Thermomechanical Tensile Tests Research Articles

Stress induced martensitic transformation in NiTi at elevated temperatures: Martensite variant microstructures, recoverable strains and plastic strains

To shed light on the origin of the loss of functional properties of NiTi with temperature increasing above 100 °C, we have investigated stress induced martensitic transformations in nanocrystalline NiTi shape memory wire by thermomechanical tensile testing supplemented with post-mortem reconstruction of martensite variant microstructures in grains by nanoscale orientation mapping in TEM. The stress induced martensitic transformation generating recoverable transformation strain as well as plastic strain is not completed at the end of the upper stress plateau. The higher is the test temperature, the larger is the volume fraction of retained austenite as well as the plastic strain. The martensite variant microstructures in NiTi wire deformed up to the end of the stress plateau at 120 °C contain partially detwinned single domains of (001) compound twin laminate filling entire grains. It is proposed that the stress induced martensitic transformation proceeds via habit plane interface between austenite and second order laminate of (001) compound twins and that the martensite promptly reorients and deforms plastically by dislocation glide in the [100](001) slip system. When the wire is loaded further beyond the end of the stress plateau, the stress induced martensitic transformation continues and the martensite deforms plastically. It is concluded that the observed gradual loss of superelastic functionality of NiTi with increasing temperature does not originate from the plastic deformation of austenite, as widely assumed in the literature, but that it derives from the loss of resistance of the stress induced martensite to the plastic deformation under increasing stress.

Memory behaviour of polyester knitted fabric integrated with temperature-responsive shape memory polymer filament

The present article highlights a novel approach towards investigating the memory behaviour of shape memory filaments integrated into a knitted textile structure. This study is the first step to investigate the interaction behaviour of such smart materials within textile structures. This integration can further open vast possibilities in designing smart textiles with unique functionalities such as sensing and actuating. A shape memory fabric (SMF) was successfully knitted using shape memory filament and polyester yarn. A systematic investigation is carried out to quantify the memory behaviour of SMF by thermo-mechanical tensile test. The experimental results reveal excellent shape recovery ( R r) (>90%) and good shape fixity ( R f) (∼80%) at strains of 20% and 60%, and temperatures of 30°C and 50°C. Memory filament behaves differently in a fabric structure compared to its pristine state at different temperatures and strains, as confirmed by experimental results. Under various thermo-mechanical conditions, the cyclic test of SMF revealed almost complete R r with an improvement in R f.

에폭시 수지의 열 및 기계적 특성에 대한 Bridge Group의 영향

In order to obtain thermosetting epoxy resin, it is the prerequisite condition that the epoxy precursor must contain at least two epoxy groups. Thus, bridge group is needed to link the epoxy groups, and naturally, the chemical structure of the bridge group may also influence the thermomechanical performances of the cured epoxy resin. However, literature about the effects of bridge group on properties of cured epoxy is seldom published. To fill the gap, three model epoxy monomers containing different bridge groups have been synthesized from 4,4'-dihydroxydiphenyl, 1,1-bis(4-hydroxyphenyl)cyclohexane and bisphenol A in this work. After chemical structure confirmation, all of the monomers are cured by methylhexahydrophthalic anhydride (HMMPA), and the properties of the obtained cured network are evaluated by differential scanning calorimetry (DSC), dynamic thermomechanical analysis (DMA), tensile test and scanning electron microscope (SEM). The results show that bulky bridge group can effectively increase the glass transition temperature, enhance the tensile strength, and enlarge elongation at break of the cured epoxy resin.

Highly porous 3D sponge-like shape memory polymer for tissue engineering application with remote actuation potential

