Deformation-based Method Research Articles

Microstructure and mechanical properties of a modified 316 austenitic stainless steel alloy manufactured by laser powder bed fusion

A 316 austenitic stainless-steel alloy, with modified alloy composition, manufactured by laser powder bed fusion (L-PBF) has been investigated. The modification of the alloy composition included addition of niobium (Nb), tungsten (W) and copper (Cu), together with a reduction in the amount of molybdenum (Mo) and an increased amount of carbon (C). To find suitable process parameters, a parameter study by varying laser power, hatch distance and scan speed was performed, centered on typical parameters used for normal 316 L. As-built material from a selected parameter configuration was then subjected to different stress relief annealing heat treatments and ageing heat treatments. The effectiveness of the stress annealing was ranked using a deformation-based method. Microstructural characterization, hardness and room temperature tensile testing were done to evaluate the effect of stress relief and aging heat treatments.It was found that a higher volumetric energy was needed to build dense material, about ∼50 % higher compared to the volumetric energy input for normal 316 L. A subsequent aging heat treatment at 725 °C for 3 h increased the strength and hardness of the material. A reinforcement of the cellular microstructure by precipitation of carbides in between the cells is believed to be the main reason for this. To completely alleviate the residual stresses it was necessary to carry out a stress relief annealing process at 950 °C, which resulted in a removal of the cellular structure and a lower strength material.

Treatment reduces the incidence of newly appearing multiple sclerosis lesions evolving into chronic active, slowly expanding lesions: A retrospective analysis.

Newly appearing lesions in multiple sclerosis (MS) may evolve into chronically active, slowly expanding lesions (SELs), leading to sustained disability progression. The aim of this study was to evaluate the incidence of newly appearing lesions developing into SELs, and their correlation to clinical evolution and treatment. A retrospective analysis of a fingolimod trial in primary progressive MS (PPMS; INFORMS, NCT00731692) was undertaken. Data were available from 324 patients with magnetic resonance imaging scans up to 3 years after screening. New lesions at year 1 were identified with convolutional neural networks, and SELs obtained through a deformation-based method. Clinical disability was assessed annually by Expanded Disability Status Scale (EDSS), Nine-Hole Peg Test, Timed 25-Foot Walk, and Paced Auditory Serial Addition Test. Linear, logistic, and mixed-effect models were used to assess the relationship between the Jacobian expansion in new lesions and SELs, disability scores, and treatment status. One hundred seventy patients had ≥1 new lesions at year 1 and had a higher lesion count at screening compared to patients with no new lesions (median = 27 vs. 22, p = 0.007). Among the new lesions (median = 2 per patient), 37% evolved into definite or possible SELs. Higher SEL volume and count were associated with EDSS worsening and confirmed disability progression. Treated patients had lower volume and count of definite SELs (β = -0.04, 95% confidence interval [CI] = -0.07 to -0.01, p = 0.015; β = -0.36, 95% CI = -0.67 to -0.06, p = 0.019, respectively). Incident chronic active lesions are common in PPMS, and fingolimod treatment can reduce their number.

Residual Deformation-Based Performance Evaluation Method for CFST Piers Subjected to Vehicle Collision

Concrete-filled steel tubular (CFST) piers have been applied in bridge structures due to their high bearing capacity, good ductility, and light weight. During their service life, CFST piers may suffer vehicle collision. Nevertheless, there is still a lack of a performance evaluation method for CFST piers subjected to vehicle impact. Therefore, this paper presents a residual deformation-based method to evaluate the performance of CFST piers under truck impact. Before that, a numerical model was developed to simulate responses of CFST piers under truck collision and validated by reported impact tests. Then, the performance levels of 6- and 12-m high CFST piers under 20 and 40 ton and 60, 100, and 140 km/h truck collisions were numerically investigated. Afterwards, a residual deformation-based performance evaluation method was proposed based on the numerical investigations. In this method, the ratio of the residual lateral deflection at the mid-height to half of the pier height was first selected as the evaluation index. Then, threshold values of the evaluation index at different performance levels were determined. Finally, an analytical model for the evaluation index was developed. Comparisons indicate that the analytical performance levels are in good agreement with the numerical results. The proposed residual deformation-based performance evaluation method can be used for design and accident analysis of CFST piers subjected to truck collision.

