, surface treatments, and adhesive system. Mechanical surface treatments and flash-free adhesive would enhance SBS of ceramic orthodontic brackets to CAD/CAM provisional materials. The higher ARI scores reported with CAD-Temp and flash-free adhesive reduces chair time for excess removal.