Strain Recovery Research Articles

Recovery and prognostic values of myocardial strain in acute anterior and non-anterior wall myocardial infarction.

To assess the recovery and prognostic values of myocardial strain using cardiac magnetic resonance (CMR)- feature tracking (FT) in acute anterior and non-anterior wall myocardial infarction. 103 reperfused patients after STEMI who underwent CMR at about 4 days (baseline) and 4 months (follow-up) were included, including 48 and 55 patients with anterior wall myocardial infarction (AWMI) and non-anterior wall myocardial infarction(NAWMI). CMR-FT analysis was performed using cine images to measure LV global radial, circumferential, and longitudinal peak strains (GRS, GCS, and GLS, respectively). Infarct size (IS) and microvascular obstruction (MVO) were estimated by late-gadolinium enhancement imaging. The primary clinical endpoint was the occurrence of major adverse cardiac events (MACE) after infarction. Patients with AWMI had higher IS, higher MVO, lower ejection fraction, and more significantly impaired CMR-FT strain values than patients with NAWMI (all p<0.05). Global strain significantly improved at 4 months (all p<0.01), especial in NAWMI. GLS was an independent predictor (odds ratio = 2.08, 95% confidence interval = 1.032-4.227, p = 0.04] even after adjustment for IS and MVO. The optimal cutoff of GLS was -7.9%, with sensitivity and specificity were 73.3% and 75.0%, respectively. In receiver operating characteristic analysis, IS remained the strongest predictor (area under the curve [AUC] = 0.83, p<0.01), followed by MVO (AUC = 0.81, p<0.01) and GLS (AUC = 0.78, p<0.01). CMR-FT-derived global myocardial strains significantly improved over time, especial in NAWMI. GLS measurement independently predicted the occurrence of medium-term MACE.

Microstructure characteristics and superelastic properties of novel Ti–Cr–Sn superelastic alloys

Microstructures, texture, lattice deformation strain, and superelastic properties of four kinds of near β type Ti–Cr–Sn novel superelastic alloys were systematically investigated, i.e., Ti-2.5Cr-8.5Sn, Ti-3.0Cr-7.5Sn, Ti-3.5Cr-7.0Sn, and Ti-4.0Cr-6.5Sn (at.%). All the alloys after the solution-treatment at 1273 K followed by water quenching consisted of equiaxed β single phase grains at room temperature in addition to athermal ω phase particles. Mechanical tests revealed the largest superplastic recovery strains (excluding elastic strain) of 4.0% in Ti-4.0Cr-6.5Sn alloy. This is partially due to the large lattice deformation strain ∼6.32% and its well-developed 112β⟨110⟩β texture component when tensile test exqmined along the rolling direction (RD). Moreover, up to 100 cyclic loading-unloading tensile tests revealed that both Ti-4.0Cr-6.0Sn and Ti-2.5Cr-8.5 Sn alloys maintained almost perfect and large shape recovery strain (including elastic strain) over 4.5% without any additional thermo-mechanical treatment. Besides, the starting stress for inducing martensitic transformation in Ti-4.0Cr-6.5Sn alloy kept higher than 200 MPa during the 100 cycles. Based on these superior superelastic properties, it is concluded that these Ti–Cr–Sn superelastic alloys become practical alternatives to replace Ti–Ni not only for biomedical applications but industrial applications.

Development of Fe-Mn-Si-Cr-Ni shape memory alloy with ultrahigh mechanical properties and large recovery strain by laser powder bed fusion

This work systematically studied the effect of volumetric energy density E on the densification, microstructures, tensile mechanical properties, and shape memory performance of a Fe-Mn-Si-Cr-Ni shape memory alloy (SMA) fabricated by laser powder bed fusion (L-PBF). An E of 90–265 J/mm3 is suggested to fabricate the Fe-Mn-Si-Cr-Ni SMA with minor metallurgical defects and a high relative density of above 99%. The increase in E can promote the formation of the primary γ austenite and the solid phase transformation from the primary δ ferrite to the γ austenite, which helps to achieve a nearly complete γ austenitic microstructure. The increase in E also contributes to fabricating the Fe-Mn-Si-Cr-Ni SMA with superior comprehensive mechanical properties and shape memory performance by L-PBF. The Fe-Mn-Si-Cr-Ni SMA with a combination of good ductility of around 30%, high yield strength of above 480 MPa, an ultrahigh ultimate tensile strength of above 1 GPa, and large recovery strain of about 6% was manufactured by L-PBF under a high E of 222–250 J/mm3. The good shape memory effect, excellent comprehensive mechanical properties, and low cost of Fe-Mn-Si-Cr-Ni SMAs, as well as the outstanding ability to fabricate complex structures of L-PBF technology, provide a solid foundation for the design and fabrication of novel intelligent structures.