Shape memory polymers (SMPs) based on poly(ε-caprolactone) have been recently investigated in biomedical application field owing to their intrinsic biocompatibility, biodegradability and capacity to undergo shape deformation on exposure to external stimuli. Porous SMPUs prepared by electrospinning technique are usually 2D structures not appropriate for cell proliferation. In this study, an attempt has been made to manufacture a 3D SMP scaffold using self-assembly electrospinning and simultaneous photo-crosslinking. A detailed investigation disclosed that suitable crosslinking between SMP chains, conductivity of the solution, and concentration of components play major role in fabricating 3D scaffold. Gold nanoparticles (GNPs) of 10-nm diameter were impregnated in 3D porous structure to cause remote actuation by infrared irradiation or magnetic field application for further studies. Results of scanning electron microscopy and transmission electron microscopy showed a highly porous structure with uniform distribution of GNPs. Sponges had an average porosity of 93±1.8%, demonstrating super-high absorption capacity. Thermal characterization performed using DSC and TGA demonstrated that the switching temperatures of the shape memory composites were near to body temperature and the degradation temperatures of the scaffolds were high enough for thermal stability. Cyclic, thermomechanical tensile tests revealed that the 3D scaffolds had good shape-memory (SM) properties with strain recovery rates of 88–98% and strain fixity rates up to 97% (after the fourth cycle), when deformations were attenuated at the body temperature range. Cytocompatibility evaluation using NIH3T3 cells showed non-toxic behavior suggesting that the GNPs incorporated scaffolds could be employed as 3D scaffolds for bio-applications.

Constitutive modeling for the simulation of the superplastic forming of TA15 titanium alloy

Titanium alloy, TA15, has a high strength-to-weight ratio, high weldability, and superior creep resistance at high temperatures up to 550 °C. TA15 is difficult to deform, especially for forming complex-shaped large-scale web–rib components, due to its low plasticity, large inhomogeneous deformation and narrow processing window. The objective of this research is to model the superplastic mechanisms in TA15 alloy with equiaxed, fine grain structure, and applying the proposed constitutive model to investigate the maximum grid aspect ratio, that can be achieved in superplastic forming (SPF), for a TA15 sheet with an initial thickness of 1.2 mm. Thermo-mechanical tensile tests are conducted first to characterize the superplastic behavior of the material in the temperature range of 880– 940 °C and the strain-rate of 0.0005–0.01 s−1. A set of mechanism-based unified visco-plastic constitutive equations has been proposed and calibrated based on the results of stress-strain data. A gradient-based optimization method is applied for the calibration of constitutive equations. The constitutive model is incorporated into FEA code through creep subroutine to check the validity of the proposed material model against the experimental SPF test of a multi-box die. Predicted sheet thickness and thinning in a die entry radius region at the end of forming are examined in detail. Preliminary results show a good agreement between the computational and experimental results.

Bending shape memory behaviours of carbon fibre reinforced polyurethane-type shape memory polymer composites under relatively small deformation: Characterisation and computational simulation

Shape memory polyurethanes (SMPU) have been of great interest in biomedical applications because of their unique ability to recover a primary shape by external actuation. This advantage can allow for easy suture and minimum tissue damage caused by surgery. Since SMPU suffer from low stiffness and low strength, carbon fibres have been widely used to reinforce SMPU, and their shape memory properties have been investigated using thermomechanical tensile tests. In reality, however, bending situations are more common than tensile situations, such as human skulls. In this study, carbon fibre reinforced SMPU (CF/SMPU) composites were studied as promising cranial implants that can offer shape memory properties, shape flexibility and high strength. First, the basic properties of pristine SMPU and CF/SMPU composites were characterised, including glass transition temperature (Tg), the viscosity of SMPU, the morphology of CF/SMPU, and their tensile and flexural mechanical properties. Then, a new method using rheometer was developed to study the shape memory behaviours of SMPU and CF/SMPU with three-point bending under relatively small deformations (≤1%), including flexural stress during programming and cooling, and bending recovery force during shape recovery. Finally, due to the invisibility of recovery process that was conducted in an enclosed temperature-controlling chamber of rheometer, the finite element method (FEM) was used to simulate the bending recovery test. The results showed carbon fibres significantly enhanced the mechanical properties (Young's modulus and flexural modulus) of SMPU. In terms of bending shape recovery, compared to pristine SMPU, CF/SMPU composites obtained substantially higher flexural stress during programming and cooling processes, and larger, more stable recovery force during recovery. The FEM results consolidated the peak recovery force of SMPU and the continuously growing recovery force of CF/SMPU as the temperature increased. Our findings on the improved mechanical and shape memory properties can provide a solid foundation for the potential applications of CF/SMPU composites as cranial implants.