Component deformation-based collapse evaluation of RC frameunder different collapse criteria

Developments in performance-based earthquake engineering have emphasized the importance of evaluation of structural collapse resistance. Several collapse criteria were proposed to define structural collapse in various perspective. In this paper, collapse resistant capacity of ductile reinforced concrete (RC) frame was evaluated using different collapse criteria. Since most of the criteria focus on overall structural response, a component deformation-based method was adopted to describe the damage in component level. Incremental dynamic analysis (IDA) of a 6-story ductile RC frame conforms to current codes was conducted in OpenSEES. The collapse resistant capacity under different collapse criteria was compared. Moreover, relationship between overall structural response and the distribution of damaged components were discussed through the component deformation-based method. It was indicated that the story of maximum inter-story drift ratio is neither consistent with the one which is most seriously damaged nor with the story of maximum residual inter-story drift ratio. Furthermore, the component deformation-based method can depict structural damaged state and formation of collapse mechanism more reasonably. The analysis result evidences that structure conforms to current code have the good ductility and hardly reaches physical collapse under rare earthquake, however, the structure is more likely to be demolished due to unacceptable residual deformation.

A unified approach for austenitic and ferritic stainless steel CHS beam–columns subjected to eccentric loading

This paper develops a unified approach for assessing structural behaviour of austenitic and ferritic stainless steel circular hollow section (CHS) beam–columns​ under eccentric loading. This approach is based on combining a deformation-based method and collapse theory for stainless steel CHS beam–columns.A normalised M–N–Φ relationship of stainless steel CHS was derived based on a fibre model; the approach incorporated deformation capacity and strain hardening based on continuous strength method (CSM). The novelty of this paper is to present a closed-form solution for generating axial-load–end-moment interaction curves of the stainless steel CHS beam–column by combining the normalised M–N–Φ equation with a general beam–column equation. Besides, a critical normalised mid-height curvature was determined, which could be used to differentiate cross-section local buckling failure from global stability failure of stainless steel CHS beam–columns under combined loading. The proposed approach related the strengths of beam–columns to the effective column lengths by introducing a new non-dimensional slenderness ratio for stainless steel CHS beam–columns. It also provided an explicit way to consider the effect of column imperfections on the strengths of stainless steel CHS beam–columns. Accuracy of the derived normalised interaction curves was assessed by comparing the predictions against the test and numerical results for a wide range of non-dimensional slenderness ratios and different classes of CHS cross-sections for both stainless steel grades. A high level of accuracy and consistency was achieved in predicting the strengths of both short and long stainless steel CHS beam–columns for both types of steel grade.

Curvefusion-A Method for Combining Estimated Trajectories with Applications to SLAM and Time-Calibration.

Mapping and localization of mobile robots in an unknown environment are essential for most high-level operations like autonomous navigation or exploration. This paper presents a novel approach for combining estimated trajectories, namely curvefusion. The robot used in the experiments is equipped with a horizontally mounted 2D profiler, a constantly spinning 3D laser scanner and a GPS module. The proposed algorithm first combines trajectories from different sensors to optimize poses of the planar three degrees of freedom (DoF) trajectory, which is then fed into continuous-time simultaneous localization and mapping (SLAM) to further improve the trajectory. While state-of-the-art multi-sensor fusion methods mainly focus on probabilistic methods, our approach instead adopts a deformation-based method to optimize poses. To this end, a similarity metric for curved shapes is introduced into the robotics community to fuse the estimated trajectories. Additionally, a shape-based point correspondence estimation method is applied to the multi-sensor time calibration. Experiments show that the proposed fusion method can achieve relatively better accuracy, even if the error of the trajectory before fusion is large, which demonstrates that our method can still maintain a certain degree of accuracy in an environment where typical pose estimation methods have poor performance. In addition, the proposed time-calibration method also achieves high accuracy in estimating point correspondences.

