Mechanical Thermal Cycling Research Articles

Characterization of microstructure and local mechanical properties of friction rolling additive manufactured Al[sbnd]Li alloy under repeated thermal–mechanical cycles

Deformation-based friction rolling additive manufacturing (FRAM) is a promising solid-state additive manufacturing (AM) approach for producing non-fusible, weldable AlLi alloys. Along with the thermal cycles of conventional AM methods, the materials deposited during FRAM are affected by the repeated force of a tool head. However, the effect of repeated thermal–mechanical cycles on the microstructure and mechanical properties of a deposited material remains unclear. This study attempts to develop mechanisms by characterizing the microstructure and local mechanical properties of FRAM-ed AlLi alloys, with different deposition heights and those that underwent a different number of thermal–mechanical cycles. A recrystallized microstructure is successfully obtained and fine equiaxed grains are observed in the deposited material without pores and cracks. The value of ultimate tensile strength (UTS) reaches 98–91% of the base metal from the top to bottom regions. Under repeated thermal–mechanical cycles (from the top to bottom region), the grain size increases from 2.0 μm to 6.5 μm. The texture strength and diameter of δ’ precipitate also increase, while the volume fraction decreases. Together, they lead to a decrease in local UTS and elongation, from 450.7 MPa to 415.1 MPa and from 10.4% to 6.3%, respectively. The relationship between thermal–mechanical cycles and microstructure established in this study provides the foundation for subsequent research on FRAM thermal balance and microstructure regulation.

Influence of Thermal and Mechanical Load Cycling on Fracture Resistance of Premolars Filled with Calcium Silicate Sealer

The aim of this study was to evaluate the aging effect of thermomechanical cyclic load on fracture resistance of lower premolars obturated with AH Plus and BioRoot RCS root canal sealers. Forty-eight single-rooted premolars teeth were instrumented with REVO-S files up to SU/0.06 taper. The teeth were randomly assigned into 2 main groups (n = 24) according to the selected two root canal sealers (AH Plus or BioRoot RCS). All teeth were obturated using matching gutta-percha. Each main group were further divided into 3 subgroups (A, B and C) (n = 8). Group A acted as the negative control group (non-Thermomechanical aging). Whereas Group B and C were subjected first to thermal variations in a thermal cycling machine (7500 and 15,000 thermal cycles), then two different dynamic loading periods namely 3 × 105 and 6 × 105 in a masticatory simulator with a nominal load of 5 kg at 1.2 Hz which simulate approximately 1 ½ and 3 years of clinical function respectively. The roots were decoronated and fracture resistance were measured using a universal testing machine. After thermal-mechanical aging, BioRoot RCS showed significantly higher fracture resistance (p < 0.05) than AH Plus. As the thermal-mechanical cycles increased both AH Plus and BioRoot RCS exhibited a significant decrease in fracture resistance (p < 0.05). It could be concluded that thermomechanical aging had a significant impact on the outcome of the fracture resistance of AH Plus and BioRoot RCS.

Comparison of sintered silver die attach failure between thermal shock test and mechanical cycling test

This paper compares the degradation of sintered silver (s-Ag) die attach between a thermal shock test (TST) and a mechanical cycling test to correctly understand the mechanism of s-Ag die attach failure in power module products during practical operation. A bar-shaped specimen is subjected to two types of four-point bending tests: a centered bending test for bending moment application and a shifted bending test (SBT) for shear force application. The crack path in the SBT is similar to that in the TST, which suggests that shear force has an important role in imitating the degradation and failure of s-Ag in the TST. The crack propagation speed per cycle in the TST is, however, about 4000 times faster than that in the SBT. The lifetime assessment period of the SBT is approximately 1400 times shorter than that of the TST. The difference in failure mechanism between the TST and SBT is discussed by using scanning electron microscopy of the fractured specimens.

