Evaluation of Soft Material Fracture Behavior via Indentation Testing With a Needle-Like Indenter

2018 ◽  
Author(s):  
Takayuki Ishino ◽  
Atsushi Sakuma
Keyword(s):  
Fracture Behavior ◽  
Soft Materials ◽  
Soft Material ◽  
Material Surface ◽  
Fracture Behaviors ◽  
Fracture Area ◽  
Material Fracture ◽  
Indentation Methods ◽  
Fracture Types ◽  
Deformation Patterns

Because the fracture behaviors of soft materials are complex, high-precision technology is needed to perform the detailed analysis necessary to produce more effective materials. Indentation methods exist to characterize the fracture behavior of soft materials, with fractures varying in accordance with the shape of the indenter. Thus, it is important to clarify the relationship between indenter shape and the fracture behaviors of soft materials, and necessary to consider the complicated deformation patterns induced by the mechanical nonlinearity of the materials. To this end, various needle-like indenter shapes are modeled via a finite element method (FEM). In this study, we employ a cone-shaped reference needle. Then, the shape is changed to have the tip form a curvilinear indentation, resembling a steep mountain ridgeline. In addition, shear strain is set as the fracture criterion for soft material in the FE analysis since the shear force resulting from penetration primarily damages the soft materials. Regarding the force applied to the needle, there is a tendency for the force to become smaller as it more resembles a cone shape. There are three fracture types: holing, opening, and slitting. Holing is generated by the cone needle, and the fracture of soft material appears along the shape of the needle. Opening fractures are generated by the needle with a curvilinearly spreading tip, forming a small slit on the surface of the soft material. Lastly, slitting fractures are also generated by the needle with a curvilinearly spreading tip, but the resulting slit is deepened without damaging the tissue surrounding the needling. These fracture types can also be classified according to the fracture area of the soft material surface, with slitting resulting in the smallest fracture area.

Contact Fracture Behaviors of Ti3SiC2 Synthesized by Hot Pressing Using TiCx and Si Powder Mixture

2005 ◽  
Vol 486-487 ◽  
pp. 217-220
Author(s):  
Sung Sic Hwang ◽  
Sang Whan Park ◽  
Seong Jai Cho ◽  
Dong Bok Lee
Keyword(s):  
Plastic Deformation ◽  
Fracture Behavior ◽  
Hertzian Contact ◽  
Coarse Grained ◽  
Vickers Indentation ◽  
Hertzian Indentation ◽  
Fine Grained ◽  
Fracture Behaviors ◽  
Hertzian Contact Stress ◽  
Contact Fracture

The contact fracture behaviors of fine-grained Ti3SiC2 and coarse-grained high purity Ti3SiC2 are examined by the Hertzian indentation and Vickers indentation technique. The Vickers hardness of bulk Ti3SiC2 is as low as 5.3~6.3 Gpa, and the Hertzian contact stress-strain curves for Ti3SiC2 deviate much from linearity, which resembles the fracture behavior of a ductile metal rather than a brittle ceramic. The contact damages by both Vickers indentation and Hertzian indentation reveal a fairly good plastic deformation nature of Ti3SiC2. Un-reacted TiCx in fine-grained Ti3SiC2 may impede the plastic deformation by slip along basal plan inside Ti3SiC2 grain, making Ti3SiC2 less plastic under loading.

Analysis for Fracture Behavior of Compactor Grinding Tooth Forging Die Based on Finite Element Method

2011 ◽  
Vol 189-193 ◽  
pp. 2491-2494
Author(s):  
Yong Shao ◽  
Ji Zhou ◽  
Ping Yi Guo
Keyword(s):  
Fracture Behavior ◽  
Local Stress ◽  
Maximum Load ◽  
Local Stress Concentration ◽  
Forging Process ◽  
Stress Changes ◽  
Fracture Behaviors ◽  
Plastic Analysis ◽  
Die Stress ◽  
Forging Die

For forging die fracture behaviors during the actual forging process of compactor grinding tooth, the fully forging process has been simulated based on FEM. Die stress changes and distributions were analyzed in details through two related simulation processes. The maximum load acting on the die which type is ideal rigid body predicted firstly. Then, the die stress can be obtained by the elastic-plastic analysis when the die bears maximum load. Results show that Local stress concentration beyond ultimate strength of material causes the fracture of lower die.

