Test Data Compression Research Articles

Parametrisation of a DEM model for railway ballast under different load cases

The prediction quality of discrete element method (DEM) models for railway ballast can be expected to depend on three points: the geometry representation of the single particles, the used contact models and the parametrisation using principal experiments. This works aims at a balanced approach, where none of the points is addressed with excessive depth. In a first step, a simple geometry representation is chosen and the simplified Hertz–Mindlin contact model is used. When experimental data of cyclic compression tests and monotonic direct shear tests are considered, the model can be parametrised to fit either one of the two tests, but not both with the same set of parameters. Similar problems can be found in literature for monotonic and cyclic triaxial tests of railway ballast. In this work, the comparison between experiment and simulation is conducted using the entire data of the test, e.g. shear force over shear path curve from the direct shear test. In addition to a visual comparison of the results also quantitative errors based on the sum of squares are defined. To improve the fit of the DEM model to both types of experiments, an extension on the Hertz–Mindlin contact law is used, which introduces additional physical effects (e.g. breakage of edges or yielding). This model introduces two extra material parameters and is successfully parametrised. Using only one set of parameters, the results of the DEM simulation are in good accordance with both experimental cyclic compression test and monotonic directs shear test.

Numerical Evaluation of Mechanical Parameters Role in GFRP Strengthened Cobblestone Masonry Walls

The use of a GFRP (Glass Fiber Reinforced Polymers) mesh, embedded as a reinforcement in a mortar coating on both wall sides, proved to be effective and reliable in increasing the masonry wall resistance and the plastic deformation capacity.In this study, a NL finite element model, developed to predict the in-plane behaviour of masonry walls strengthened by means of this technique, is refined and used in an extensive parametric study. Numerical results were compared with diagonal compression test data on URM and RM cobblestone masonry samples, showing good agreement. The masonry panel and the mortar coating were modelled as isotropic homogeneous materials with a smeared crack approach, whereas the GFRP reinforcement was modelled as a mesh of truss elements. Properties assigned to materials were derived from experimental tests.The parametric study performed before on some involved mechanical properties, considering a standard range of variation, is now extended to other parameters. Moreover, the combined variation of different properties is considered. The actual contribute of each component (masonry, GFRP mesh, mortar) on some macroscopic parameters (strength and ductility of the specimen) is evaluated.The parametric analysis highlights the important role of the GFRP mesh not only on the peak load increment but also on the post-peak behavior and, in particularly, on the ductility increment of the reinforced masonry panel. These results can address the optimization of the intervention technique and the deliverable of operative guidelines for practitioners.

Estimation of the number of specimens required for acquiring reliable rock mechanical parameters in laboratory uniaxial compression tests

The inhomogeneous variability of natural rock always leads to the uncertainty of the parameters gained from the compressive testing data of a limited number of specimens. In this technical note, a systematic comparison for two presented classical approaches, i.e. the Yamaguchi's “decision of the sample number approach (DSNA)” and the “confidence interval approach (CIA)”, is firstly made to identify the cause of discrepancy in the number of required specimens evaluated with different methods. Based on the advantages of both methods, the confidence interval dynamic process approach (CIDPA) is proposed to dynamically determine the number of required specimens during the test process. This presented technical method can effectively avoid the waste of rock specimens while ensuring the accuracy of parameters under a given confidence level. In addition, all of the methods mainly used for the uniaxial comprehensive strength with the Gaussian distribution are extended to obtain a reliable elastic modulus that usually obeys lognormal distribution. Finally, uniaxial compression tests of oblique porphyritic basalt (OP-basalt) and amygdaloidal basalt (Am-basalt) are analyzed to verify the contrast between the results obtained with different approaches and the rationality of CIDPA.

Stress-Dilatancy for Soils. Part III: Experimental Validation for the Biaxial Condition

Abstract The validation of the general stress-dilatancy relationship is shown based on biaxial compression test data presented in the literature under drained and undrained conditions. Rowe’s and Bolton’s relationships can be treated as simplified forms of the general stress-dilatancy relationship. The stress ratio values are a function of not only the dilatancy but also the intermediate principal stress, the non-coaxiality angle defined by Gutierrez and Ishihara and the stress-strain path. For many granular soils, the critical frictional state angle of the shearing resistance Φo = Φ′cv and parameters α and β are functions of the drainage condition, the stress level and the stress and strain paths.