Effect of microcrystalline cellulose on mechanical property and shape memory property of water-borne epoxy

PurposeThis paper aims to study the effect of microcrystalline cellulose (MCC) on the mechanical property and shape memory property of water-borne epoxy (WEP).Design/methodology/approachIn the present study, the MCC/WEP composites were successfully prepared by melt-blending, freeze-drying and hot-pressing. The mechanical property tests were performed using a tensile test instrument (Instron Corp, Norwood, Massachusetts, USA). dynamic mechanical analysis Q800 was performed to analyze the sample’s dynamic mechanics. The thermal–mechanical cycle tests performed on a thermal mechanical analysis (TMA) Q400 in dynamic TMA mode enabled to analysis of the shape memory properties of the MCC/WEP composites.FindingsThe results showed that the inclusion of 2 wt.% MCC led to significant improvements in tensile strength and modulus of the composites, with tensile strength increasing by 33.2% and modulus expanding by 65.0%. Although the inclusion of the MCC into WEP enhanced the shape memory property, the MCC/WEP composites still maintained good shape memory fixity and shape memory recovery ratio of more than 95.0%.Originality/valueThis study has a significant reference value for improving the mechanical properties of WEP and other water-borne shape memory polymers.

Influence of Resin Cements and Ceramic types on the Color Stability and Translucence of Laminate Veneers/ Influência dos Cimentos de Resina e Tipos Cerâmicos na Estabilidade da Cor e Translucidez das Facetas Laminadas

Objective: This study evaluated the color stability and translucence of resin cements in the fixation of ceramic veneers submitted to aging protocols. Material and Methods: Buccal faces of bovine incisors were planed up to dentin. Eighty ceramic veneers (1 mm) were prepared using two pressed ceramics (IPS e-maxPress and IPS e-maxZirpress, IvoclarVivadent). Before the initial color and translucence readouts (Vita EasyShade, VITA), the veneers were fixed with light (Variolink II, Ivoclar/Vivadent) or dual cured (Relyx U200, 3M ESPE) cements. The samples were submitted (n=10) to thermal mechanical cycling (1.200.000 cycles, 1,3Hz, 5°C/37°C/55°C); and no aging protocol (control). New color and translucence readouts were performed. The cement thickness was quantified by a double coordinate stereomicroscope (Nikon Measurescope) as a control of the study. Results: Data (3-way ANOVA, Tukey, p0,05) showed difference (p0.05) in the color change for both ceramics cemented with U200 with no aging protocol. In the other groups, there was no significant difference (p0.05). There was no difference for translucence regardless ceramics, cements, or aging protocol. Thermal mechanical cycling was not significant for optical changes of the ceramics tested. Conclusions: It was concluded that the color stability and translucence of ceramics with thickness of 1mm were not influenced by the cement when submitted to thermal mechanical cycling.

Microstructural characteristics and computational investigation on electron beam welded Ti-6Al-4 V alloy

A microstructural characterisation and computational modelling framework for simulating the coupled thermal-mechanical cycles with two different initial parent microstructures, and their impact upon the emerging microstructure features including β grain size and phase volume fractions during electron beam welding (EBW) of Ti-6Al-4 V (Ti64) alloy is presented. Ti64 plates (measuring 5.5 mm in thickness) with different thermal processing have been electron beam welded using differing process parameter sets. These experimental welds have been fully characterised to provide information on the effect that a prior heat treatment has upon the microstructural evolution caused by the EB welding. Microstructure characterisation was investigated using both light microscopy and scanning electron microscopy. The results from this microstructure characterisation have been used to identity physically-based parameters required for microstructure predictions.

The use of nanoadditives within recycled polymers for food packaging: Properties, recyclability, and safety.