Effect of ultrasound-assisted resting on the quality of surimi-wheat dough and noodles

In this study, the influence of ultrasound-assisted resting at different power on the rheological properties, water distribution and structural characteristics of dough with 50 % surimi as well as the texture, cooking and microstructure characteristics of the surimi-wheat noodles were investigated. Compared with the fermentation control (FC) noodles, the microstructure, cooking and texture characteristics of noodles (≤24.00 W/L) were significantly (p < 0.05) improved after ultrasonic treating. As the increasing of ultrasonic power, compared to FC, the creep strain, recovery strain, semi-bound water, and free sulfhydryl (SH) contents of surimi-wheat dough decreased at first and then increased significantly (p < 0.05). The α-helix and β-turn content of dough increased at first and then decreased after ultrasonic treatment, while the β-sheet was reversed. The surimi-wheat dough network structure was improved by ultrasonic treatment, with the densest and continuous pore size in 21.33 W/L, but the dough structure was broken and loose (>21.33 W/L), which consisted of the hardness, elasticity, chewiness, resistant and cooked quality of surimi-wheat noodles. This work elucidated the effect of ultrasonic power on the performance of surimi-wheat dough, and the optimal ultrasound power was obtained, thereby improving the nutritional properties and the quality of surimi-wheat noodles.

Thermo-mechanical deformation for thermo-induced shape memory polymers at equilibrium and non-equilibrium temperatures: Experiment and simulation

Experimental investigations on the mechanical deformations of thermo-induced shape memory polymers (TSMPs) at equilibrium temperatures and shape memory effects at non-equilibrium temperatures are conducted at different strain rates. It is found that the loading history conditions change the glass transition temperature, which is the nature of the change of shape memory effect. Meanwhile, temperature hysteresis is observed in stress freezing and strain recovery stages due to the varied temperature rate. The effect of the loading histories on the shape memory effect is reflected by introducing the temperature rate, strain rate, and deformation-dependent delay factors into the rubbery phase volume fraction. Based on the phase transition theory, a logarithmic rate-based viscoelastic-viscoplastic model is established at finite deformation. In this model, the viscoelastic rubbery phase is parallel with the viscoplastic glassy phase. Then, a frozen phase is introduced into the parallel model by changing its frozen volume fraction to reflect the storage/release of the deformation. Finally, the proposed model is validated by comparing the simulated rate-dependent mechanical deformation at equilibrium temperatures and shape memory effect at non-equilibrium temperatures with corresponding experimental results.

Large Biaxial Recovered Strains in Self‐Shrinking 3D Shape‐Memory Polymer Parts Programmed via Printing with Application to Improve Cell Seeding

AbstractTrapping of strain in layers deposited during extrusion‐based (fused filament fabrication) 3D printing has previously been documented. If fiber‐level strain trapping can be understood sufficiently and controlled, 3D shape‐memory polymer parts could be simultaneously fabricated and programmed via printing (programming via printing; PvP), thereby achieving precisely controlled 3D‐to‐3D transformations of complex part geometries. Yet, because previous studies have only examined strain trapping in solid printed parts—such as layers or 3D objects with 100% infill—fundamental aspects of the PvP process and the potential for PvP to be applied to printing of porous 3D parts remain poorly understood. This work examines the extent to which strain can be trapped in individual fibers and in fibers that span negative space and the extent to which infill geometry affects the magnitude and recovery of strain trapped in porous PvP‐fabricated 3D parts. Additionally, multiaxial shape change of porous PvP‐fabricated 3D parts are for the first time studied, modeled, and applied in a proof‐of‐concept application. This work demonstrates the feasibility of strain trapping in individual fibers in 1D, 2D, and 3D PvP‐fabricated parts and illustrates the potential for PvP to provide new strategies to address unmet needs in biomedical and other fields.