Cold-formed steel square hollow members with circular perforations subjected to torsion

This paper describes an experimental and numerical investigation on torsional behaviour of unperforated and perforated cold-formed steel hollow section members. The material characteristics and torsional performance of YSt-310 cold-formed steel square hollow section members (conforming to Indian Standard 4923), were initially studied, experimentally. Effects of size, number, and position of circular perforation on member torsional strength were investigated using validated finite element models, via Abaqus. Additionally, using the FE analysis results, design equations were proposed in Eurocode (EN), Direct Strength Method (DSM) and Deformation Based Method (DBM) formats; for unperforated square hollow section members. The approach is then extended for perforated cases, having circular single and double perforations, using suitable reduction factors, considering effects of both cross-sectional slenderness and perforation size. The proposed design equations were assessed through reliability analysis and were found to be safe for design of cold-formed square hollow sections under torsion.

Mechanics of mouse blastocyst hatching revealed by a hydrogel-based microdeformation assay

Mammalian embryos are surrounded by an acellular shell, the zona pellucida. Hatching out of the zona is crucial for implantation and continued development of the embryo. Clinically, problems in hatching can contribute to failure in assisted reproductive intervention. Although hatching is fundamentally a mechanical process, due to limitations in methodology most studies focus on its biochemical properties. To understand the role of mechanical forces in hatching, we developed a hydrogel deformation-based method and analytical approach for measuring pressure in cyst-like tissues. Using this approach, we found that, in cultured blastocysts, pressure increased linearly, with intermittent falls. Inhibition of Na/K-ATPase led to a dosage-dependent reduction in blastocyst cavity pressure, consistent with its requirement for cavity formation. Reducing blastocyst pressure reduced the probability of hatching, highlighting the importance of mechanical forces in hatching. These measurements allowed us to infer details of microphysiology such as osmolarity, ion and water transport kinetics across the trophectoderm, and zona stiffness, allowing us to model the embryo as a thin-shell pressure vessel. We applied this technique to test whether cryopreservation, a process commonly used in assisted reproductive technology (ART), leads to alteration of the embryo and found that thawed embryos generated significantly lower pressure than fresh embryos, a previously unknown effect of cryopreservation. We show that reduced pressure is linked to delayed hatching. Our approach can be used to optimize in vitro fertilization (IVF) using precise measurement of embryo microphysiology. It is also applicable to other biological systems involving cavity formation, providing an approach for measuring forces in diverse contexts.

Structural Deformation-Based Computational Method for Static Aeroelasticity of High-Aspect-Ratio Wing Model in Pressurized Wind Tunnel

Structural Deformation-Based Computational Method for Static Aeroelasticity of High-Aspect-Ratio Wing Model in Pressurized Wind Tunnel

Prediction and classification of Alzheimer disease based on quantification of MRI deformation.

Detecting early morphological changes in the brain and making early diagnosis are important for Alzheimer’s disease (AD). High resolution magnetic resonance imaging can be used to help diagnosis and prediction of the disease. In this paper, we proposed a machine learning method to discriminate patients with AD or mild cognitive impairment (MCI) from healthy elderly and to predict the AD conversion in MCI patients by computing and analyzing the regional morphological differences of brain between groups. Distance between each pair of subjects was quantified from a symmetric diffeomorphic registration, followed by an embedding algorithm and a learning approach for classification. The proposed method obtained accuracy of 96.5% in differentiating mild AD from healthy elderly with the whole-brain gray matter or temporal lobe as region of interest (ROI), 91.74% in differentiating progressive MCI from healthy elderly and 88.99% in classifying progressive MCI versus stable MCI with amygdala or hippocampus as ROI. This deformation-based method has made full use of the pair-wise macroscopic shape difference between groups and consequently increased the power for discrimination.

Cas9 Ribonucleoprotein Delivery via Microfluidic Cell-Deformation Chip for Human T-Cell Genome Editing and Immunotherapy.

This study reports a microfluidic cell deformation-based method to deliver the Cas9 ribonucleoprotein (RNP) complexes to different cell types for efficient genome editing, including hard-to-transfect human primary CD4+ T cells. The RNP based CRISPR-Cas9 system has great advantage in shortening reaction time and reducing off-target problems, which holds great potential in future gene therapy applications.