The effect of the beta phase on the micromechanical response of dual-phase titanium alloys

This paper investigates the role of beta phase on the micro-mechanical behaviour of dual-phase titanium alloys, with particular emphasis on the phenomenon of cold dwell fatigue, which occurs in such alloys under room temperature conditions. A strain gradient crystal plasticity model is developed and calibrated against micro-pillar compression test data for a dual-phase alpha-beta specimen. The effects of key microstructural variables, such as relative beta lath orientation, on the micromechanical response of idealised alpha-beta colony microstructures are shown to be consistent with previously-published test data. A polycrystal study on the effects of the calibrated alpha-beta crystal plasticity model on the local micromechanical variables controlling cold dwell fatigue is presented. The presence of the alpha-beta phase is predicted to increase dwell fatigue resistance compared to a pure alpha phase microstructure.

Constitutive Modeling of Warm Deformation Flow Curves of an Eutectoid Steel

The capabilities of the commonly encountered Johnson-Cook and Arrhenius-type constitutive equations to describe the warm deformation flow curves of an eutectoid steel undergoing dynamic spheroidization have been compared based on the warm compression test data. Warm compression tests were conducted over the temperature range 620-770 °C and strain rates in the range of 0.01-10 s−1. The average absolute relative error values for the Johnson-Cook and Arrhenius-type constitutive equations were 44.03 and 6.50%, respectively, thereby showing that the Arrhenius-type constitutive equation is to be preferred. It is also shown that in contrast to the Arrhenius-type constitutive equation, the softening caused by dynamic spheroidization cannot be modeled using the Johnson-Cook equation.

Finite element method simulation for the prediction of mechanical properties of three-dimensional periodic bioactive glass scaffolds

The desired mechanical properties of porous tissue engineering scaffolds may differ depending on the clinical applications. Therefore, it is crucial to be able to control these properties for specific cases. In the current study, cube shape, porous, silicate-based (13-93) bioactive glass scaffolds were fabricated by robotic deposition method. Scaffolds were prepared layer by layer to form constructs with a grid-like microstructure. After binder burnout, the constructs were sintered for 1 h at 700 °C to produce scaffolds consisting of dense bioactive glass struts (∼280 ± 20 μm in diameter) at different pore widths (300 ± 50, 600 ± 25, and 900 ± 50 μm). The mechanical response of the scaffolds in compression was measured experimentally. The stress analysis of the complete scaffolds with varying pore width and layer spacing parameters has been performed by finite element method (FEM) under compression to investigate the state of stress fields created within the scaffolds. Such an analysis can be used to vary several geometrical parameters and to choose the most suitable ones for the replacement of natural tissues. The compressive strengths predicted by the FEM simulations were successfully validated by comparison with experimental uniaxial compression test data, justifying the suitability of the present approach for the optimization purposes.

Multi-laminate non-coaxial modelling of anisotropic sand behavior through damage formulation

A modified multi-laminate model, to predict non-coaxiality in anisotropic sand, is proposed in this paper. The model can easily be extended to other geo-materials only with implementing some minor provisions. To consider anisotropy of sand, two ellipsoids are utilized to summarize shear and compressive stiffness of material in different directions. Damage concept is used to take into account degradation of material through loading procedure. Ellipsoid of rigidity factors is being changed in both size and dimension, under applied strain path. Variation of ellipsoids results in change of stiffness distribution over different planes. In other words, fabric evolution in material is considered through variation of ellipsoids of rigidity factors. A simple rule is proposed for shear stress-strain relationship in loading-unloading and reloading, which captures most of the natural characteristics of sand behavior. In multi-laminate models, depending on stiffness distribution over sampling planes, stress and strain are not coaxial essentially. To achieve better results, non-coaxiality of shear stress and strain on sampling planes is considered by applying vector field concept. Shear stress in different directions of a sampling plane is considered as a vector field. This field is obtained from strain field, considering shear stiffness in various orientations. The model parameters are calibrated using uniaxial compressive test data in different directions, with respect to bedding plane on an anisotropic sand sample. To investigate capability of the model to predict non-coaxiality, results of the model are compared to experimental results obtained from pure principal stress rotation. Ultimately, good accuracy is observed in results.

Determination of confinement and plastic strain dependent post-peak strength of intact rocks

The post-peak strength behavior of rocks is important for stability analysis of underground excavations. This paper studies the confinement and plastic strain dependent post-peak strength of intact rocks. First, the post-peak behavior of rocks is studied by conducting triaxial compression tests on a coarse marble. The post-peak strengths of the rock under different confining pressures and plastic strains are obtained using the recorded stress–strain curves. A strength degradation index is then proposed to represent the post-peak strength degradation, and a negative exponential function, which includes a shape parameter n, is used to describe the relation between the strength degradation index and the confining pressure. Parameter n is plastic strain dependent, which decreases with the increase of plastic strain. The proposed strength degradation model can well capture the post-peak strength envelopes of the coarse marble under different plastic strains. Finally, two sets of triaxial compression test data from previous studies are used to further verify the strength degradation model. The peak and post-peak strength behaviors of two marbles are well represented using the proposed model. The approach proposed in this study also provides a simple yet useful method for determining the realistic residual strength of intact rocks.