Analytical and numerical study of shape memory polymers as intervertebral discs under pure bending

Rupture of the elastic nucleus is one of the most critical challenges in total disc replacement (TDR). Smart polymers (SMPs) could be good candidates for TDR due to their unique properties such as self-healing, shape memory, adhesion control, adhesive capability and self-assembly. Herein, we investigate the behavior of SMPs as intervertebral discs (IVDs) under pure bending loading using analytical and numerical methods. For this purpose, the lumbar disc was considered as a cantilever beam and constitutive equation for pure bending mode using Euler-Bernoulli beam theory were developed in a full cycle of stress-free strain recovery. Numerical evaluation was performed to understand the effect of frozen volume fraction to determine the appropriate SMP for clinical evaluations. We conduct all analyses for the L4-L5 vertebral section because it is the most susceptible lumbar disc to damage. The numerical results show that SMPs with rescued frozen volume fraction are better representative for natural lumbar disc. Our results also indicate that SMPs that replace IVDs should be able to withstand at least 7.8° and 8.93° angle changes for pure bending and flexion-extension loads without any damage.

Rheological, morphological and swelling properties of dysprosium-based composite hydrogel beads of alginate and chitosan: A promising material for the effective cationic and anionic dye removal

An alginate (Alg) and Alginate-chitosan (Alg-Ch) based novel hydrogel beads were fabricated by ionotropic gelation method using trivalent lanthanide dysprosium (Dy3+) ion as crosslinking agent. The chemical components, morphology and viscoelasticity of the as-prepared hydrogels were characterized by Fourier transform infrared spectroscopy (FT-IR), field-emission scanning electron microscopy (FESEM) and rheology. The hydrogels beads with high content of Alginate were smooth but with increase in chitosan in the hybrid beads, significant macro-porous structure was observed by FE-SEM. The Dy-Alg beads possess higher viscoelasticity compared to Dy-Alg-Ch hybrid beads along with the higher breaking strain and structure recovery as revealed by rheology. However, the hydrogel beads of 1:1 and 2:1 Dy-Alg-Ch showed stable gel structure upto 80 °C in contrast to Dy-Alg or 1:2 Dy-Alg-Ch hydrogel beads showing stabilization effect of adding chitosan to Dy-Alg beads. The hybrid hydrogel beads (1:2 and 1:1) showed much better swelling compared to Dy-Alg hydrogel beads. The as-prepared beads with higher chitosan content showed significantly high adsorption of cationic dye Rhodamine B (RhB) whereas decrease in chitosan content favored the adsorption of anionic dye Fluorescein (Flu). The mechanism of adsorption process was evaluated by fitting adsorption data to kinetic models which reveals that adsorption of both the dyes involve chemisorption phenomena determined mainly by film and intraparticle diffusion in case of RhB and by multiple steps in case of Flu. The easy and fast fabrication, outstanding mechanical and stable properties indicated the hydrogel as a promising material for the wastewater treatment with cost- effective performance.

Genomically Informed Custom Selective Enrichment of Shiga Toxigenic Escherichia coli (STEC) Outbreak Strains in Foods Using Antibiotics

Shiga toxigenic Escherichia coli (STEC) have been implicated in major foodborne outbreaks worldwide. The STEC family of pathogens is biochemically diverse, and current microbiological methods for detecting STEC are limited by the lack of a universal selective enrichment approach and prone to interference by high levels of background microbiota associated with certain types of foods. A novel approach has been developed for the recovery of foodborne illness outbreak strains during outbreak investigations based on the analysis of whole genome sequence data of implicated clinical isolates to determine antimicrobial resistance (AMR) genes. The presence of certain AMR genes in STEC has been correlated with the ability to grow in the presence of a specific antibiotic, which can be used to supplement enrichment broths to improve the recovery of a target strain. The enhanced recovery of STEC strains with different AMR profiles from various food types (beef, sprouts, leafy greens, and raw milk cheese) containing high levels of background microbiota was demonstrated using AMR predictions for nine different antibiotics. This genomically informed custom selective enrichment approach increases the availability of analytical options and improves the reliability of food microbiological analyses in confirming food vehicles implicated in outbreak events and defining the scope of product contamination to support risk assessment and risk management actions.

