Sulfate Attack Induced Dry–Wet Failure Modes and a Constitutive Model for Mortar Specimens with a Single Intermittent Fracture

2021 ◽  
Vol 21 (2) ◽  
pp. 04020249
Author(s):  
Tielin Han ◽  
Zhihui Li ◽  
Yunsheng Chen
Keyword(s):  
Constitutive Model ◽  
Failure Modes ◽  
Sulfate Attack

Constitutive Behavior of SAC Leadfree Alloys at High Strain Rates

2011 ◽  
Author(s):  
Pradeep Lall ◽  
Sandeep Shantaram ◽  
Mandar Kulkarni ◽  
Geeta Limaye ◽  
Jeff Suhling
Keyword(s):  
Constitutive Model ◽  
Solder Alloy ◽  
Failure Modes ◽  
High Strain ◽  
Image Correlation ◽  
Constitutive Behavior ◽  
Strain Rates ◽  
Mechanical Shock ◽  
High Strain Rates ◽  
Test Technique

Electronic products are subjected to high G-levels during mechanical shock and vibration. Failure-modes include solder-joint failures, pad cratering, chip-cracking, copper trace fracture, and underfill fillet failures. The second-level interconnects may be experience high-strain rates and accrue damage during repetitive exposure to mechanical shock. Industry migration to leadfree solders has resulted in proliferation of a wide variety of solder alloy compositions. Few of the popular tin-silver-copper alloys include Sn1Ag0.5Cu and Sn3Ag0.5Cu. The high strain rate properties of leadfree solder alloys are scarce. Typical material tests systems are not well suited for measurement of high strain rates typical of mechanical shock. Previously, high strain rates techniques such as the Split Hopkinson Pressure Bar (SHPB) can be used for strain rates of 1000 per sec. However, measurement of materials at strain rates of 1–100 per sec which are typical of mechanical shock is difficult to address. In this paper, a new test-technique developed by the authors has been presented for measurement of material constitutive behavior. The instrument enables attaining strain rates in the neighborhood of 1 to 100 per sec. High speed cameras operating at 300,000 fps have been used in conjunction with digital image correlation for the measurement of full-field strain during the test. Constancy of cross-head velocity has been demonstrated during the test from the unloaded state to the specimen failure. Solder alloy constitutive behavior has been measured for SAC105, and SAC305 solders. Constitutive model has been fit to the material data. Samples have been tested at various time under thermal aging at 25°C and 125°C. The constitutive model has been embedded into an explicit finite element framework for the purpose of life-prediction of leadfree interconnects. Test assemblies has been fabricated and tested under JEDEC JESD22-B111 specified condition for mechanical shock. Model predictions have been correlated with experimental data.

A damage constitutive model for rock mass with persistent joints considering joint shear strength

2015 ◽  
Vol 52 (8) ◽  
pp. 1136-1143 ◽  
Author(s):  
Hongyan Liu ◽  
Xiaoping Yuan
Keyword(s):  
Rock Mass ◽  
Constitutive Model ◽  
Failure Modes ◽  
Shear Failure ◽  
Jointed Rock ◽  
Joint Shear Strength ◽  
Rock Mass Strength ◽  
Damage Constitutive Model ◽  
Joint Shear ◽  
Set Up

Microcracks and joints, two types of flaws that appear in a rock mass, affect both the rock mass strength and deformability. A model that can simultaneously reflect the effect of these two types of flaws on the mechanical behavior of a rock mass with persistent joints is not yet available. This study focusses on a microcracked rock mass with persistent joints and establishes a mechanical model, accounting for the anisotropy in the rock mass strength and deformability induced by the existence of the joints. Firstly, the compound damage variable from the coupling macroscopic and mesoscopic flaws is deduced based on the Lemaitre strain equivalence hypothesis. Secondly, the corresponding damage constitutive model for a jointed rock mass is set up. Thirdly, the joint shear failure criterion is incorporated into the constitutive model to extend the model. Finally, the results of the calculation examples show that the existence of the joint will reduce the strength, enlarge the deformability, and lead to anisotropy of the rock mass. A series of calculation examples and comparisons validate that the proposed model is capable of presenting the joint-induced anisotropy in rock mass strength and deformability, determining its possible failure modes, and reasonably simulating its complete stress–strain relationship.

scholarly journals Features and Constitutive Model of Gypsum’s Uniaxial Creep Damage considering Acidization

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Wei Chen ◽  
Wen Wan ◽  
Senlin Xie ◽  
Wenlong Kuang ◽  
Wenqing Peng ◽  
...  
Keyword(s):  
Hydrochloric Acid ◽  
Constitutive Model ◽  
Stress Level ◽  
Failure Modes ◽  
Failure Time ◽  
Acid Corrosion ◽  
Creep Damage ◽  
Nonlinear Creep ◽  
Creep Tests ◽  
Acidic Groundwater