Nanotechnology is considered a highly valued technology to reduce the current environmental problem that is derived from plastic accumulation. The need to recycle and reuse packaging materials is essential to create a sustainable society towards a circular economy. However, the reprocessing of polymers leads to the deterioration of their characteristic mechanical, optical, thermal, and barrier properties due to the degradation of their polymeric chains. When recycled polymers are reinforced with nanoadditives, aforementioned properties improve and their use in the circular economy is more viable. In this review, different types of nanoadditives and recent advances in the development of recycled polymer nanocomposites reinforced with nanoadditives will be presented. In addition, there is a description of two research topics of current interest, recyclability of nanocomposites and safety for food packaging applications. Recyclability of nanocomposites requires a study that includes the nature of the polymer matrix, the type of polymer and the concentration of nanofiller, the morphology, the presence of additives, and the conditions of the thermal-mechanical cycles. Finally, safety section is dedicated to clarify the migration process in nanoreinforced-recycled polymers in order to assess their safety for food contact applications.

Surface evolution analysis of CrxWyNz coatings on WC mold in glass molding process

The CrxWyNz coatings were synthesized on the cemented carbide (WC-8Co) by plasma-enhanced magnetron sputtering (PEMS). The detailed glass cylinder compression was tested for the molding performance of the coated molds in the precision glass molding machine (PGMM). This work examined the surface morphology evolution, elemental compositions and mechanical properties of the CrxWyNz coatings by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), nano-indentation tester and atomic force microscope (AFM). The results showed that with the increased W content in the CrxWyNz coatings, the nano-hardness and Young's modulus of the coatings increased, and the surface roughness of the coatings reduced. The contact zone had lower surface roughness than the non-contact zone because of inhibiting the oxidation reaction. The molded glass pressing on the surfaces of Cr27W24N49 and Cr18W28N54 coatings had relatively better light transmittance. Besides, the CrxWyNz coatings (18 ≤ x ≤ 27, and 24 ≤ y ≤ 28) exhibited better oxidation resistance, chemical inertness, and surface quality during thermal-mechanical cycles, more suitable for glass molding protective coatings. The work sheds light on the preparation and application of glass molding protective coatings.

Thermo-mechanical behavior prediction of shape memory polymer based on the multiplicative decomposition of the deformation gradient

During the service of shape memory polymer (SMP), the thermal-mechanical cycle is a necessary process. Meanwhile, the influence of the viscoelastic properties of SMP, such as rate-dependent behaviors, can not be ignored during the application. Consequently, a constitutive model based on the multiplicative decomposition of the deformation gradient is proposed in this work, which can clearly describe the viscoelastic behavior and capture the thermal-mechanical cycle process of SMP. By introducing the “phase transition” concept, SMP is assumed as a composite composed of glassy phase and rubbery phase, and the volume fractions of each phase vary with temperature. Furthermore, according to the different mechanical behaviors of the glassy phase and rubbery phase, two different constitutive structures that can describe the strain sensitivity of SMP are developed to represent the mechanical response. The developed model was verified by simulating a series of experiments, including strain sensitivity tests and thermal-mechanical cycle experiments.

Thermo-mechanical behavior prediction of particulate reinforced shape memory polymer composite

A micromechanics model based on thermal viscoelasticity constitutive relation is presented to investigate the thermal-mechanical behavior of particulate reinforced shape memory polymer composite (SMPC). Based on the thermomechanical constitutive relation assumption and linear elastic constitutive relation assumption, the effective properties of SMPC are studied by using a micromechanics method. Through analyzing the constitutive theories of polymer and multi-walled carbon nanotubes (MWCNTs), as well as the filling quality of particles, the generalized Maxwell model (GMM) combined with Mori-Tanaka theory is developed, and the thermo-mechanical cycle behavior of SMPC is studied emphatically. Moreover, a set of uniaxial tensile experiments, stress relaxation tests and thermal-mechanical cycle tests are performed to verify the developed model. Eventually, the developed model is validated using a simulated example and experiment to ensure its creditability.

The Effect of Different Bleaching Treatments and Thermal-Mechanical Cycling on the Shear Bond Strength of Orthodontic Brackets.