Finite element modeling and validation of springback and stress relaxation in the thermo-mechanical forming of thin Ti-6Al-4V sheets

In this work, a hot forming procedure is developed using computer-aided engineering (CAE) to produce thin Ti-6Al-4V sheet components in an effective way. Traditional forming methods involve time- and cost-consuming furnace heating and subsequent hot sizing steps. A material model for finite element (FE) analyses of sheet metal forming and springback at elevated temperatures in Ti-6Al-4V is calibrated and evaluated. The anisotropic yield criterion proposed by Barlat et al. 2003 is applied, and the time- and temperature-dependent stress relaxation behavior for elastic and inelastic straining are modeled using a Zener–Wert–Avrami formulation. Thermo-mechanical uniaxial tensile tests, a biaxial test, and uniaxial stress relaxation tests are performed and used as experimental reference to identify material model parameters at temperatures up to 700 °C. The hot forming tool setup is manufactured and used to produce double-curved aero engine components at 700 °C with different cycle times for validation purposes. Correlations between the predicted and measured responses such as springback and shape deviation show promising agreement, also when the forming and subsequent holding time was as low as 150 s. The short cycle time resulted in elimination of a detectable alpha case layer. Also, the tool surface coating extends the tool life in combination with a suitable lubricant.

Constitutive parameters identification based on DIC assisted thermo-mechanical tensile test for hot stamping of boron steel

Hot stamping of Boron steel is a thermal-mechanical and phase transformation coupled process. The reliable testing and parameter identification method of the constitutive behavior is crucial for accurate simulation on hot stamping. The imprecise strain and strain rate calibration due to the inevitable temperature gradient along the gauge length in the Gleeble tensile test has been a great challenge to the accurate description on constitutive behavior at elevated temperatures. In the present work, a novel design of grips is developed to flexibly regulate the length of Uniform Temperature Zone (UTZ) along the specimen gauge length. A system with new speckle preparation method and great optical anti-interference ability is developed for the accurate strain calibration at elevated temperature and high-speed deformation based on digital image correlation (DIC). The influence of the length of UTZ and the strain measurement methods on the accuracy of parameters identification is further investigated. The DIC based calibration method on full-field strain and strain rate makes the parameter identification more robust on the length variation of UTZ, that is, the identified parameters are nearly the same using different UTZ length of specimen. The appropriate UTZ length should be satisfied to prevent the ends of gauge length from blue brittleness and the undesirable end failure. The identified constitutive parameters are verified by comparison between simulation and experiments of the hot stamping hat-type parts. It shows that the newly developed DIC-based method is the most precise within the context of the tested approaches to determine constitutive parameters of hot stamping process.

Investigating the Roles of Crystallizable and Glassy Switching Segments within Multiblock Copolymer Shape-Memory Materials

ABSTRACTThe variation of the molecular architecture of multiblock copolymers has enabled the introduction of functional behaviour and the control of key mechanical properties. In the current study, we explore the synergistic relationship of two structural components in a shape-memory material formed of a multiblock copolymer with crystallizable poly(ε-caprolactone) and crystallizable poly[oligo(3S-iso-butylmorpholine-2,5-dione)] segments (PCL-PIBMD). The thermal and structural properties of PCL-PIBMD films were compared with PCL-PU and PIBMD-PU, investigated by means of DSC, SAXS and WAXS measurements. The shape-memory properties were quantified by cyclic, thermomechanical tensile tests, where deformation strains up to 900% were applied for programming PCL-PIBMD films at 50 °C. Toluene vapor treatment experiments demonstrated that the temporary shape was fixed mainly by glassy PIBMD domains at strains lower than 600%, with the PCL contribution to fixation increasing to 42±2% at programming strains of 900%. This study into the shape-memory mechanism of PCL-PIBMD provides insight into the structure-function relation in multiblock copolymers with both crystallizable and glassy switching segments.

Shape memory behavior of liquid-crystalline elastomer/graphene oxide nanocomposites

Liquid-crystalline elastomer (LCE) nanocomposites exhibiting shape memory properties were prepared by dispersing a chemically modified graphene oxide (GO) in a smectic, lightly crosslinked epoxy resin obtained by curing p-bis(2,3-epoxypropoxy)-α-methylstilbene (DOMS) with sebacic acid (SA). Chemical grafting of DOMS monomer on GO particle surface improved interfacial adhesion between the epoxy matrix and the filler. The obtained nanocomposite films were characterized in their phase behavior, morphological and thermal properties. Furthermore, their shape memory properties were analyzed through two-way thermomechanical cycling tests. The combination of the LCE liquid crystallinity and the efficient dispersion of functionalized GO resulted in toughened, highly oriented systems endowed with enhanced shape memory response. Incorporation of 0.15 wt.% GO resulted in a significant increase of spontaneous elongation and reduced actuation temperature during cycling thermomechanical tensile testing, demonstrating the potential of these systems as shape memory materials for sensors and actuators.