Martensitic transformation and shape memory effect of Ni49.6Ti45.4Ta5 shape memory alloy

NiTiTa shape memory alloys (SMAs) exhibit higher corrosion resistance and much better X-ray visibility in comparison with NiTi SMAs. In this work, the martensitic transformation, microstructure, and shape memory effect (SME) of Ni49.6Ti45.4Ta5 SMA are studied. When solution-treated, the alloy undergoes a single-step B2 ↔ B19′ transformation upon cooling and heating, which is gradually shifted to lower temperatures because of thermal cycling. A martensitic microstructure with well-defined twin variants is observed which is beneficial for SME whereas the formation of (Ta, Ti)2Ni phases may deteriorate it. After an optimal thermomechanical treatment, the maximum recovery strain reaches up to 5.32% under a pre-strain of 7%.

4D forming shape memory component of Cu–13Al–5Fe alloy based on laser powder bed fusion of metal powders

High transition-temperature shape memory alloy (SMA) is widely used in aviation, aerospace and weapon fields. Using commercially available Cu, Al and Fe powders, Cu–13Al–5Fe alloy with high austenite transition temperature of 356–419 °C has been fabricated by laser powder bed fusion (LPBF) and a criterion for formulating the process parameters of LPBF based on the mixture of metal powders has been established. It is found that the LPBF can refine the structure, enhance the mechanical property and shape memory effect (SME). The structure of LPBF formed Cu–13Al–5Fe alloy under the quenched state is composed of tiny β′ martensite distributing in the matrix while the shape memory recovery rate can reach to 100% at the bending sample with 100°, and the shape memory recovery strain can reach to 1.08% under the 5% pre-strain by compressive test. Besides, the compressive stress and strain are 1240 MPa and 15.65% at room temperature. Compared with the arc-melted Cu–13Al–5Fe alloy under the quenched state, its shape memory recovery strain and recovery ratio are increased by 54.2% and 65%, respectively; and its compressive stress and strain are increased by 37.32% and 70.11%, respectively. Considering that, the work provides a criterion and a method for forming the component of Cu–Al–Fe alloy by LPBF based on the mixture of metal powders.

Influence of Long-Term Agar-Slant Preservation at 4 °C on the Recombinant Enzyme Activity of Engineered Yeast

Strain preservation to maintain stable vitality and the recombinant enzyme activity plays a crucial role in industrial fermentation. A Pichia pastoris strain is routinely stored at −80 °C in a glycerol vial and activated on an antibiotic-containing YPD agar plate before being used for fermentation. Alternatively, the activated strain should be preserved in the agar slant at 2~4 °C (low-temperature storage) for a short period before use. To maximize the utilization of the low-temperature storage for fermentation, we evaluated this method by observing the capacity of both the vitality and the recombinant enzyme activity of the strain at different preservation durations. We found that engineered yeast could be preserved by low-temperature storage for at least 30 months without losing its vitality and biomass enzyme activity by the end of fermentation and could be directly used for the seed cultivation of fermentation, which is more time-saving than strain recovery from −80 °C in a glycerol vial. Moreover, the antibiotic added to the agar slant could be omitted if the heterologous gene was integrated into the host chromosome. Our approach may greatly elevate the production efficiency of the strain.

Microstructure and Mechanical Properties of NiTi Shape Memory Alloys by Laser Engineered Net Shaping

Herein, NiTi alloys are prepared by laser engineered net shaping (LENS) technology. By exploring the mechanical properties and microstructures of NiTi samples under different laser powers, it is concluded that NiTi alloys with a laser power of 350 W have better tensile strength (783 MPa) and strain recovery rate (59.01%). In addition, the mechanical properties and microstructure of NiTi samples with a laser power of 350 W at different aging temperatures (400–800 °C) are also explored. It is found that NiTi alloys aged at 600 °C had better tensile strength (729 MPa) and strain recovery rate (92.85%). In addition, the phase‐transition temperature and endothermic enthalpy and exothermic enthalpy of the NiTi samples after thermal treatment increased, which is attributed to the formation of stable martensite (B19′) inside the NiTi samples after thermal treatment, and the type of internal NiTi phases structure change significantly. Thermal treatment can generate Ni4Ti3, NiTi2 precipitates, and martensite (B19′) with high density of dislocations inside the NiTi samples. Herein, it is showed that LENS can prepare NiTi alloys with excellent mechanical and structural properties by controlling the equipment parameters and aging temperature.

