Surface Strain Distribution Research Articles

Blast response of full-size concrete walls with chemically reactive enamel (CRE)-coated steel reinforcement

In this study, two full-size concrete walls were tested and analyzed to demonstrate the effectiveness of a chemically reactive enamel (CRE) coating in improving their mechanical behavior under blast loading: one with CRE-coated rebar and the other with uncoated rebar. Each wall was subjected in sequence to four explosive loads with equivalent 2, 4, 6-trinitrotoluene (TNT) charge weights of 1.82, 4.54, 13.6, and 20.4 kg. A finite element model of each wall under a close-in blast load was developed and validated with pressure and strain measurements, and used to predict rebar stresses and concrete surface strain distributions of the wall. The test results and visual inspections consistently indicated that, compared with the barrier wall with uncoated reinforcement, the wall with CRE-coated rebar has fewer concrete cracks on the front and back faces, more effective stress transfers from concrete to steel rebar, and stronger connections with its concrete base. The concrete surface strain distributions predicted by the model under various loading conditions are in good agreement with the crack patterns observed during the tests.

Surface strain distribution of orthodontic miniscrews under load.

Our objective was to investigate surface strain around orthodontic miniscrews under different orthodontic loading conditions in simulated supporting bone. Thirty miniscrews with lengths of 6, 8, and 10mm were embedded into customized composite analog bone models. All miniscrews wereinserted into the simulated test bone 6mm deep and loaded with the same force of 200cN, creating different tipping moments at the peri-implant bone surface. A digital image correlation technique was used to measure the resulting surface strain around the orthodontic miniscrews. Changing the tipping moments is directly related to the strain generated at the bone surface close to the miniscrews, with greater moments creating greater maximum principal strains. Within the limitations of this model, it can be stated that greater tipping moments of miniscrews create greater maximum principal strain values, which have the potential to increase bone turnover around the implant. Hence, miniscrews farther from the bone surface should be loaded with less force, whereas miniscrews loaded closer to the bone surface may sustain higher forces.

Application of digital volume correlation to study the efficacy of prophylactic vertebral augmentation

BackgroundProphylactic augmentation is meant to reinforce the vertebral body, but in some cases it is suspected to actually weaken it. Past studies only investigated structural failure and the surface strain distribution. To elucidate the failure mechanism of the augmented vertebra, more information is needed about the internal strain distribution. This study aims to measure, for the first time, the full-field three-dimensional strain distribution inside augmented vertebrae in the elastic regime and to failure. MethodsEight porcine vertebrae were prophylactically-augmented using two augmentation materials. They were scanned with a micro-computed tomography scanner (38.8μm voxel resolution) while undeformed, and loaded at 5%, 10%, and 15% compressions. Internal strains (axial, antero-posterior and lateral-lateral components) were computed using digital volume correlation. FindingsFor both augmentation materials, the highest strains were measured in the regions adjacent to the injected cement mass, whereas the cement-interdigitated-bone was less strained. While this was already visible in the elastic regime (5%), it was a predictor of the localization of failure, which became visible at higher degrees of compression (10% and 15%), when failure propagated across the trabecular bone. Localization of high strains and failure was consistent between specimens, but different between the cement types. InterpretationThis study indicated the potential of digital volume correlation in measuring the internal strain (elastic regime) and failure in augmented vertebrae. While the cement-interdigitated region becomes stiffer (less strained), the adjacent non-augmented trabecular bone is affected by the stress concentration induced by the cement mass. This approach can help establish better criteria to improve vertebroplasty.

Characterization of Biocompatible Materials Using Stereo Microscope 3D Digital Image Correlation

This paper presents the measurement of the sub‐micrometer deformation of biocompatible materials induced by mechanical and thermal loading with a newly developed stereoscopic microscope 3D digital image correlation (DIC) system. This technique combines a 3D DIC system based on two cameras in a stereoscopic setup with a stereoscopic microscope. This paper describes measurements of displacements in the range of 100 microns with an error of 0.1%, which is several times better than the accuracy provided by other comparable systems. The examined micro‐sized specimens are cut out of biocompatible material used for the construction of a pneumatic ventricular assist device. The results include a 3D surface profile, analysis of the sample surface deformations, and distribution of surface strains.