A study on fracture toughness and strain rate sensitivity of severely deformed Al 6063 alloys processed by multiaxial forging and rolling at cryogenic temperature

In the present work, strain rate sensitivity, using tensile and compression test data at different strain rates, fracture toughness using three-point bend test on multi axially forged (MAF) 6063 Al alloys at liquid nitrogen temperature have been investigated. The hardness, tensile strength and strain rate sensitivity (SRS) of the deformed alloy have increased to 116 HV, 337MPa, and 0.02, from 60 HV, 220MPa and 0.004 respectively, due to accumulation of high dislocation density in the alloy processed multi axial forging at cryo temperature. Large plastic strain induced during cryo forging of 6063 Al alloy led to effective fragmentation of grains, facilitating grain refinement in the alloy. The cryoforged alloy exhibits multimodal microstructure composed of nanocrystalline, ultrafine and coarse grains. The fracture toughness of deformed (MAF and CR) 6063 Al alloy has been increased from 8.32MPam1/2 to 13.78MPam1/2 due to grain refinement and high fraction of grain boundaries. The reduction in dimple size with increasing strain showed the presence of fine grains in multiaxial forged 6063 Al as evident from fractography studies.

Stress-strain States Differences in Specimens during Triaxial Compression and Direct Shear Tests

This article compares the soil strength parameters obtained from data of triaxial compression and direct shear tests, both with dense samples of fine sand. Direct shear device and triaxial device have significant differences in stress – strain state, which is developed in the specimen during test. In order to evaluate the stress-strain state, the direct shear and triaxial tests were simulated with finite element program PLAXIS 3D.

A novel test data compression approach based on bit reversion

A novel test data compression approach based on bit reversion

Modified Block Based Technique for Efficient Test Data Compression

Test data compression is one of the major challenging tasks in VLSI. This paper targets on Test Data compression by using block based method without any variation in the system performance. Test data sets are separated into five kinds of blocks like whole zeros, whole ones, min zero/min one, max ones and complement blocks. The blocks will be read based on the presence of 0s and 1s. The analysis made in the ISCAS89 benchmark circuit shows that the proposed method is more efficient and more flexible and produces a good compression ratio when compared to the existing methods.

Temperature and data size trade-off in dictionary based test data compression

This paper proposes a new thermal-aware test data compression technique using dictionary-based coding. Large test data volume and rise in chip temperature during a test, are the two major challenges for the test engineers. Efficient filling of the don't care bits of the test patterns minimises the transition count in the scan chains, which in turn reduces the temperature of the chip to a large extent. On the other hand, high test data compression can be achieved by filling the don't-cares in a manner to get more similar sub-vectors within the test vectors. Although, both the problems rely on don't-care bit filling, most of the existing works have considered them separately. Moreover, it has been observed that, in general, thermal-aware don't-care filling leads to poor test compression, while a compression-aware don't-care filling produces high temperature. However, a high test compression with low-temperature is the most desirable expectation. In our work, we have combined the temperature reduction and the test data compression into a single problem and solved it. We have presented an integrated approach that can perform a trade-off between temperature and test compression. Experimental results on ISCAS'89, ITC'99 and IWLS'05 benchmarks show the flexibility of the proposed method to achieve a balance between temperature and test compression. The work has further been extended to reduce temperature without sacrificing compression.

Low Power Scan Chain Reordering Method with Limited Routing Congestion for Code-based Test Data Compression

Various test data compression techniques have been developed to reduce the test costs of system–on–a–chips. In this paper, a scan chain reordering algorithm for code–based test data compression techniques is proposed. Scan cells within an acceptable relocation distance are ranked to reduce the number of conflicts in all test patterns and rearranged by a positioning algorithm to minimize the routing overhead. The proposed method is demonstrated on ISCAS ’89 benchmark circuits with their physical layout by using a 180 nm CMOS process library. Significant improvements are observed in compression ratio and test power consumption with minor routing overhead.

Optimal Selective Count Compatible Runlength Encoding for SOC Test Data Compression

Test data volume amount is increased multi-fold due to the need of quality assurance of various parts of the circuit design at deep submicron level. Huge memory is required to store this enormous test data which not only increases the cost of the ATE but also the test application time. This paper presents an optimal selective count compatible run length (OSCCPRL) encoding scheme for achieving maximum compression for reduction of the test cost. OSCCPRL is a hybrid technique that amalgamates the benefits of other two techniques: 10 Coded run length (10 C) and Selective CCPRL (SCCPRL) proposed here. These techniques work on improvement of the 9 C and CCPRL techniques. In OSCCPRL, entire data is segmented in blocks and further compressed using inter block and intra block level merging techniques. SCCPRL technique is used for encoding the compatible blocks while the 10C is used to do encoding at sub block (half block length) level. In case, if no compatibility is found at block/sub block level then the unique pattern is held as such in the encoded data along with the necessary categorization bits. The decompression architecture is described and it is shown how by just the addition of few states of FSM, better test data compression can be achieved as compared to previous schemes. The simulation results performed for various ISCAS benchmarks circuits prove that the proposed OSCCPRL technique provides an average compression efficiency of around 80 %.