Microstructure, martensitic transformation and shape memory effect of novel Cu–Al-Ga based shape memory single crystals

In this study, the shape memory effect of novel iron-alloyed Cu–Al-Ga shape memory single crystals were reported for the first time. The microstructure, crystal structure, martensitic transformation and shape memory effect of Cu–10Al-6Ga (master alloy), Cu–10Al-6Ga-3Fe, Cu–12Al-4Ga-3Fe and Cu–14Al-4Ga-3Fe (wt.%) were investigated. All studied alloys consist of dominant martensite and fine bcc nanoparticles with richer Fe content and poorer Cu content except master alloy. The martensitic transformation start temperatures are 241.3 °C, 251.3 °C and 71.9 °C for Cu–10Al-6Ga-3Fe, Cu–12Al-4Ga-3Fe and for Cu–14Al-4Ga-3Fe alloys, respectively. For master alloy, the martensitic transformation disappears resulted from the precipitation of a large amount of α-Cu during heating. In addition, the shape memory effects clearly increase as a result of increase of the pre-strains. The Cu–14Al-4Ga-3Fe single crystal obtains a maximum shape memory effect of 6.8% with 100% strain recovery when 10% pre-strain is applied.

Tailoring phase transformation behavior, microstructure, and superelasticity of NiTi shape memory alloys by specific change of laser power in selective laser melting

In this study, NiTi shape memory alloys (SMAs) were fabricated by selective laser melting (SLM), and it is found that specific change of laser power (from 55 W to 70 W) was effective to tailor their phase transformation behavior, microstructure, and superelasticity. Results indicated that a minor increase of laser power made transformation temperatures increase significantly owing to the depletion of Ni and the formation of precipitates. The microstructure of SLM NiTi SMAs underwent the change from coarse grains to coarse together with ultrafine grains when laser power increased from 55 to 70 W. The superelastic responses demonstrated that SLM NiTi SMAs fabricated by specific laser power exhibited significantly different recovery strains. Specifically, SLM NiTi fabricated by 65 W showed stable phase transformation recovery strain, and obtained recovery strain of 3.91% at 1st cycle and only about 0.03% degeneration after 10 times cyclic compression. These outstanding stable recovery strains were ascribed to the coexistence of high-density dislocations formed in ultrafine grains and abundant nanoprecipitates interior of the grains, which impeded the formation of plastic deformation during loading effectively. These results make it possible to obtain the desired functional properties of SLM NiTi SMAs by specific change of laser power.

Balanced strength-ductility combination and good recoverable strain of Ni50.7Ti49.3 alloy fabricated by high scanning velocity in selective laser melting

Optimizing of process parameters such as high laser power combined with high scanning velocity during selective laser melting (SLM) is appropriate to the demand of high efficiency and high precision fabrication of NiTi alloys. However, the exploration in such process window is inexhaustive yet. In this work, SLM parameters of high laser power combined with high scanning velocity (180 W and 800–1400 mm/s) are adopted to manufacture defect-free Ni 50.7 Ti 49.3 alloy and the microstructure, martensitic transformation, mechanical and functional properties are studied systematically. The microstructure of SLM samples is composed of alternate coarse and fine columnar grains in different regions of molten pool. Unique square grain structure is formed in the top surface. Consequently, the prepared Ni 50.7 Ti 49.3 samples exhibit balanced strength-ductility combination with tensile strength of 804.6–870.0 MPa and ductility of 6.4–8.1%. Good recoverable strain of 3.4%–4.7% and recovery ratio of 83.1%–88.9% is achieved. Basically, the change in the recoverable strain for the prepared samples at different scanning velocities are discussed based on thermodynamics analysis. The findings in this work provide some insights into design and preparation of high-performance NiTi alloys by SLM. • A newly developed selective laser melting parameter window of high laser power combined with high scanning velocity was investigated. • Balanced strength-ductility combination with tensile strength of 804.6–870.0 MPa and ductility of 6.4–8.1% was achieved. • Alternate coarse and fine columnar grains in square grain structure postpone the crack propagation. • Strain recovery via superelasticity or shape memory effect was analyzed based on thermodynamics principle.

Puncture-resistant self-healing polymers with multi-cycle adhesion and rapid healability.