Virtual specimens for analyzing strain distributions in textile ceramic composites

Methods are presented for calibrating the local elastic properties of tow-scale material domains in virtual specimens of textile composites. A model of the tow geometry is calibrated using 3D tomographic data via previously published methods. The local elasticity is defined to vary with the local tow orientation and fiber volume fraction within tows. The accuracy of the tow geometry is assessed by comparing the surface geometry of virtual specimens with an alternative data source, viz. topographical data obtained by digital image correlation. Calibration of the elastic constants is validated by comparing measured surface strain distributions with computed strain distributions. An approach is also presented for extending the model to the non-linear regime, by simulating the response of virtual specimens in which the bonds between abutting tows are broken and the resulting fracture surfaces are frictionless. The latter results yield a better match to the measured strain distributions.

On the influence of fabric layer shifts on the strain distributions in a multi-layer woven composite

The influence of the relative shift between fabric layers on the local strain distributions at the mesoscopic scale of a four-layer plain weave glass fiber/epoxy matrix composite is studied through Finite Element (FE) modeling. The surface strain fields of several representative unit cells, consisting of compacted and nested plain weave layups with different layer shifts and the matrix complement, are compared to strain fields measured experimentally by digital image correlation. The layer shifts only have a small impact on the calculated homogenized macroscopic mechanical properties. However, the local strain fields are influenced significantly. Good quantitative agreement is obtained between the measured surface strain distributions and the numerical results if the layer shifts of the tested specimen are used in the FE model. The most frequently used models without layer shifts or with maximum nesting do not provide satisfactory surface strain distributions.

Mechanical assessment of a hip joint stem model made of a PEEK/carbon fibre composite under compression loading.

The aim of the work was to manufacture a composite stem model consisting of carbon fibres (CF) and polyether ether ketone (PEEK) and to perform the surface strain and stress distributions in the stem-femoral bone model under compression loading. Composite stems differing in elasticity were prepared. Three types of composite stems having different arrangements of carbon fibre reinforcements (carbon fibre roving, carbon fibre sleeves and their combinations) in the polymer matrix were made. The stems were cementless fixed in the femoral bone model channel or with the use of the polymer bone cement (PMMA). Mechanical behaviour of composite stems under compression loading was compared with a metallic stem by strain gauge measurements at different parts of stem/bone model systems. The values of stresses in the proximal part of the bone model for cemented and cementless fixations of the composite stem in the femoral bone channel were higher than those noted for the metallic stem. The increase in proximal bone stress was almost similar for both types of fixation of composite stems, i.e., cemented and cementless fixed stems. The optimal range of mechanical stiffness, strengths and work up to fracture was obtained for composite stem made of carbon fibre sleeves and carbon fibres in the form of roving. Depending on the elasticity of the composite stem model, an increase in the stress in the proximal part of femoral bone model of up to 40% was achieved in comparison with the metallic stem.

Unravelling Thiol's Role in Directing Asymmetric Growth of Au Nanorod-Au Nanoparticle Dimers.

Asymmetric nanocrystals have practical significance in nanotechnologies but present fundamental synthetic challenges. Thiol ligands have proven effective in breaking the symmetric growth of metallic nanocrystals but their exact roles in the synthesis remain elusive. Here, we synthesized an unprecedented Au nanorod-Au nanoparticle (AuNR-AuNP) dimer structure with the assistance of a thiol ligand. On the basis of our experimental observations, we unraveled for the first time that the thiol could cause an inhomogeneous distribution of surface strains on the seed crystals as well as a modulated reduction rate of metal precursors, which jointly induced the asymmetric growth of monometallic dimers.

An experimental study on the effect of joining interface condition on bearing response of single-lap, countersunk composite-aluminum bolted joints

An experimental study on the effect of joining interface condition (including shimming and interface gap) on bearing response of single-lap, countersunk composite-aluminum bolted joints are presented. The specimens consisted of a T700/3068 carbon/epoxy laminate with quasi-isotropic lay-up and an Aluminum alloy 7075T651 substrate. Bearing stress/bearing strain behavior were obtained according to ASTM standard. Both solid shim and liquid shim were considered and a comparison was made for them. 3D Digital Image Correlation was utilized to evaluate the effect of shimming on the surface strain distribution and out-of-plane deformation of the joints. One focus of the study was to investigate the effect of interface gap on the bearing performance of composite bolted joints. The interface gap was designed and characterized by variable parameters, i.e., thickness and span. It is found that compared to liquid-shim series, specimens with solid shim gain a little better bearing performance because of higher joint bending stiffness that benefits from the higher tensile modulus of solid peelable fiberglass shim. The presence of interface gap significantly weakens the bearing performance of single-lap, countersunk composite-aluminum joints by making the countersunk hole losing support from aluminum plate at the shear plane, and meanwhile intensifying the loading eccentricity of single-lap joints.

