scholarly journals Stress-Softening in Particle-Filled Polyurethanes under Cyclic Compressive Loading

Polymers ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1588
Author(s):  
Wenshuai Xu ◽  
Mangong Zhang ◽  
Yu Liu ◽  
Hao Zhang ◽  
Meng Chen ◽  
...  
Keyword(s):  
Compressive Loading ◽  
Compressive Load ◽  
Soft Materials ◽  
Constitutive Parameter ◽  
Spherical Indentation ◽  
Mullins Effect ◽  
Stress Softening ◽  
Loading And Unloading ◽  
Load Displacement ◽  
Constitutive Parameters

Elastomer compositions containing various particulate fillers can be formulated according to the specific functions required of them. Stress softening—which is also known as the Mullins effect—occurs during high loading and unloading paths in certain supramolecular elastomer materials. Previous experiments have revealed that the load–displacement response differs according to the filler used, demonstrating an unusual model of correspondence between the constitutive materials. Using a spherical indentation method and numerical simulation, we investigated the Mullins effect on polyurethane (PU) compositions subjected to cyclic uniaxial compressive load. The PU compositions comprised rigid particulate fillers (i.e., nano-silica and carbon black). The neo-Hooke model and the Ogden–Roxburgh Mullins model were used to describe the nonlinear deformation behavior of the soft materials. Based on finite element methods and parameter optimization, the load–displacement curves of various filled PUs were analyzed and fitted, enabling constitutive parameter prediction and inverse modeling. Hence, correspondence relationships between material components and constitutive parameters were established. Such relationships are instructive for the preparation of materials with specific properties. The method described herein is a more quantitative approach to the formulation of elastomer compositions comprising particulate fillers.

A Constitutive Model for Soft Materials Incorporating Viscoelasticity and Mullins Effect

2016 ◽  
Vol 84 (2) ◽  
Author(s):  
Tongqing Lu ◽  
Jikun Wang ◽  
Ruisen Yang ◽  
T. J. Wang
Keyword(s):  
High Strength ◽  
Soft Materials ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
Mullins Effect ◽  
Butadiene Rubber ◽  
Zener Model ◽  
Rate Dependent ◽  
Effect Model ◽  
Loading And Unloading

Soft materials including elastomers and gels are widely used in applications of energy absorption, soft robotics, bioengineering, and medical instruments. For many soft materials subject to loading and unloading cycles, the stress required on reloading is often less than that on the initial loading, known as Mullins effect. Meanwhile, soft materials usually exhibit rate-dependent viscous behavior. Both effects were recently reported on a new kind of synthesized tough gel, with capability of large deformation, high strength, and extremely high toughness. In this work, we develop a coupled viscoelastic and Mullins-effect model to characterize the deformation behavior of the tough gel. We modify one of the elastic components in Zener model to be a damageable spring to incorporate the Mullins effect and model the viscous effect to behave as a Newtonian fluid. We synthesized the tough gel described in the literature (Sun et al., Nature 2012) and conducted uniaxial tensile tests and stress relaxation tests. We also investigated the two effects on three other soft materials, polyacrylate elastomer, Nitrile-Butadiene Rubber, and polyurethane. We find that our presented model is so robust that it can characterize all the four materials, with modulus ranging from a few tens of kilopascal to megapascal. The theory and experiment for all tested materials agree very well.

Determination of the Flow Stress–Strain Curves of Aluminum Alloy and Tantalum Using the Compressive Load–Displacement Curves of a Hat-Type Specimen

2019 ◽  
Vol 86 (3) ◽  
Author(s):  
Jae-Ha Lee ◽  
Hyunho Shin ◽  
Jong-Bong Kim ◽  
Ju-Young Kim ◽  
Sung-Taek Park ◽  
...  
Keyword(s):  
Aluminum Alloy ◽  
Flow Stress ◽  
Compressive Load ◽  
Type Specimen ◽  
Displacement Curve ◽  
Stress Strain ◽  
Element Analysis ◽  
Optimization Function ◽  
Load Displacement ◽  
Constitutive Parameters