Acidic fluids cause rock erosion and further endanger the safety of rock engineering, especially the corrosion of pillars by acidic or weakly acidic groundwater. In this paper, the rock samples in the gypsum mining area were taken as the research object. Uniaxial compression creep tests were carried out under neutral water, pH=6 and pH=5 hydrochloric acid solutions, respectively. Meanwhile, the specimens before and after saturation were observed by an electron microscope scanner. The results show that (1) the gypsum specimens with pH=5 hydrochloric acid were damaged at the first stress level, while that with pH=6 and pH=7 were destroyed at the second stress level. The failure modes of the three groups were basically the same, with cleavage and end damage of different degrees. The difference is that the failure time of the former is earlier than that of the latter, which indicates that the stronger acidity causes greater corrosion on the creep of the samples. (2) From the perspective of microstructure, the samples saturated in the neutral aqueous solution and dry state are compact and complete in structure, and the whole is relatively homogeneous. However, after saturating in the acid solution, the samples significantly increased dense pores with large size and loose structure. Due to the rapid increase, the surfaces of the samples are almost like “holes”. (3) A new nonlinear creep constitutive model was established by connecting Burgers model with nonlinear viscoplastic body (NVPB) model in series, which can well describe the creep characteristics of gypsum rocks under acid corrosion.

scholarly journals FE Modeling for Bolted Wood Connection Using a Porous Constitutive Model

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Huazhang Zhou ◽  
Xiaoqiang Zhou
Keyword(s):  
Finite Element ◽  
Constitutive Model ◽  
Finite Element Modeling ◽  
Carrying Capacity ◽  
Failure Modes ◽  
Complex Stress State ◽  
Load Carrying Capacity ◽  
Confined Compression ◽  
Element Modeling ◽  
Load Carrying

According to the facts of localized crushing failure of bolt groove in wood connection with enough end distance and the three-phase composites of wood with solid (wood substance), water, and gas, a confined compression test for the wood cylinder was conducted for achieving constitutive relation under the complex stress state in wood groove. A porous constitutive model was developed according to the confined compression experiments. Then, the constitutive model was implemented in a finite element modeling of mental dowel-type fasters in wood-to-wood connections to analyse the load-carrying capacity parallel to the grain. Through changing the thicknesses of centre members and side members of wood connections made of a similar wood species, Pinus Sylvestris var. Mongolica, the effects of thickness combinations of centre members and side members on the failure modes and load-carrying capacity of bolted wood connection including numerical simulations and experiments were compared. The failure modes, including the yielding of centre member, the yielding of side member, and the yielding of the bolt, as well as the rigid rotation of the bolt, all reappeared by the finite element modeling with the porous constitutive model. The predicted deformation shapes and load-displacement relations of bolted wood connections were compared with experimental ones, and good correlations were observed. This paper presents a new approach to simulate the local embedment crushing of bolt groove in wood connections.

Multiscale Finite Element Analysis of Unbonded Flexible Risers

2014 ◽  
Author(s):  
Ben Edmans ◽  
Dinh Chi Pham ◽  
Zhiqian Zhang ◽  
Tianfu Guo ◽  
Sridhar Narayanaswamy ◽  
...  
Keyword(s):  
Finite Element ◽  
Constitutive Model ◽  
Dynamic Analysis ◽  
Large Scale ◽  
Failure Modes ◽  
Life Extension ◽  
Equivalent Material ◽  
Analysis Model ◽  
Element Analysis ◽  
Flexible Risers

Unbonded flexible risers are a key technology in existing and proposed offshore developments. With increasing water depth, the demands on risers increase and the design against hydrostatic and tension loads becomes more of a challenge. In addition, many existing subsea production systems are approaching the end of their design life and operators need to know if they can remain in-service. To enable the benefits from deepwater production and life extension projects to be realized while minimizing risks to life, property and the environment, accurate modelling and analysis tools are required to improve the prediction of failure modes and to develop a better understanding of the conditions leading to progressive failure. In this work, a multi-scale approach is adopted whereby a global dynamic analysis model is employed to determine the overall displacements of the riser and this is linked with a local model that can provide accurate forces and stresses for the prediction of collapse, fatigue damage and buckling of tensile armour wires. Firstly, we describe a nonlinear constitutive model for use in large-scale dynamic analysis of flexible risers based on an analytical homogenization of composite cylinders using the analogy between slip between pipe layers and plastic flow in continua. The model is able to reproduce the bending hysteresis behaviour observed in flexible pipes and its dependence on internal and external pressure. Secondly, we show a procedure for obtaining equivalent material parameters for this model from finite element local analyses of a flexible pipe. Finally, we show the implementation of this constitutive model in a riser system using two-dimensional co-rotational hybrid beam finite elements.