Design Methodologies for Soft-Material Robots Through Additive Manufacturing, From Prototyping to Locomotion

2015 ◽  
Author(s):  
Eliad Cohen ◽  
Vishesh Vikas ◽  
Barry Trimmer ◽  
Stephen McCarthy
Keyword(s):  
Additive Manufacturing ◽  
Modular Design ◽  
Technological Development ◽  
Deformable Body ◽  
Soft Materials ◽  
Soft Material ◽  
Hard Material ◽  
Hard Component ◽  
Contact Points ◽  
Manufacturing Techniques

Soft material robots have gained interest in recent years due to the mechanical potential of non-rigid materials and technological development in the additive manufacturing (3D printing) techniques. The incorporation of soft materials provides robots with potential for locomotion in unstructured environments due to the conformability and deformability properties of the structure. Current additive manufacturing techniques allow multimaterial printing which can be utilized to build soft bodied robots with rigid-material inclusions/features in a single process, single batch (low manufacturing volumes) thus saving on both design prototype time and need for complex tools to allow multimaterial manufacturing. However, design and manufacturing of such deformable robots needs to be analyzed and formalized using state of the art tools. This work conceptualizes methodology for motor-tendon actuated soft-bodied robots capable of locomotion. The methodology relies on additive manufacturing as both a prototyping tool and a primary manufacturing tool and is categorized into body design & development, actuation and control design. This methodology is applied to design a soft caterpillar-like biomimetic robot with soft deformable body, motor-tendon actuators which utilizes finite contact points to effect locomotion. The versatility of additive manufacturing is evident in the complex designs that are possible when implementing unique actuation techniques contained in a soft body robot (Modulus discrepancy); For the given motor-tendon actuation, the hard tendons are embedded inside the soft material body which acts as both a structure and an actuator. Furthermore, the modular design of soft/hard component coupling is only possible due to this manufacturing technique and often eliminates the need for joining and fasteners. The multi-materials are also used effectively to manipulate friction by utilizing soft/hard material frictional interaction disparity.

Tensile Fracture Characteristics of a Single Crystal Nickel-Based Superalloy

2014 ◽  
Vol 922 ◽  
pp. 819-825
Author(s):  
Dan Wu ◽  
Li Xi Tian ◽  
Chao Li Ma
Keyword(s):  
Single Crystal ◽  
Fracture Behavior ◽  
Room Temperature ◽  
Crack Nucleation ◽  
Tensile Fracture ◽  
Void Coalescence ◽  
Fracture Characteristics ◽  
Final Fracture ◽  
Nickel Based Superalloy ◽  
Fracture Area

Tensile fracture behavior of a single crystal nickel-based superalloy with different orientations and temperatures was studied. The tensile fracture surfaces and microstructure were analyzed by field emission scanning electron microscope (FE-SEM). The results showed that, generally, this single crystal nickel-based superalloy exhibited obvious tensile anisotropy. Under the condition of room temperature, the different areas of crack nucleation, propagation and final fracture area were clearly observed and varied greatly in different orientations. At elevated temperature, the fracture surface presented mixed characteristics of holes and dimples and its fracture was dominated by micro-void coalescence. Fracture mechanism was discussed.

scholarly journals Discovery of deformation mechanisms and constitutive response of soft material surrogates of biological tissue by full-field characterization and data-driven variational system identification

2020 ◽  
Author(s):  
Z. Wang ◽  
J.B. Estrada ◽  
E.M. Arruda ◽  
K. Garikipati
Keyword(s):  
System Identification ◽  
Mathematical Models ◽  
Biological Tissue ◽  
Three Dimensional ◽  
Soft Materials ◽  
Soft Material ◽  
Data Driven ◽  
Deformation Tensor ◽  
Variational System ◽  
Soft Biological Tissue