From hard to rubber-like: mechanical properties of resorcinol–formaldehyde aerogels

Four types of resorcinol–formaldehyde (RF) aerogels, stiff, brittle, low-flexible, and super-flexible are studied in this work. Despite several studies on mechanical properties on RF aerogels their response when exposed to compressive loading and their fracture behavior are not well investigated. Here, we cover aerogels with a very broad density range of 0.08–0.3 g cm−3 and compressive moduli from 0.12 to 28 MPa. We relate the microstructure of the synthesized aerogels and their behavior under uniaxial compression. Additionally, this work is the first, to our knowledge, to implement the usage of digital image correlation for characterizing the deformation of RF aerogels. The comparison of surface strain distribution of four types of aerogels provides an insight to their reaction on compressive loading.

Three Dimensional Shape and Surface Strain Distribution Measurements of the Human Face Using a Multi-View Imaging System

Three Dimensional Shape and Surface Strain Distribution Measurements of the Human Face Using a Multi-View Imaging System

An experimental study on the effect of bolt-hole clearance and bolt torque on single-lap, countersunk composite joints

An experimental study on the effect of bolt-hole clearance and bolt torque on single-lap, single-bolt, countersunk composite joints are presented. The specimens were manufactured from carbon fiber/epoxy unitapes with quasi-isotropic lay-ups. Bearing stress/bearing strain behavior, bearing strength and joint stiffness were obtained according to ASTM standard D5961. The interaction between bolt-hole clearance and bolt torque on bearing response was evaluated by varying multiple parameters. One focus was to evaluate the surface strain distribution and the out-of-plane deformation of the joints by using a commercial 3D Digital Image Correlation (DIC) system. It is found that there is interaction between bolt-hole clearance and bolt torque on joint stiffness loss and 2% offset bearing strength. Furthermore, bolt-hole clearance intensifies the surface strain concentration and the out-of-plane deformation of the joints. Bolt torque alleviates the surface strain concentration, but has little effect on the out-of-plane deformation.

130 鋼材の引張試験におけるひずみ分布の計測と最終破断までの応力-ひずみ関係

130 鋼材の引張試験におけるひずみ分布の計測と最終破断までの応力-ひずみ関係

Finite element modeling of the crushing behavior of thin-walled CFRP tubes under axial compression

A finite element modeling methodology was developed to study the crushing behavior and energy absorption characteristics of graphite/epoxy laminated circular tubes. Laminated tubes were modeled using multiple layers of shell elements with layers being tied together using tiebreak contact. A progressive damage model was used to simulate the failure within each layer while a mesh-independent energy-based failure criterion for the tiebreaks was implemented in the model to effectively simulate the delamination between layers during the crushing process. Simulation results compared very well with the experiments in terms of the load–displacement behavior, specific energy absorption, and surface strain distribution, and provided a good depiction of the failure process.

A novel stretchable micro-electrode array (SMEA) design for directional stretching of cells

Stretchable micro-electrode arrays (SMEAs) are useful tools to study the electrophysiology of living cells seeded on the devices under mechanical stimulation. For such applications, the SMEAs are used as cell culture substrates; therefore, the surface topography and mechanical properties of the devices should be minimally affected by the embedded stretchable electrical interconnects. In this paper, a novel design and micro-fabrication technology for a pneumatically actuated SMEA are presented to achieve stretchability with minimal surface area dedicated to the electrical interconnects and a well-defined surface strain distribution combined with integrated diverse micro-patterns to enable alignment and directional stretching of cells. The special mechanical design also enables the SMEA to have a prolonged electro-mechanical fatigue life time required for long-term cyclic stretching of the cell cultures (stable resistance of electrical interconnects for more than 160 thousand cycles of 20% stretching and relaxing). The proposed fabrication method is based on the state of the art micro-fabrication techniques and materials and circumvents the processing problems associated with using unconventional methods and materials to fabricate stretchable electrode arrays. The electrochemical impedance spectroscopy characterization of the SMEA shows 4.5 MΩ impedance magnitude at 1 kHz for a TiN electrode 12 um in diameter. Cell culture experiments demonstrate the robustness of the SMEAs for long-term culturing experiments and compatibility with inverted fluorescent microscopy.