Effect of the thickness reduction of specimens on the limit strains in thermomechanical tensile tests for hot-stamping studies

Sheet metal formability under hot stamping conditions has been evaluated using a novel planar testing system developed previously, being used within a Gleeble machine. Nevertheless, the specimen design with the central recess was not standardised, and the thickness reduction was not applied to the dog-bone type of specimen for testing at the uniaxial straining state. In this paper, effect of thickness reduction of dog-bone specimens on limit strain measurement under hot stamping conditions is investigated, and two types of dog-bone specimens without and with central recess are presented. Thermomechanical uniaxial tensile tests were performed at various deformation temperatures and strain rates, ranging from 370–510 °C and 0.01–1/s, respectively, by using the developed biaxial testing system in the Gleeble. The distributions of temperature and axial strain along gauge region of the two types of specimen were measured and compared. The specimen with consistent thickness had a better uniformity of temperature and strain distributions, compared to that with thickenss reduction. Forming limits for both types of specimen were also determined using the section-based international standard method. It is found that the accuracy of the calculation of forming limits based on the use of specimen with thickness reduction was highly dependent on the selection of the stage of the deformation of the specimen.

A Novel Grip Design for High-Accuracy Thermo-Mechanical Tensile Testing of Boron Steel under Hot Stamping Conditions

Achieving uniform temperature within the effective gauge length in thermo-mechanical testing is crucial for obtaining accurate material data under hot stamping conditions. A new grip design for the Gleeble Materials-Simulator has been developed to reduce the long-standing problem of temperature gradient along a test-piece during thermo-mechanical tensile testing. The grip design process comprised two parts. For the first part, the new design concept was analysed with the help of Abaqus coupled Thermal-Electric Finite element simulation through the user defined feedback control subroutine. The second part was Gleeble thermo-mechanical experiments using a dog-bone test-piece with both new and conventional grips. The temperature and strain distributions of the new design were compared with those obtained using the conventional system within the effective gauge length of 40 mm. Temperature difference from centre to edge of effective gauge length (temperature gradient) was reduced by 56% during soaking and reduced by 100% at 700 °C. Consequently, the strain gradient also reduced by 95%, and thus facilitated homogeneous deformation. Finally to correlate the design parameters of the electrical conductor used in the new grip design with the geometry and material of test-piece, an analytical relationship has been derived between the test-piece and electrical conductor.

Strain measurement and error analysis in thermo-mechanical tensile tests of sheet metals for hot stamping applications

In order to conduct uniaxial tensile tests for hot stamping applications, tests are normally performed by using a Gleeble thermo-mechanical materials simulator so that rapid heating and cooling processes can be obtained. However, temperature gradients in a specimen tested on Gleeble are inevitable due to resistance heating principles and heat loss to grips and water-cooled jaws. In this research, a pair of purpose-built grips made of stainless steel with low thermal conductivity and significantly reduced contacting area for clamping, as well as a flat dog-bone specimen with maximised parallel length (80 mm) were designed, for the purpose of improving the temperature uniformity within the concerned gauge section area of the specimen. Uniaxial tensile tests on AA6082 were performed, after controlled heating and cooling processes, at constant deformation temperatures in the range of 400 ℃–500 ℃ and at constant strain rate in the range of 0.1–4/s, to simulate its hot stamping conditions. The digital image correlation system was adopted to enable strain distributions in specimens to be measured. The temperature distributions in specimens were investigated and an effective gauge length of 14 mm was specified accordingly to ensure temperature gradients less than 10 ℃ within it at all tested temperatures. True stress–true strain curves of AA6082 were obtained based on results of strain measurements along the defined effective gauge length and used to calibrate a set of advanced material model. Error analysis was carried out by using thermo-electrical and thermo-mechanical FE models on ABAQUS, in which the calibrated material constitutive equations were implemented via subroutines. The error of stress–strain curves of AA6082 measured based on the specified gauge length was investigated and quantified by analysing the distribution of axial strain and axial stress.