The load–displacement curves of an aluminum alloy and tantalum were determined using a hat-type specimen in the compression test. Based on the results of finite element analysis, the employed geometry of the hat-type specimen was found to yield a load–displacement curve that is nearly independent of the friction between the specimen and the platen. The flow stress–strain curves of the alloy and tantalum were modeled using the Ludwik and Voce constitutive laws, respectively; furthermore, simulation of the compression event of the hat-type specimen was performed by assuming appropriate constitutive parameters. The constitutive parameters were varied via an optimization function built in matlab until the simulated load–displacement curves reasonably fit the experimental curve. The optimized constitutive parameters obtained in this way were then used to construct friction-free flow stress–strain curves of the two materials.

A Phenomenological Energy-Based Model for PBX Simulants Considering the Mullins Effect

2013 ◽  
Vol 535-536 ◽  
pp. 113-116
Author(s):  
Kee Sun Yeom ◽  
Seh Wan Jeong ◽  
Hoon Huh ◽  
Jung Su Park
Keyword(s):  
Experimental Data ◽  
Mechanical Properties ◽  
Residual Strain ◽  
Compressive Loading ◽  
Mullins Effect ◽  
Good Correspondence ◽  
Highly Nonlinear ◽  
Loading And Unloading ◽  
Nonlinear Behaviors ◽  
Test Result

PBX is known to exhibit highly nonlinear behaviors of deformation such as the Mullins effect of stress softening, hysteresis, residual strain, and frequency dependant responses. This paper proposes a phenomenological energy-based model for PBX considering the Mullins effect for isotropic, incompressible, hyperelastic, particle-filled materials. Uniaxial compressive loading and unloading tests at quasi-static states were undertaken in order to obtain the mechanical properties of the PBX simulants. The phenomenological energy-based model by Ogden-Roxburgh is, then, modified to make it consistent with the test result of PBX simulants in the case that the Mullins effect is dominant. Prediction with the new model shows a good correspondence to the experimental data demonstrating that the model properly describes the Mullins effect and the loading-unloading behavior of deformation.

Identification of Hardening Parameters of Metals From Spherical Indentation Tests

2001 ◽  
Vol 123 (3) ◽  
pp. 245-250 ◽  
Author(s):  
S. Kucharski ◽  
Z. Mro´z
Keyword(s):  
Indentation Test ◽  
Strain Curve ◽  
Load Level ◽  
Spherical Indentation ◽  
Indentation Tests ◽  
Geometric Sequence ◽  
Loading And Unloading ◽  
Plastic Hardening ◽  
Hardening Curve ◽  
Two Parameters

The identification method of hardening parameters specifying stress-strain curve is proposed by applying spherical indentation test and measuring the penetration depth during loading and unloading. The loading program is composed of a geometric sequence of loading and partial unloading steps from which the variation of permanent penetration with load level is determined. This data is used for specification of two parameters k and m occurring in the plastic hardening curve εp=σ/k1/m, where εp denotes the plastic strain.

scholarly journals Tissue Modification of the Lateral Compartment of the Tibio-Femoral Joint Following In Vivo Varus Loading in the Rat

2012 ◽  
Vol 134 (10) ◽  
Author(s):  
M. L. Roemhildt ◽  
B. D. Beynnon ◽  
M. Gardner-Morse ◽  
K. Anderson ◽  
G. J. Badger
Keyword(s):  
Articular Cartilage ◽  
Subchondral Bone ◽  
Compressive Loading ◽  
Compressive Load ◽  
Lateral Compartment ◽  
Peripheral Region ◽  
Degenerative Changes ◽  
Medial Compartment ◽  
Compressive Loads