The aim of the present study was to compare the shear bond strength (SBS) of orthodontic brackets bonded to the enamel after at-home and in-office bleaching treatments. Sixty bovine incisors were subjected to initial color readings and then classified into three groups: CP (16% carbamide peroxide), HP (35% hydrogen peroxide), and C (control). After treatments, new color readout was obtained, and orthodontic brackets were bonded to the bleached area. Half of the samples of each group (n=10) were subjected to thermal-mechanical cycling (TMC) testing (1,200,000 cycles; 44.2 N; 2 Hz/s), whereas the other half were stored in distilled water at 37 °C for 24 h. Samples were subjected to the SBS test at a speed of 0.5 mm/min. The mean SBS was analyzed (two-way ANOVA, Bonferroni test, p<0.05), and the fracture patterns were classified as adhesive, cohesive, and mixed types. There was no difference (p>0.05) in SBS values between the samples subjected to TMC and the cycled samples in any group. Samples subjected to carbamide peroxide presented lower SBS (p<0.05) than the non-cycled ones. Enamel adhesive fractures were higher in the bleached groups than in the control group, which presented mixed fractures prevalence, regardless of whether it was subjected to TMC or not. Thermal-mechanical cycling was not significant for SBS of orthodontic brackets, but tooth bleaching was a factor.

Thermal and mechanical energy harvesting using piezoelectric ceramics

The field of energy harvesting has drawn an increased amount of interest due to the rapid development of wireless sensors and self-powered devices. Currently, there is limited information regarding the impact of coupling both thermal and mechanical excitations in a single material and its energy harvesting capabilities. This paper demonstrates the use of Lead Zirconate Titanate (PZT) as a coupled thermal and mechanical energy harvesting device. PZT ceramic was subjected to different thermal and mechanical loading conditions. Under pure mechanical cycling the sample consistently generated the least power output averaging less than 200 nW. An increase in power output was observed under mechanical cycling and higher temperatures. A peak power of 500 nW was seen under both, thermal cycling, as well as under coupled thermal-mechanical cycling. This study demonstrated the feasibility to harvest different waste energies from a single device.

Preparation of self-lubricating NiTi alloy and its self-adaptive behavior

NiTi alloys with different porosities were obtained by the Spark Plasma Sintering method. The two-way shape memory effect of NiTi alloys with good integrated performance was obtained by the thermal-mechanical cycling training, and it was used to endow NiTi alloy with the self-adaptive behavior. The results show that the porous NiTi alloys with excellent tribological performances and functional properties were obtained. With the storage of oil, the friction coefficient can decrease from 0.391 to 0.041. The self-lubricating mechanism is the formation of a fractionated thin film, and the main wear form is abrasive wear. The lubricating oil inside the specimens with self-adaptive behavior can be squeezed out or stored back, so as to accommodate the lubricating film for better lubrication.

Comparison of fatigue strength of interfacial cracks between molding resin and metallic substrate in a power module under thermal cycle test and mechanical cycle test

Comparison of fatigue strength of interfacial cracks between molding resin and metallic substrate in a power module under thermal cycle test and mechanical cycle test

Er:YAG pre-treatment for bonding of orthodontic bracket: 1 year of in vitro treatment.

ObjectiveThe aim of this study was to evaluate in vitro bond strength of metal brackets bonded with: total etch, total etch with erbium: yttrium aluminum garnet laser (Er:YAG) and self-etching adhesive systems, submitted to thermal-mechanical cycling, simulating 1 year of orthodontic treatment.Materials and methodsFor the study, 80 bovine incisors were randomly divided into 3 experimental groups (n=16 each): XT- acid etching + Transbond XT, XT/Er:YAG- Transbond XT associated with Er:YAG laser irradiation (λ=2.94 μm, 60 mJ, 10 Hz) and SEP- Transbond Plus Self Etching Primer. Samples were submitted to thermal-mechanical cycling, simulating 1 year of orthodontic treatment. Afterward, the shear bond strength test was performed in a universal test machine at a speed of 0.5mm/min. Samples were evaluated under a stereomicroscope and by scanning electron microscopy for analysis of enamel surface and adhesive remnant index. Data were analyzed using Kruskal–Wallis and Mann–Whitney (with Bonferroni correction) statistical tests.ResultsStatistically significant difference was observed between the groups studied (p<0.05). Groups XT and SEP showed the highest bond strength values, without statistical difference between them, while group XT/Er:YAG showed reduction in bond strength values. Higher frequency of adhesive failures between enamel and adhesive system was verified for groups XT and XT/Er:YAG.ConclusionThe conventional (XT) and self-etching (SEP) adhesive systems showed mean bond strength values, similar between them, whereas the previous application of Er:YAG laser promoted the lowest bond strength values.

