It is challenging to find lightweight blast mitigating structures for protecting civilian and military infrastructure. Here we synthesize a surrogate optimization algorithm with a numerical technique ...to analyze dynamic deformations of sandwich structures with fiber-reinforced face sheets perfectly bonded to eight PVC foam layers, and to simultaneously minimize the structural mass and maximize its blast mitigating capabilities. The eighteen variables to be optimized are thicknesses of the two face sheets and of the eight foam layers and the lay-up of the core layers such that either the total reaction force transmitted to a rigid substrate or the deflection of the back face is minimized. The deformations of the structure and the pressure produced by detonating a charge are simulated using the commercial finite element software ABAQUS. The progressive damage and delamination between adjacent layers of the face sheets and their debonding from the core are, respectively, considered using a user-defined subroutine and a cohesive zone model. It is found that for an optimum structure, the mass density and the elastic modulus of the core layers does not continuously vary through the thickness, i.e., the core is not comprised of a functionally graded foam. The low (high) density foam layers minimize the total reaction force (the back face deflection).
•Optimization of sandwich structures for blast mitigation and minimum mass.•Damage initiation and propagation due to Hashin’s failure criteria for 3-D deformations.•The foam core not functionally layered for optimum geometries.•Computed maximum strain rate in a foam is about 1200/s.
Relation between the Mogi and the Coulomb failure criteria Al-Ajmi, Adel M.; Zimmerman, Robert W.
International journal of rock mechanics and mining sciences (Oxford, England : 1997),
04/2005, Letnik:
42, Številka:
3
Journal Article
Recenzirano
We have shown that linear Mogi criterion does a good job in representing rock failureunder polyaxial stress states. When σ 2 = σ 3 the linear version of Mogi's triaxial failurecriterion reduces ...exactly to the Coulomb criterion. Hence, the linear Mogi criterion can be thought of as a natural extension of the Coulomb criterion into three dimensions (i.e., polyaxial stress space). As Mohr's extension of the Coulomb criterion into three dimensions is often referred to as the Mohr-Coulomb criterion, we propose that the linear version of the Mogi criterion be known as the "Mogi-Coulomb" failure criterion. The classical Coulomb failure criterion can therefore be thought of as a special case, which applies only when σ 2 = σ 3 of the more general linear Mogi failure criterion. Furthermore, we found that the numerical values of the parameters that appear in the Mogi-Coulombcriterion can be estimated from conventional triaxial test data. Thus, this polyaxial failurecriterion can be applied even in the absence of polyaxial (true triaxial) data. This offers a great advantage, as most laboratories are equipped to conduct only traditional σ 2 = σ 3 tests. Finally, we showed that if the linear form of the Mogi criterion is used, the parameters that appear in it can be unambiguously related to the traditional parameters appearing in the Coulomb failure law. The lack of such a relationship for the parameters appearing in the power-law Mogi criterion has been cited in 8 as a major drawback to the use of that model.
Pressurized hybrid composite pipe structures, produced by filament wound subjected to impact loads, were numerically investigated. A combined 3D-FE Model based on the use of interlaminar and ...intralaminar damage models is established. Intralaminar damages such as matrix cracking and fibre failures are predicted using 3D Hashin criteria, whereas interlaminar damage (delamination) was evaluated using cohesive zone elements. The damage model was coded and implemented as a user-defined material subroutine (VUMAT) for Abaqus/Explicit. Numerical results in the form of contact force, displacement and energy dissipated compare well with the experimental results. Predicted matrix damage in each cross-ply of hybrid composite pipe and delamination onset were also presented in this paper. The ability of this new 3D model to simulate the damage evolution in the full-scale pressurized hybrid composite pipe under low-velocity impact events were demonstrated throughout comparison with existing experimental results published.
This study aims to evaluate the applicability of failure criteria and damage evolution methods in the finite element analysis of composite laminates under low-velocity impact. Implemented by the ...user-defined VUMAT subroutine in ABAQUS, various progressive damage models are used to predict damage initiation and accumulation in a T700GC/M21 composite laminate. Cohesive elements are inserted between adjacent plies to capture interface delamination. The applicability of damage models is investigated by comparing the global mechanical response and distribution of various damage modes. A new variable, equivalent damage volume, is introduced to quantitatively describe the predicted damage when using different models. The numerical results establish that Hashin and Puck failure criteria generate matrix compression damage in more layers of the composite. Maximum stress and Tsai–Wu criteria are not preferred due to their improper predictions in terms of damage area and permanent deformation of the laminate. As for damage evolution laws, the equivalent strain method provides faster stiffness degradation of the laminate and a smaller area of matrix damage compared with the predictions of the equivalent displacement method.
This paper presents the low-velocity impact behavior of sandwich panel with carbon fiber reinforced plastic (CFRP) composite facesheet and Nomex honeycomb core through experimental and numerical ...methods. Experiments were carried out on two thickness of honeycomb core at various impact energy levels. The dynamic response including contact force history and energy absorption as well as contact duration was recorded. The damage modes were obtained through non-destruction inspection (NDI) C-scan and microscopic observation. A refined three-dimensional finite element model combined with continuum damage mechanics (CDM) was developed with composite plies and detailed honeycomb core. Physically-based Puck’s composite failure criteria and energy based progressive damage model were used to capture the intralaminar damage initiation and evolution, respectively. The interlaminar damage of facesheet and debonding of facesheet/core interface were predicted using cohesive element. The hexagonal honeycomb cells were characterized in FE model with an elasto-plastic constitutive model and damage criterion in detail during impact. The simulation results show good agreements with experiments and the model can be used to predict the low-velocity impact response and impact damage effectively. More detailed responses, such as internal damage details, damage modes and evolution, are observed and discussed with the numerical model proposed.