Characterisation of vulcanised natural rubber behaviour by monotonic and in situ cyclic X-ray scattering tests

The effect of curing and loading conditions on the mechanical response of natural rubber are investigated by monotonic and in situ X-ray cyclic tensile tests. Tests are conducted on four samples, which differ by vulcanisation conditions. Samples are subject to two strain rates (2.7 × 10− 3 s− 1 and 16.66 × 10− 3 s− 1), and numerous imposed elongation levels range from 450 to 900%. The coupling between the strain rates and the elongation levels on the stress softening evolution resulting from strain induced crystallisation is investigated. In situ thermomechanical tensile cyclic test is performed in order to withdraw the effect of the strain induced crystallisation on the maximum stress decrease. The experimental results analysis shows that an optimum vulcanisation condition (150°C, 30 min) enhances the hardening process in the monotonic loading due to the strain induced crystallisation. However, under optimum curing conditions, cyclic loading induces a large hysteresis loss, a high stress softening and a high degree of strain induced crystallinity. The material softening sensitivity is controlled by coupled effect of strain ranges and elongation levels. This panoply of experimental measurements present a key information for material parameters identification that are useful to predict the lifetime of engineering components made of natural rubber such as racks, laminated rubber bearings and tires.

Thermoplastic shape-memory polyurethanes based on natural oils

A new family of segmented thermoplastic polyurethanes with thermally activated shape-memory properties was synthesized and characterized. Polyols derived from castor oil with different molecular weights but similar chemical structures and a corn-sugar-based chain extender (propanediol) were used as starting materials in order to maximize the content of carbon from renewable resources in the new materials. The composition was systematically varied to establish a structure–property map and identify compositions with desirable shape-memory properties. The thermal characterization of the new polyurethanes revealed a microphase separated structure, where both the soft (by convention the high molecular weight diol) and the hard phases were highly crystalline. Cyclic thermo-mechanical tensile tests showed that these polymers are excellent candidates for use as thermally activated shape-memory polymers, in which the crystalline soft segments promote high shape fixity values (close to 100%) and the hard segment crystallites ensure high shape recovery values (80–100%, depending on the hard segment content). The high proportion of components from renewable resources used in the polyurethane formulation leads to the synthesis of bio-based polyurethanes with shape-memory properties.

Shape-memory properties of electrospun non-woven fabrics prepared from degradable polyesterurethanes containing poly(ω-pentadecalactone) hard segments

Microscaled non-woven fabrics with fiber diameters in the range 1.8–3.1μm were prepared by electrospinning from a chloroform solution of a degradable multiblock copolymer (PDLCL) consisting of crystallizable poly(ω-pentadecalactone) hard segments (PPDL) and poly(ε-caprolactone) switching segments (PCL). The surface morphology and microstructure of the non-woven fabrics were characterized by scanning electron microscopy, temperature-controlled scanning probe microscopy, wide angle X-ray diffraction (WAXD), and small angle X-ray scattering (SAXS). The microstructural analysis demonstrated that the rod-like domains of hard segment (PPDL) formed in the electrospun PDLCL fiber functioned as physical crosslinks. Cyclic, thermomechanical tensile tests showed that the electrospun PDLCL fabrics exhibited good shape-memory properties with strain recovery rates of Rr=89–95% and strain fixity rates of Rf=82–83% after the 2nd cycle, when small deformations were applied at clinically relevant temperatures.

Synthesis and characterization of elastic star shape-memory polymers as self-expandable drug-eluting stents

Elastic shape-memory polymers as self-expendable polymeric drug-eluting stents are developed for the first time, with good mechanical properties, fast self-expansion, and sustained drug release. Novel star block co-polymer PCTOPDs containing hyperbranched poly(e-caprolactone) (PCL) switching segment and poly(2-oxepane-1,5-dione) (POPD) hard segment were synthesized in high yield and characterized by NMR, GPC, DSC, tensile test and cyclic thermomechanical tensile test. PCTOPD containing 15–27 wt% POPD (PCTOPD-15–27) are found to be non-cytotoxic thermoplastic elastomers (Tm of 39–40 and 120–129 °C, eb of 908–1060%, σm of 12–20 MPa, and E of 60–91 MPa) with good shape-memory properties at 40 °C (Rf of 95–97%, Rr of 97–99%, and shape recovery time of 35 s). The stent made from PCTOPD-27 gives nearly full self-expansion at 37 °C within 45 s. The collapse pressure at a compressive strain of 30% is 1.7 bar. A stent containing 3.0 wt% paclitaxel releases 42% drug linearly in the first 9 days and 67% drug in 30 days with a slower but nearly linear release for the period of 10–30 days. The developed SMP-based drug-eluting stents might be useful in biomedical application such as the treatment of coronary artery disease.