Shape memory induced structural evolution of high performance copolyimides

ABSTRACTIn this work, two kinds of high temperature shape memory copolyimides were prepared and the shape memory cycles induced structural evolution of macromolecular chains was investigated in detail. The glass transition temperature (Tg) of poly(benzoxazole‐co‐imide) (PI1) and poly(benzimidazole‐co‐imide) (PI2) are 280 °C and 355 °C, respectively. The results show that PI1 could keep stable macromolecular chain structure under shape memory cycles and exhibit outstanding shape memory performance (Rf &gt; 98%, Rr &gt; 97%) under different stretch condition. Whereas, shape memory cycles induced orientation with more ordered macromolecular chains packing is formed for PI2 after several thermal mechanical cycles, which strongly affect physical crosslinking points, thermal mechanical properties as well as shape memory behaviors. The study on macroscopic property and microscopic structure evolution will promote a better understanding of the shape memory effect of polyimides and accelerate development of high performance polyimides for shape memory applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3858–3867

Effects of thermomechanical and thermocycling on the shear bond strength of brackets to bovine enamel bonded with conventional and self-etching adhesive systems

Several adhesive systems have been developed in the last decade. The aim of the current study was to evaluate the shear bond strength of orthodontic brackets bonded with conventional primers or self-etching primers, artificially aged by means of thermocycling and thermomechanical procedures.90 bovine incisors were used in the investigation. The roots were sectioned in the amelo-cementary junction. All samples were randomly divided in 2 groups ( n= 45), according to the primer used for bracket bonding. XT Group–hydrophobic conventional primer (Transbond XT, 3M unitek, Monrovia, Calif); SEP Group –self-etching primer (Transbond Plus SEP, 3 M Unitek, Monrovia, Calif). All specimens were bonded with XT Transbond resin adhesive (3 M Unitek, Monrovia, Calif). A Universal Testing Machine EMIC DL2000 (EMIC Equip. Sist. Ensaio Ltda., São José dos Pinhais, PR, Brazil) was used for the collection of the values of SBS resistance. The results of the current study were: (Prompt L-Pop 1.72±0.13 MPa; Clearfil SE Bond 1.75±0.19 MPa; FL Bond 1.71±0.22 MPa; One-Up Bond 1.77±0.14 MPa; XT Control 10.5±0.86 MPa). In conclusion: the number of cycles in thermal and thermo mechanical cycling did not influence shear bond strength values for any of the primers tested;SEP Transbond Plus showed the greatest values for bond strength of orthodontic brackets.

Evaluation of marginal gap at the composite/enamel interface in Class II composite resin restoration by SEM after thermal and mechanical load cycling (An in vitro comparative study)