Experimental investigation of the stent–artery interaction

It is well acknowledged that stent implantation causes abnormal stretch and strains on the arterial wall, which contribute to the formation and progression of restenosis. However, the experimental characterization of the strain field on the stented vessel is scant. In this work, the balloon-expandable stent implantation inside an artery analogue was captured through two high-speed CCD cameras. The surface strain maps on the stented tube were quantified with a 3-D digital image correlation technique. The strain history at one specific reference point illustrated three stenting phases, including balloon inflation, pressurization and deflation. The surface strain distributions along one axial path were obtained at various time points to demonstrate the stent–vessel interactions. The radial wall thickness reduction history was used to evaluate the pressure–diameter relationship for the balloon. Results indicated that the expansion process of the balloon was significantly altered by the external loadings from both the stent and artery analogue. In addition, the repeatability of the stenting experiments was demonstrated through two tests with a change of 5% in the stent-induced maximum first principal strain. Moreover, a computational model of the stenting procedure was developed to recapture the stenting experiments. Comparison between experiments and simulation showed a difference of 7.17% in the first principal strain averaged over the high strain area. This indicated the validation of the computational framework, which can be used to investigate the strain or stress field throughout the computational domain, a feature that is not affected by experimental techniques.

A Procedure for the Estimation of the Stress-Strain State in Reinforced Ferroconcrete Structures

We develop a procedure for the determination of the distribution of surface strains in a glue joint of a composite belt with ferroconcrete base on the use of the noncontact method of digital speckle image correlation. We also establish the level of strains in the elements of the glue joint.

Dependence of Damage-Induced Magnetization on the Plastic Deformation for X80 Steel

Metal magnetic memory (MMM) method is a novel, passive magnetic method for inspecting mechanical degradation of ferromagnetic components. In this paper, the correlation between plastic deformation and the deformation-induced magnetic field was experimentally investigated for the X80 steel. Various tensile plastic deformations are introduced into test pieces with different initial discontinuities. The surface strain distributions and normal natural magnetic fields component are measured after the tensile testings. The results show that the normal natural magnetic fields component are effective in capturing different deformation stages under tensions, the relationship between the intensity of damage-induced magnetization and the maximum plastic strain follows a simple formula proposed in this paper.

1109 回転する擬似軸表面に発生する捩りによる歪分布測定へのFBG光ファイバセンシングの適用(計測・推定・診断)

1109 回転する擬似軸表面に発生する捩りによる歪分布測定へのFBG光ファイバセンシングの適用(計測・推定・診断)

Design and Validation of a Bioreactor for Simulating the Cardiac Niche: A System Incorporating Cyclic Stretch, Electrical Stimulation, and Constant Perfusion

To simulate the cardiac niche, a bioreactor system was designed and constructed to incorporate cyclic stretch, rhythmic electrical stimulation, and constant perfusion. The homogeneity of surface strain distribution across the cell culture substrate was confirmed with ARAMIS deformation analysis. The proliferation marker, Ki-67, detected in human umbilical vein endothelial cells and 3-[4,5-dimethyl-thiazol-2-yl]-2,5-diphenyltetrazolium bromide cytotoxicity assay performed on human atrial fibroblasts confirmed biocompatibility of this novel device. Cyclic stretch treatment for 24 h resulted in the perpendicular alignment of human atrial fibroblasts. An electrical stimulation system containing carbon electrodes was characterized by electrochemical impedance spectroscopy and charge injection/recovery studies, which indicated that increased corrosive reactions were associated with a higher input voltage and prolonged pulse duration. Field stimulation delivered through this system could induce rhythmic contractions in adult rat ventricular myocytes, with contractile characteristics similar to those paced in a standard field stimulation chamber. In conclusion, this bioreactor provides a novel tool to study the interaction between physical stimulation and cardiac cell physiology.