Optimized Test compression bandwidth management for Ultra-large-Scale System-on-Chip Architectures performing Scan Test Bandwidth Management

In today’s increasingly complex and interconnected world, system-on-a-chip (SoC) performance requirements are influenced by existing as well as evolving and emerging applications. With Moore’s law supplying billions of transistors, and uni-processor architectures delivering diminishing performance, multicore chips are emerging as the prevailing architecture in both generalpurpose and application-specific markets. As the core count increases, the need for a scalable on-chip communication fabric that can deliver high bandwidth is gaining in importance, leading to recent multicore chips interconnected with sophisticated on-chip networks. This paper introduces several test logic architectures that facilitate preemptive test scheduling for SoC circuits with embedded deterministic test-based test data compression. The same solutions allow efficient handling of physical constraints in realistic applications. A detailed experimental analysis is carried out on different provisions, architectures and test-related factors to prove the proposed method efficiency over state of methods.

Recycled Aggregate Concretes (RACs) for Structural Use: An Evaluation on Elasticity Modulus and Energy Capacities

The determination of the parameters of concrete (i.e., elasticity modulus and tensile strength) is a crucial task in material engineering. For this purpose, structural codes propose some empirical formulas to estimate the parameters of materials and are useful for designers rather than the experimental process. However, the estimated results usually vary for different standards. Hence, this research paper aims to compare the elasticity modulus formulas considering six standards (TS 500, ACI 318M-05, CSA A23.3-04, SP 52-101-2003, EN 1992-1-1 and AS-3600-2001) with experimental elasticity modulus test results. The results demonstrate that the TS 500 and EN-1992-1-1 overestimate the elasticity modulus and the SP-52-101-2003 estimates are closely aligned to the experimental results. In addition, a new equation for modulus of elasticity including the compressive strength and the density is derived for RAC. Also, energy capacities of concretes (elastic energy capacity, plastic energy capacity and toughness) are evaluated considering compressive strength test data. According to energy capacities of concretes, the proportions of 5 % silica fume (SF) and 30 % recycled aggregate (RA) are proposed as the optimum ratio.

Time and Strain-Rate Effects on Viscous Stress–Strain Behavior of Plasticine Material

AbstractA plasticine material exhibits the characterized viscous stress–strain behavior with some similarity to the behavior of clayey soils. This paper presents a series of experimental tests, which include oedometer tests, isotropic creep tests, and triaxial multistrain rate compression tests, on a plasticine material. The test study focuses on effects of time and strain rate on viscous stress–strain behavior of the plasticine material under one-dimensional (1D) straining, isotropic stressing, and triaxial compression conditions. Values of compression index (Cce), rebounding index (Cre), and creep coefficient (Cαe) are obtained from the 1D straining and 1D stressing test data. The plasticine material has no primary consolidation period, and creep occurs from the beginning. Values of Cce, Cre, and Cαe are smaller than those of the soft clays. The triaxial multistrain rate compression test data show that the stress–strain behavior of the plasticine depends on the strain rates and the confining pressures. ...

A two-step homogenization-based permeability model for deformable fractured rocks with consideration of coupled damage and friction effects

The permeability variation induced by anisotropic damage of rock blocks and nonlinear deformation of fractures is modeled with a two-step homogenization technique for deformable fractured rocks containing arbitrarily-distributed penny-shaped microcracks in rock blocks separated by multiple sets of critically orientated fractures of much large scales. The proposed model accounts for the influences of the microstructural alteration of rock blocks and fractures at the laboratory scale and the development pattern of the fracture system as well as the rock-fracture interaction at the field scale on the permeability of a fractured rock under mechanical loading or excavation condition. The proposed model was first validated by laboratory data of compression tests with permeability measurements on the Beishan granite, coupled shear-flow tests with hydraulic conductivity measurements on a granite fracture and anisotropic strength tests on the Martinsburg slate, with good agreement between the model predictions and the laboratory measurements. Numerical simulations were finally performed to examine the excavation-induced permeability change in the surrounding granitic rock of the Stripa tunnel, demonstrating the importance in considering both the damage of rock blocks and the deformation of fractures for better understanding the excavation-induced permeability change in the surrounding rock near the excavation surface.