The structural design of self-healing materials determines the ultimate performance of the product that can be used in a wide range of applications. Incorporating intrinsic self-healing moieties into puncture-resistant materials could significantly improve the failure resistance and product longevity, since their rapidly rebuilt bonds will provide additional recovery force to resist the external force. Herein, we present a series of tailored urea-modified poly(dimethylsiloxane)-based self-healing polymers (U-PDMS-SPs) that exhibit excellent puncture-resistant properties, fast autonomous self-healing, multi-cycle adhesion capabilities, and well-tunable mechanical properties. Controlling the composition of chemical and physical cross-links enables the U-PDMS-SPs to have an extensibility of 528% and a toughness of 0.6 MJ m-3. U-PDMS-SPs exhibit fast autonomous self-healability with 25% strain recovery within 2 minutes of healing, and over 90% toughness recovery after 16 hours. We further demonstrate its puncture-resistant properties under the ASTM D5748 standard with an unbreakable feature. Furthermore, the multi-cycle adhesive properties of U-PDMS-SPs are also revealed. High puncture resistance (>327 mJ) and facile adhesion with rapid autonomous self-healability will have a broad impact on the design of adhesives, roofing materials, and many other functional materials with enhanced longevity.

Mechanically robust and highly elastic thermally induced shape memory polyurethane based composites for smart and sustainable robotic applications

AbstractIn the present study, polyurethane (PU) was prepared using a pre‐polymer (two‐shot) process with a novel phloroglucinol chain extender. PU nanocomposite was prepared by incorporating acid‐FMWCNTs in pristine‐PU. Polystyrene (PS) was functionalized with the nitro group through our previously reported method. The ternary blend composites (PU/PS‐NO2/FMWNTs) were prepared using acid functionalized multiwall carbon nanotubes (FMWCNTs) for enhanced properties and selectivity. Nitro‐functionalized‐PS/PU composite properties were compared with pristine‐PU and its blend composite. The structure of the pre‐designed PU polymer and its composites were confirmed by the FTIR and the degree of crystallinity and amorphous state was determined with XRD analysis. Excellent thermal stabilities were confirmed through a TGA thermogram with an increase in the loading amount of FMWCNTs. Excellent tensile strength 59.2 ± 2.6 MPa with 0.1 g loading amount of FMWCNTs with enhanced flexibilities was achieved. The significant change in surface morphologies and porosity suggested enhanced interaction (physical and chain entanglement) of FMWCNTs and nitrated‐PS with PU chain as the loading amount of filler increased. The resulted porous spongy cluster (as seen in SEM images) provides efficient shape recovery strain with excellent flexibility to the composite material without compromising repeatability. Almost 100% shape recovery was observed for all samples with repeated recoveries. The recovery time of PU nanocomposite observed is shorter than neat polyurethane and PU/PS‐NO2 blends because of their better conductive nature but causes brittleness, which can easily initiate a crack in the sample compared to a blended sample.

Health Consequences of the COVID-19 Pandemic among Health-Care Workers: A Comparison between Groups Involved and Not Involved in COVID-19 Care.

Health consequences have been reported among health-care workers (HCWs) exposed to COVID-19. Sweden chose to manage the pandemic with a lower and more equal long-lasting work strain and shorter periods of recovery than in other countries. Few studies have examined the health consequences among HCWs working in such conditions. This study compared the health consequences after the first wave of the COVID-19 pandemic between HCWs involved in the care of COVID-19 patients and other HCWs and between occupational groups working in COVID-19 care. Multinomial logistic regression and univariate general linear models were used to identify differences. The levels of depression, emotional and physical fatigue, sleep quality, and general health were measured 6 months after the onset of the pandemic in 3495 HCW employed in Sweden. HCWs directly involved in COVID-19 care reported significantly poorer sleep quality and higher scores on emotional and physical exhaustion than those not involved in such care. Health consequences did not differ significantly between different occupational groups involved in COVID-19 care except for specialist nurses/midwives. HCWs more frequently involved in COVID-19 care reported higher levels of emotional and physical fatigue and poorer sleep but less severe than those reported in more severely affected countries.

Anomalous Strain Recovery after Stress Removal of Graded Rubber.

Mechanical responses after the uniaxial deformation of graded styrene-butadiene rubber (SBR) with a gradient in the crosslink points in the thickness direction were investigated as compared with those of homogenously vulcanized SBR samples. The elongational residual strain of a graded sample was found to depend on the part with a high crosslink density. Therefore, it showed good rubber elasticity. After stress removal, moreover, the graded sample showed a marked warpage. This suggested that shrinking stress acted on the surface with a high crosslink density, which would avoid a crack growth on the surface. The sample shape was then recovered to be flat very slowly, indicating that the shrinking stress worked for a long time. This unique rubber elasticity, i.e., slow strain recovery with an excellent strain recovery, makes graded rubber highly significant.