This study describes the first application of a varus loading device (VLD) to the rat hind limb to study the role of sustained altered compressive loading and its relationship to the initiation of degenerative changes to the tibio-femoral joint. The VLD applies decreased compressive load to the lateral compartment and increased compressive load to the medial compartment of the tibio-femoral joint in a controlled manner. Mature rats were randomized into one of three groups: unoperated control, 0% (sham), or 80% body weight (BW). Devices were attached to an animal’s leg to deliver altered loads of 0% and 80% BW to the experimental knee for 12 weeks. Compartment-specific material properties of the tibial cartilage and subchondral bone were determined using indentation tests. Articular cartilage, calcified cartilage, and subchondral bone thicknesses, articular cartilage cellularity, and degeneration score were determined histologically. Joint tissues were sensitive to 12 weeks of decreased compressive loading in the lateral compartment with articular cartilage thickness decreased in the peripheral region, subchondral bone thickness increased, and cellularity of the midline region decreased in the 80% BW group as compared to the 0% BW group. The medial compartment revealed trends for diminished cellularity and aggregate modulus with increased loading. The rat-VLD model provides a new system to evaluate altered quantified levels of chronic in vivo loading without disruption of the joint capsule while maintaining full use of the knee. These results reveal a greater sensitivity of tissue parameters to decreased loading versus increased loading of 80% BW for 12 weeks in the rat. This model will allow future mechanistic studies that focus on the initiation and progression of degenerative changes with increased exposure in both magnitude and time to altered compressive loads.

scholarly journals Multi-configuration Stiffened Panels under Compressive Load: Part 1 – Theoretical Analysis

2018 ◽  
Vol 7 (3.11) ◽  
pp. 38
Author(s):  
Ramzyzan Ramly ◽  
Wahyu Kuntjoro ◽  
Amir Radzi Abdul Ghani ◽  
Rizal Effendy Mohd Nasir ◽  
Zulkifli Muhammad
Keyword(s):  
Theoretical Analysis ◽  
Experimental Analysis ◽  
Critical Loads ◽  
Input Parameter ◽  
Compressive Loading ◽  
Compressive Load ◽  
Cross Sectional ◽  
Stiffened Panels ◽  
Compression Load ◽  
Main Input

Stiffened panels are the structure used in the aircraft wing skin panels. Stiffened panels are often critical in compression load due to its thin structural configuration. This paper analyzes the critical loads of a multi configuration stiffened panels under axial compressive loading. The study comprised three main sections; theoretical analysis, numerical analysis and experimental analysis. The present paper deals only with the theoretical analysis. This first part of analysis is very important since the results will be the main input parameter for the subsequent numerical and experimental analysis. The analysis was done on the buckling properties of the panels. Four panel configurations were investigated. Results showed that even though the stiffened panels have the same cross-sectional area, their critical loads were not identical.   

Uplift behaviour of tapered piles established from model tests

2000 ◽  
Vol 37 (1) ◽  
pp. 56-74 ◽  
Author(s):  
M Hesham El Naggar ◽  
Jin Qi Wei
Keyword(s):  
Load Transfer ◽  
Compressive Loading ◽  
Compressive Load ◽  
Tensile Load ◽  
Confining Pressure ◽  
Cohesionless Soil ◽  
Uplift Capacity ◽  
Experimental Modelling ◽  
Confining Pressures ◽  
Load Tests

Tapered piles have a substantial advantage with regard to their load-carrying capacity in the downward frictional mode. The uplift performance of tapered piles, however, has not been fully understood. This paper describes the results of an experimental investigation into the characteristics of the uplift performance of tapered piles. Three instrumented steel piles with different degrees of taper were installed in cohesionless soil and subjected to compressive and tensile load tests. The soil was contained in a steel soil chamber and pressurized using an air bladder to facilitate modelling the confining pressures pertinent to larger embedment depths. The results of this study indicated that the pile axial uplift capacity increased with an increase in the confining pressure for all piles examined in this study. The ratios of uplift to compressive load for tapered piles were less than those for straight piles of the same length and average embedded diameter. The uplift capacity of tapered piles was found to be comparable to that of straight-sided wall piles at higher confining pressure values, suggesting that the performance of actual tapered piles (with greater length) would be comparable to that of straight-sided wall piles. Also, the results indicated that residual stresses developed during the compressive loading phase and their effect were more significant on the initial uplift capacity of piles, and this effect was more pronounced for tapered piles in medium-dense sand.Key words: tapered piles, uplift, axial response, load transfer, experimental modelling.

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