Shape-Memory Properties of Electrospun Non-wovens Prepared from Amorphous Polyetherurethanes Under Stress-free and Constant Strain Conditions

ABSTRACTThe shape-memory properties of electrospun polyetherurethanes (PEU) non-wovens with a single fiber diameter of around 1 μm were explored. In uniaxial cyclic, thermomechanical tensile tests a dual-shape shape-memory creation procedure (SMCP) was applied and the shape recovery was examined under stress-free and constant strain conditions. The thermal properties of the electrospun PEU non-wovens were found to be similar to those obtained for bulk PEU samples, whereas the mechanical properties revealed differences with respect to the elongation at break (εb) at increased temperatures. Excellent dual-shape properties were achieved for the PEU non-wovens with a high shape fixity rate (Rf) and shape recovery rate (Rr). A significant higher recovery stress (σmax) was obtained under constant strain recovery conditions for the electrospun non-wovens compared to the bulk PEU samples, which might be attributed to the higher degree of orientation of the polymer chains in the microfibers. Therefore the influence of different (single) fiber diameters as well as the variation of the programming elongation εm and temperature Tprog on σmax is an interesting issue for future investigations.

Biodegradable and photocurable multiblock copolymers with shape‐memory properties from poly(ε‐caprolactone) diol, poly(ethylene glycol), and 5‐cinnamoyloxyisophthalic acid

AbstractBiodegradable and photocurable multiblock copolymers of various compositions were synthesized by the high‐temperature solution polycondensation of poly(ε‐caprolactone) (PCL) diols of molecular weight (Mn) = 3000 and poly(ethylene glycol)s (PEG) of Mn = 3000 with a dichloride of 5‐cinnamoyloxyisophthalic acid (ICA) as a chain extender, followed by irradiation by a 400 W high‐pressure mercury lamp (λ > 280 nm) to form a network structure. The gel contents increased with photocuring time, reaching a level of over 90% after 10 min for all copolymers without a photoinitiator. The thermal and mechanical properties of the photocured copolymers were examined by DSC and tensile tests. In cyclic thermomechanical tensile tests, the photocured ICA/PCL/PEG copolymer films showed good shape‐memory properties at 37–60°C, with both shape fixity ratio and shape recovery ratio over 90% at a maximum tensile strain of 100–300%. The water absorption of these copolymers and their rate of degradation in a phosphate buffer solution (pH 7.0) at 37°C increased significantly with increasing PEG content. The novel photocured ICA/PCL/PEG multiblock copolymers are potentially useful in biomedical applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Mechanically active scaffolds from radio‐opaque shape‐memory polymer‐based composites

AbstractThe formation of functional tissue is strongly dependent on biochemical as well as physical signals. A common approach in tissue engineering is the application of passive scaffold systems with fixed morphology and stiffness. In this paper, we explored whether mechanically active scaffolds, exhibiting self‐sufficient shape changes under physiological conditions, can be prepared from radio‐opaque shape‐memory polymer composites (SMPCs). The influence of different thermomechanical treatments on the kinetics of the shape change was studied. Radio‐opaque SMPCs were obtained by incorporation of barium sulfate (BaSO4) microparticles (up to 40 wt%) into an amorphous polyether urethane (PEU) via co‐extrusion technique. The shape‐memory properties of the composites were investigated by cyclic, thermomechanical tensile tests consisting of a specific shape‐memory creation procedure (SMCP), in which the programming temperature (Tprog) was varied, followed by recovery under stress‐free condition, enabling the determination of the switching temperature (Tsw). An almost complete recovery with shape recovery rate (Rr) values ranging from 88% to 98% was realized within a small temperature interval of ΔTrec ≈ 30°C for all composites, while Tsw was found to be close to the applied Tprog. The feasibility of actively moving scaffolds was demonstrated using model scaffolds, where originally square‐shaped pores were temporarily fixed in an expanded circular shape at different Tprog. We found that the kinetics of the shape change obtained under physiological conditions could be adjusted by variation of Tprog between 1 and 6 hr. Such radio‐opaque scaffolds could serve as model scaffolds for investigating the active mechanical stimulation of cells in vitro or in vivo. Copyright © 2010 John Wiley & Sons, Ltd.