AbstractWe present a novel, fully three-dimensional approach to soft material characterization and constitutive modeling with relevance to soft biological tissue. Our approach leverages recent advances in experimental techniques and data-driven computation. The experimental component of this approach involves in situ mechanical loading in a magnetic field (using MRI), yielding the entire deformation tensor field throughout the specimen regardless of the possible irregularities in its three-dimensional shape. Characterization can therefore be accomplished with data at a reduced number of deformation states. We refer to this experimental technique as MR-u. Its combination with powerful approaches to inverse modelling, specifically methods of model inference, would open the door to insightful mechanical characterization for soft materials. In recent computational advances that answer this need, we have developed new, data-driven inverse techniques to infer the model that best explains the physics governing observed phenomena from a spectrum of admissible ones, while maintaining parsimony of representation. This approach is referred to as Variational System Identification (VSI). In this communication, we apply the MR–u approach to characterize soft biological tissue and polymers, and using VSI, we infer the physically best-suited and parsimonious mathematical models of their mechanical response. We demonstrate the performance of our methods in the face of noisy data with physical constraints that challenge the identification of mathematical models, while attaining high accuracy in the predicted response of the inferred models.

Green’s functions for soft materials containing a hard line inhomogeneity

2019 ◽  
Vol 24 (11) ◽  
pp. 3614-3631 ◽  
Author(s):  
Pengyu Pei ◽  
Guang Yang ◽  
Cun-Fa Gao
Keyword(s):  
Thermal Expansion ◽  
Heat Source ◽  
Closed Form ◽  
Hilbert Problem ◽  
Closed Form Solution ◽  
Soft Materials ◽  
Form Solution ◽  
Soft Material ◽  
Elastic Plane ◽  
Rigid Line

The linear elastic plane deformation of a soft material containing a rigid line inhomogeneity subjected to a concentrated force, a concentrated moment, and a point heat source was studied. Distinct from the existing rigid line inhomogeneity model which neglects the deformation of the inhomogeneity induced by both the mechanical stresses and thermal expansion, the current model allows for the thermal expansion-induced stretch and rotation of the inhomogeneity. In this context, we derive the closed-form solution for the full stress field in the soft material by solving the corresponding Riemann–Hilbert problem. In particular, our solution can serve as the Green’s function to establish other analytical solutions for more practical and complicated problems in this area. Several numerical examples are presented to illustrate our closed-form solution corresponding to the thermal loading. It is found that the presence of the heat source contributes significantly to the rigid rotation of inhomogeneity, and the thermal expansion-induced stretch of the inhomogeneity has a great impact on the stress intensity factors at the inhomogeneity tips.

scholarly journals Measurement of Shear Strain Field in a Soft Material Using a Sensor System Consisting of Distributed Piezoelectric Polymer Film

Sensors ◽  
2020 ◽  
Vol 20 (12) ◽  
pp. 3484 ◽  
Author(s):  
Fengyu Li ◽  
Yasuhiro Akiyama ◽  
Xianglong Wan ◽  
Shogo Okamoto ◽  
Yoji Yamada
Keyword(s):  
Shear Strain ◽  
Strain Field ◽  
Polyvinylidene Fluoride ◽  
Three Dimensional ◽  
Soft Materials ◽  
Soft Material ◽  
Sensor System ◽  
Skin Damage ◽  
Skin Contact ◽  
Sensing Model

Measurement of the internal stress and strain distributions within soft materials is necessary in the field of skin contact safety. However, conventional interactive force sensors cannot efficiently obtain or estimate these distributions. Herein, a shear strain sensor system consisting of distributed built-in piezoelectric polyvinylidene fluoride (PVDF) polymer films was developed to measure the internal shear strain field of a soft material. A shear strain sensing model was mathematically established, based on the piezoelectricity and mechanical behavior of a bending cantilever beam, to explain the sensing principle. An experiment in three-dimensional measurement of the shear strain distribution within an artificial skin was designed and conducted to assess the sensitivity of the sensing model. This sensor system could visualize the shear strain field and was sensitive to different contact conditions. The measurement results agreed well with the results of numerical simulation of the substrate, based on contact mechanics. The proposed sensor system was confirmed to provide a new sensing method for the field of shape analysis. The sensor system can be applied to develop sufficiently sensitive electronic skin and can significantly contribute to skin damage analysis and skin contact safety assessment.