Study on Impact Compressive Behavior and Constitutive Model of BFRC

2011 ◽  
Vol 71-78 ◽  
pp. 224-228
Author(s):  
Yong Sheng Liu ◽  
Dong Gao
Keyword(s):  
Constitutive Model ◽  
High Performance ◽  
Failure Modes ◽  
Basalt Fiber ◽  
Limit Load ◽  
Fiber Reinforced Concrete ◽  
Experimental Result ◽  
Constitutive Parameter ◽  
Result Show ◽  
The Impact

Basalt fiber is a new type of high-performance fibers and it is widely studied and used in civil engineering. In this paper a super-thin basalt fiber was used and the samples of basalt fiber reinforced concrete (BFRC) were made, then the impact compressive experiments were conducted by SHPB and the factor of fiber content and loading velocity were study. The experimental result show that the super-short basalt fiber could increase the limit formation and change the failure modes of the sample, but it did not enhanced the strength of the concrete. The result also showed the limit load and deformation increase as the loading rate and it show that the BFRC have strain rate effect. Besides, based on the results of the experiments, the ZWT constitutive model being used, and the constitutive parameter were fitted.

scholarly journals An Elastoplastic Damage Constitutive Model for Cementitious Materials under Wet-Dry Cyclic Sulfate Attack

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Da Chen ◽  
Chen Du ◽  
Xingguo Feng ◽  
Feng Ouyang
Keyword(s):  
Compressive Strength ◽  
Constitutive Model ◽  
Compressive Stress ◽  
Cementitious Materials ◽  
Sulfate Attack ◽  
Ultimate Compressive Strength ◽  
Cement Mortars ◽  
Damage Constitutive Model ◽  
Number Of Cycles ◽  
Elastoplastic Damage

The mechanical properties of cement mortars subjected to wet-dry cyclic sulfate attack were studied by the compression strength test. The results showed that the ultimate compressive strength increased with number of cycles at the initial stage. However, after a certain time, it started to decrease with further increases in the number of cycles. Moreover, the concentration of the sodium sulfate solution proved to be an important factor affecting the ultimate compressive strength. Based on continuum damage mechanics theory, an elastoplastic damage constitutive model is presented to describe the mechanical behavior of cementitious materials under compressive stress. The results obtained agree well with the experimentally observed elastic, plastic, and damage characteristics of cement mortars under compressive stress.

Research on strain softening constitutive model of coal-rock combined body with damage threshold

2021 ◽  
pp. 105678952110190
Author(s):  
Tuo Wang ◽  
Zhanguo Ma
Keyword(s):  
Constitutive Model ◽  
Failure Modes ◽  
Strain Softening ◽  
Strain Curve ◽  
Model Parameters ◽  
Test Results ◽  
Underground Engineering ◽  
Rock Stratum ◽  
Damage Constitutive Model ◽  
Coal Rock

The coal seam and the roof of the roadway bear loads together in the underground engineering of coal mine. Especially for the roadway driven along the roof, its deformation is completely different from that arranged in the complete rock stratum. Accurately knowing the mechanical mechanism of coal-rock combined body can help understand the deformation and failure modes of such roadways. This article started with tests of coal-rock combined samples with different height ratios, based on the test results, a strain softening damage constitutive model of coal-rock combined body and a method for solving the parameters of the model were proposed, and the influence of the model parameters was discussed. The test results show that the stress peak value and residual strength of the coal-rock combined samples are negatively correlated with the proportion of coal in the coal-rock combined samples, and have a positive correlation with the confining pressure. The damage constitutive model fitted the test curve well. The model can accurately describe the stress-strain curve of coal-rock combined samples, and can reflect the influence of different height ratios of coal and rock samples and confining pressures. The effects of model parameters were discussed based on the damage constitutive model, which are expected to be widely used in underground engineering.

scholarly journals Research on Acoustic Emission Characteristics and Constitutive Model of Rock Damage Evolution with Different Sizes

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Haijiang Zhang ◽  
Xiaohu Zhang ◽  
Hongbo Zhou
Keyword(s):  
Acoustic Emission ◽  
Constitutive Model ◽  
Scale Effect ◽  
Damage Evolution ◽  
Failure Modes ◽  
Development Stage ◽  
Diameter Ratio ◽  
Emission Characteristics ◽  
Peak Strain ◽  
Evolution Law

In this study, considering the scale effect of rock mass, the influence of different height-to-diameter ratios on rock mechanics and acoustic emission characteristics was studied by using PFC2D software. The damage constitutive model of rock was established, and the damage evolution characteristics of rock with different height-to-diameter ratios were further analyzed. The results showed that, with the increase of height-to-diameter ratio K, the uniaxial compressive strength and peak strain of rock exhibited a gradual decrease; however, the elastic modulus gradually increased. Moreover, rock failure modes exhibited different characteristics under different K values. The scale effect showed little influence on the acoustic emission characteristics in the elastic stage; nonetheless, in the plastic deformation stage and the residual damage stage, with the increase of the rock’s height-to-diameter ratio, the maximum number of impacts of acoustic emission increased, the range of strong strain of acoustic emission decreased, and the maximum time of acoustic emission impacts increased gradually. The height-to-diameter ratio of the rock slightly influenced the zero-damage stage of the rock, but the damage affecting the rock increased slowly and accelerated the development stage. The damage evolution law was found to be similar when the K values varied from 1.0 to 2.0; however, when the K was greater than 2.0, the damage evolution law exhibited the characteristics of slowing down in the acceleration phase.

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