The continuous strength method for the design of aluminium alloy structural elements

Aluminium alloys are nonlinear metallic materials with rounded stress–strain curves that are not well represented by the simplified elastic-perfectly plastic material model used in most existing design specifications. Departing from current practice, the continuous strength method (CSM) is a recently developed design approach for aluminium alloy structures, which gives consideration to strain hardening for non-slender sections. The CSM is a deformation-based method and employs a base curve to define the continuous relationship between cross-section slenderness and deformation capacity. This paper explains the background and the two key components of the CSM: (1) the base curve, which is extended herein such that the method covers both non-slender and slender sections and (2) the strain hardening material model. Three international design specifications from America, Australia/New Zealand and Europe, as well as the CSM are compared with approximately 900 aluminium alloy experimental and numerical results. Reliability analyses have been carried out to assess the reliability level of different design methods according to both the American Institute of Steel Construction (AISC) and European Standard (EN 1990) approaches. Finally, worked examples of the CSM for aluminium alloy stub columns and continuous beams are illustrated in this paper.

Longitudinal in-vivo volumetry study for porcine liver regeneration from CT data.

The use of hepatic-like cloned cord lining epithelial cells (CLEC) to enhance liver regeneration has been proposed, but has not been properly investigated in a large animal study. The paper presents a system developed for the longitudinal in-vivo volumetry study on porcine liver regeneration from computed tomography (CT) data. In this system, a rough 3D liver volume is firstly automatically segmented by a 3D mesh deformation-based method. Then a refinement step to eliminate the segmentation error is carried out by a 3D post-editing tool, followed by mesh-volume conversion and volume calculation. This system was applied in a pilot study, which was composed of 4/4 pigs in the Experimental/Control Groups, to measure liver volumes over pre- to post-operative time course. Experimental results suggest that (1) the developed system can perform CT-based porcine liver volumetry efficiently, and (2) the infusion of CLEC to liver remnant may potentially enhance the liver regeneration.

Deformation-based freeform feature reconstruction in reverse engineering

For reconstructing a freeform feature from point cloud, a deformation-based method is proposed in this paper. The freeform feature consists of a secondary surface and a blending surface. The secondary surface plays a role in substituting a local region of a given primary surface. The blending surface acts as a bridge to smoothly connect the unchanged region of the primary surface with the secondary surface. The secondary surface is generated by surface deformation subjected to line constraints, i.e., character lines and limiting lines, not designed by conventional methods. The lines are used to represent the underlying information of the freeform feature in point cloud, where the character lines depict the feature’s shape, and the limiting lines determine its location and orientation. The configuration of the character lines and the extraction of the limiting lines are discussed in detail. The blending surface is designed by the traditional modeling method, whose intrinsic parameters are recovered from point cloud through a series of steps, namely, point cloud slicing, circle fitting and regression analysis. The proposed method is used not only to effectively and efficiently reconstruct the freeform feature, but also to modify it by manipulating the line constraints. Typical examples are given to verify our method.

A Reliability Design Method of Caisson Breakwaters with Optimal Wave Heights

The paper presents an improved version of the deformation-based reliability design method by means of expected sliding distance proposed by Shimosako and Takahashi (1998 and 1999). The process of economic optimization is added, and the concept of the optimal return period for selection of design wave heights is introduced with a sample diagram for the optimal return period for three values of service lifetime. It proposes a new tolerable limit of expected sliding distance of 0.10 m instead of the value of 0.3 m adopted by Shimosako and Takahashi. The ratio of water depth to the significant wave height is demonstrated to govern the reliability design of caisson breakwaters, because of random wave breaking effects. In shallow water, a breakwater can be designed with the cross section smaller than that by the conventional design, but a larger cross section is needed in deeper water. Discussions are made on the comparison between the partial safety factor systems proposed by European groups and on the future problems to be solved for further refinements of the deformation-based design method.

Structural Damage Detection Using Localized Flexibilities

The present paper offers structural damage detection methods based on the relative changes in localized flexibility properties. The localized flexibility matrices are obtained either by applying a decomposition procedure to an experimentally determined global flexibility matrix or by processing the output signals of a vibration test in a substructure-by-substructure manner. Three methods are evaluated in the present paper: a free-free substructural flexibility method, a deformation-based flexibility method, and a strain-basis flexibility method. These methods are applied to a model ten-story building problem, an experimental bridge damage data, and a hybrid experimental-simulated engine structure. The present methods are found to correctly identify damage locations.