In this paper, a 3D finite element model is established in ABAQUS/Explicit based on a modified progressive damage model to study the dynamic mechanical response and damage development in cross-ply ...composite laminates subjected to low-velocity impact. The 3D Hashin criterion and the damage evolution model with the through-thickness normal stress component σ33 are applied to predict the intra-laminar damage initiation and evolution. The cohesive elements with the bilinear traction-separation relationship are inserted between layers to predict the inter-laminar delamination induced by impact loading. A user-material subroutine VUMAT involving the modified progressive damage del of intra-laminar and inter-laminar damage is coded and implemented in the finite element package ABAQUS/Explicit. The numerical results of three different impact energies (7.35, 11.03 and 14.70 J) are analyzed by the impact force–time, force-displacement and energy-time histories curves as well as different damage modes. The respectable relationship between numerical simulation and experimental result indicates that the proposed modified method is more suitable for low-velocity impact on composite laminates under different impact energies than the previous method without σ33. Moreover, the effects of Smt and Smc on global mechanical response and local damage predictions for laminates are discussed in detail. It can be concluded that both of the coefficients should be adopted between 0.93 and 0.96 when using this damage model to simulate composite laminates under low-velocity impact.
Carbon fiber-reinforced polymer (CFRP) tendons possess significant potential for applications in civil engineering, owing to their exceptional mechanical properties. Achieving effective anchoring of ...CFRP tendons is a crucial factor in promoting their engineering applications. In this paper, a novel mechanical integrated wedge-type anchorage system consisting of two components, a single-channel integrated sleeve-wedge and a steel barrel, has been proposed to achieve the anchorage of CFRP tendons. The internal stress distribution and anchoring performance of the proposed anchorage system were analyzed using the finite element (FE) method. Furthermore, this paper focused on the transverse damage of CFRP tendons caused by the wedges, proposing a design method based on transverse damage control. The effects of the slope angle of the integrated sleeve-wedge, the presetting force, anchorage length, and the differential angle on the slip behavior of the anchorage system and the degree of transverse damage to CFRP tendons were investigated. Ultimately, the anchoring performance of the optimal design was experimentally validated. The results show that the design of the proposed anchorage system necessitates careful consideration of damage to CFRP tendons induced by stress concentration around wedge slits. The matrix failure index FIFT of the LaRC05 failure criteria proves effective in evaluating transverse damage under complex stress conditions. The average tensile strength of the anchorage system for the 5 mm CFRP tendons was 2565 MPa, exceeding the guaranteed tensile strength value of 2513 MPa. The anchorage system successfully achieved the desired explosive failure mode for CFRP tendons. This attests to the feasibility of the design concept of the proposed anchorage system and underscores the necessity of incorporating transverse damage control in the design approach.
•A novel mechanical integrated wedge-type anchorage system (NMIWTAS) for CFRP tendons was designed.•The design concept of NMIWTAS was validated through finite element (FE) method and anchorage test.•The matrix failure index of Larc05 failure criteria can be used to evaluate the damage degree of CFRP tendons.•The NMIWTAS based on the damage control method can achieve the anchor efficiency of 102 %.
Due to a filament-by-filament and layer-by-layer structure produced by an additive manufacturing (or namely 3D printing) technique, mechanical properties of 3D printed materials diverge considerably ...from those of carbon fiber reinforced polymer (CFRP) composites made by traditional processes. This study aims to experimentally characterize their mechanical properties through the off-axis tensile, compressive and V-notch shear tests. Advanced imaging techniques, such as digital image correlation (DIC), scanning electron microscopy (SEM) and computed tomography (CT), are used to investigate anisotropic nature of materials and failure mechanisms of the 3D printed CFRP composites. The applicability of conventional failure criteria to the 3D printed CFRP composites, including Tsai-Wu, Tsai-Hill, Hoffman, Maximum Stress, Hashin, Puck and LaRC05, is assessed systematically. The experimental results divulge that the filament-by-filament and layer-by-layer features intrinsic to 3D printed CFRP composites lead to an uneven yet organized distribution of voids. This characteristic contributes on the development of claw mark strain patterns, parallel track inter-fiber failure patterns, and distinct compression failure modes such as delamination and interlayer crack under loading perpendicular to the fiber direction. The voids in the 3D printed CFRP materials are partially responsible for the significant asymmetry when off-axis angle increases. Notably, the conventional failure criteria exhibit limited capability for predicting the off-axis tensile strength accurately. This phenomenon can be attributed to the redistribution of inherent fiber waviness as the fiber encounters tensile loads. Based on the experimental results, the inter-fiber failure as per the LaRC05 is modified to obtain an enhanced failure criterion for predicting the off-axis tensile strength. This study is expected to provide fundamental understanding of structural characteristics and mechanical properties for 3D printed CFRP composites.
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•Asymmetric elasticity and multiscale failure behaviour of 3D printed C-CFRP.•The voids contributes to the distinctive deformation and failure modes.•The conventional failure criteria can't predict the off-axis tensile strength accurately.•A refined LaRC05 failure criteria considering the redistribution of fiber waviness.
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