This study compared in vitro the marginal adaptation of three different, low shrink, direct posterior composites Filtek™ P60 (packable composite), Filtek™ P90 (Silorane-based composite) and Sonic fill™ (nanohybrid composite) at three different composite/enamel interface regions (occlusal, proximal and gingival regions) of a standardized Class II MO cavity after thermal changes and mechanical load cycling by scanning electron microscopy. Materials and methods:Thirty six sound human maxillary first premolars of approximately comparable sizes were divided into three main groups of (12 teeth) in each according to the type of restorative material that was used: group (A) the teeth were restored with Filtek™ P60 and single bond™ Universal adhesive using horizontal incremental technique, group (B)the teeth were restored with Filtek™ P90 and P90 system adhesive using horizontal incremental technique and group (C) the teeth were restored with Sonic fill™ composite and single bond™ Universal adhesive using bulk technique.After specimens were stored in distilled water at 37°C for 7 days, all specimens were subjected to thermocycling at (5° to 55 °C), then submitted to mechanical load cycling (intermittent axial force of 49N and a total of 50.000 cycles). The specimens were observed under scanning electron microscope at (2000 X) to measure marginal gap width (the distance between the dental wall and the restoration) at occlusal, proximal and gingival regions in micrometer using Tescan software, version 3.5. Data were analyzed statistically by one way ANOVA test and least significant difference tests. Results:The results showed that the silorane-based posterior composite (Filtek™ P90) showed significantly the least marginal gap width at the occlusal, proximal and gingival regions after the application of thermal changes and mechanical load cycling in comparison to the two methacrylate-based posterior composite Filtek™ P60 (packable) and the Sonic fill™ (nano-hybrid). Sonic fill™ bulk fill composite that relied on the vibration concept to lower the viscosity of high filler loaded composite material showed significantly lesser marginal gaps width at occlusal, proximal and gingival composite/enamel interface regions in comparison with Filtek™ P60 (packable composite) using horizontal incremental technique. The silorane-based composite (Filtek™ P90) showed non-significant difference in marginal gaps width at the three different regions. While, both methacrylate based Filtek™ P60 and Sonic fill™ composite showed significantly lesser marginal gap width at the occlusal region in comparison with gingival regions. Conclusion: None of the low-shrinkage composite restorative materials tested in this study totally prevented micro-

Novel Wear Testing Apparatus to Investigate the Reciprocating Sliding Wear in Sheet Metal Forming at Elevated Temperatures

Hot stamping has gained increasing importance in the last years due to the introduction of High Strength Steels (HSS) to improve the strength-to-mass ratio of stamped components. Despite the advantages in terms of load decrease, springback reduction and increased formability, the elevated temperatures the tools are subjected to may determine severe thermal mechanical cycling, increased oxidation and wear, which influence the tools service life and the quality of the produced parts. In addition, the frictional behaviour is also changing with temperature, thus affecting the performance of the forming operation itself. In this paper a novel experimental apparatus suitable for reciprocating sliding wear tests at elevated temperatures is presented. It consists of a linear sliding guideway connected to an electrical actuator and equipped with a heating plate to heat metal sheets. A solid frame embeds a screw device used to apply normal load. Thermocouples placed both on the plate and on sheet sample are used to control temperature during the test. The machine is also equipped with two load cells to record the normal and the tamgential loads. The 22MnB5 high strength steel was chosen as reference material for the machine testing. The results showed the capability of the new equipment and the good stability of the mechanical and thermal condition during testing.

Electroactive shape memory effect of radiation cross-linked SBS/LLDPE composites filled with carbon black

The poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer and linear low-density polyethylene (LLDPE) were blended and irradiated by γ rays to prepare shape memory polymer (SMP). Different weight fractions of conductive carbon black (CB) were filled into SMP to form a novel electroactive shape memory CB/SBS/LLDPE composite. The CB reinforced radiation cross-linked SBS/LLDPE blends for the improvement of the mechanical weakness and conductivity of SBS/LLDPE bulk and for wide practical engineering uses. The electroactive shape memory CB/SBS/LLDPE composites were investigated by electrical properties, mechanical, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and electroactive shape memory effects. It is found that the tensile strength, storage modulus, and resistance against mechanical and thermal mechanical cycle loading in the developed composites increased due to the role of reinforcement of CB. The melting temperatures and volume resistance of the composites decreased with the increment of CB for excellent electrical conductivity of CB. The electroactive shape memory effects of developed CB/SBS/LLDPE composites were affected by CB weight fractions and applied voltage, while good shape recovery could be obtained in the shape recovery test. When the CB fraction is more than 5 wt%, full recovery can be observed after tens of seconds and shape recovery speed increased with CB fractions and voltage increasing. However, the shape recovery rate decreases slightly with increment of cycle times.