Nanomechanical Effects

2021 ◽  
pp. 253-272
Author(s):  
C. Julian Chen
Keyword(s):  
Barrier Height ◽  
Contact Area ◽  
Soft Materials ◽  
Sample Surface ◽  
Soft Material ◽  
Measurable Effect ◽  
Tunneling Barrier ◽  
Hard Materials ◽  
Small Force ◽  
The Stability

This chapter discusses the effect of force and deformation of the tip apex and the sample surface in the operation and imaging mechanism of STM and AFM. Because the contact area is of atomic dimension, a very small force and deformation would generate a large measurable effect. Three effects are discussed. First is the stability of the STM junction, which depends on the rigidity of the material. For soft materials, hysterisis is more likely. For rigid materials, the approaching and retraction cycles are continuous and reproducible. Second is the effect of force and deformation to the STM imaging mechanism. For soft material such as graphite, force and deformation can amplify the observed corrugation. For hard materials as most metals, force and deformation can decrease the observed corrugation. Finally, the effect of force and deformation on tunneling barrier height measurements is discussed.

Generalized Method to Analyze Acoustomechanical Stability of Soft Materials

2016 ◽  
Vol 83 (7) ◽  
Author(s):  
Fengxian Xin ◽  
Tianjian Lu
Keyword(s):  
Wave Propagation ◽  
Acoustic Waves ◽  
Acoustic Radiation ◽  
Radiation Force ◽  
Soft Materials ◽  
Theoretical Method ◽  
Positive Definite ◽  
Soft Material ◽  
Acoustic Radiation Force ◽  
Tangential Stiffness

Acoustic radiation force generated by two counterpropagating acoustic waves in a thin layer of soft material can induce large deformation, and hence can be applied to design acoustomechanical actuators. Owing to the sensitivity of wave propagation to material geometry, the change of layer thickness may enhance wave propagation and acoustic radiation force, causing a jumping larger deformation, i.e., snap-through instability. Built upon the basis of strong elliptic condition, we develop a generalized theoretical method to evaluate the acoustomechanical stability of soft material actuators. We demonstrate that acoustomechanical instability occurs when the true tangential stiffness matrix ceases to be positive definite. Our results show that prestresses can not only enhance significantly the acoustomechanical stability of the soft material layer but also amplify its actuation stretch in thickness direction.

scholarly journals COMPARISON OF FRACTURE BEHAVIOR OF SHARP WITH BLUNT CRACK TIP IN NANOCRYSTALLINE MATERIALS BY MOLECULAR DYNAMICS SIMULATION

2012 ◽  
Vol 05 ◽  
pp. 410-417 ◽  
Author(s):  
MOVAFFAQ KATEB ◽  
KAMRAN DEHGHANI
Keyword(s):  
Molecular Dynamics ◽  
Nanocrystalline Materials ◽  
Fracture Behavior ◽  
Md Simulation ◽  
Crack Tip ◽  
Dislocation Nucleation ◽  
Dynamics Simulation ◽  
Blunt Crack ◽  
Pile Up ◽  
Fracture Behaviors

Molecular Dynamics (MD) simulation was used to figure out the fracture behaviors of nanocrystalline materials (NCM). The simulation was based on more than 13 thousand atoms considered for two systems with sharp and blunt crack tip in NCM. Their atomic level resolution provides novel insights into the fracture behavior of NCM. The results show semi brittle manner for both sharp and blunt tips. Dislocation nucleation and pile up at grain boundary (GB), lead to forming voids at GB. Merging mechanism of voids ahead of crack tip causes crack growth.

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