Influence Of Residual Stresses Research Articles

Testing Procedure for Fatigue Characterization of Steel-CFRP Hybrid Laminate Considering Material Dependent Self-Heating

Combining carbon fiber reinforced polymers (CFRP) with steel offers the potential of utilizing the desired characteristics of both materials, such as specific strength/stiffness and fatigue strength of fiber reinforced polymers (FRP) and impact resistance of metals. Since in such hybrid laminates multiple material layers are combined, a gradual failure is likely that can lead to changes in mechanical properties. A failure of the metal partner leads to an increase in stress on the FRP, which under fatigue load results in increased self-heating of the FRP. Therefore, a suitable testing procedure is required and developed in this study, to enable a reproducible characterization of the mechanical properties under fatigue load. The resulting testing procedure, containing multiple frequency tests as well as load increase and constant amplitude tests, enabled characterization of the fatigue performance while never exceeding a testing induced change in temperature of 4 K. In addition to the development of the testing procedure, an insight into the manufacturing induced residual stresses occurring in such hybrid laminates, which impacts the load-bearing capacity, was established using finite element simulation. The gathered data and knowledge represents a basis for future in-depth investigations in the area of residual stress influence on the performance of hybrid laminates and highlights its importance, since not only the used testing procedure determines the measured fatigue performance.

Influence of Equi-Biaxial Residual Stress on Spherical Indentation of Strain Hardening Materials

Residual stress plays an important role in the mechanical performance of engineering structures. In this paper, the indentation of pre-stressed strain hardening materials by a rigid sphere is simulated through the finite element method. It is shown that the mean contact pressure in the post-yield regime keeps continuously increasing with the indentation proceeding. Compared to the case without residual stress, compressive residual stress tends to increase the mean contact pressure at a given indentation depth, while tensile stress has an inverse effect. To quantitatively indicate the influence of residual stress, a nominal contact pressure is defined, which obtains its maximum value at a critical depth. The dependences of the maximum nominal pressure and the critical indentation depth on the residual stress and the material properties are determined explicitly through large numbers of simulations. Inspired by the nominal pressure deviation stemmed from residual stress, a new approach is proposed for measuring residual stress through spherical indentation tests.

Experimental and numerical investigation on ultimate strength of laser-welded stiffened plates considering welding deformation and residual stresses

The ultimate strength of laser-welded Al–Li alloy stiffened plates is experimentally and numerically analyzed in this study. The ultimate strength, failure mode, and strain evolution process of stiffened plates were measured through tension experiments combined with digital image correlation (DIC) and electrical measurements. Then, based on the established finite element model (FEM) considering material nonlinearity, geometry nonlinearity and ductile damage, the ultimate strength and failure mode of stiffened plates were simulated; and the influence of welding deformation and residual stress was investigated. The weld morphology, measured by metallographic experiment, validated the thermal–elastic–plastic model for predicting welding deformation and residual stresses. The results showed that the FEM considering welding deformation and residual stresses can accurately predict the failure modes and ultimate strength of stiffened plates.

Effects of residual stress on the stability of multi-welded integral stiffened panels

In order to clarify the influence of residual stress on the stability of 2024-T3 friction stir welded(FSWed) integral stiffened panels with multi-welds, the ANSYS software was used to establish the finite element models of two typical multi-FSWed stiffened panels. The residual stresses of two typical multi-welded stiffened panels (Panel A and Panel B) were calculated respectively using the thermal-mechanical coupling method. And the buckling and post-buckling responses of the stiffened plates were analyzed. It is shown that the residual stress distribution of stiffened panel was affected by the welding sequence. The maximum residual stress of Panel A mainly appears on the right side of the stringer, and that of Panel B appears on the stringer that is welded later. The residual stress has a great influence on the stability of the welded stiffened panels. When the residual stress profiles are taken into consideration, the critical buckling loads of welded Panel A and Panel B will decrease 14.2% and 12.4% respectively.

Effect of metal additive manufacturing residual stress on post-process machining-induced stress and distortion

This work represents the first investigation into the influence of residual stress (RS) from powder-based metal additive manufacturing (AM) on the post-process machining-induced stress and distortion for thin-walled components. Machined part distortion and surface residual stress pose major challenges in several industries, including for aerospace applications involving monolithic structures. However, the influence of initial RS in the bulk material on high-speed machining-induced stress and distortion is still not well understood. This is particularly true for more recent hybrid (additive and subtractive) manufactured components in which significant tensile and compressive RS develops from the rapid thermal cycles during the AM build. It is hypothesized in this work that, even for a simple thin-walled structure, the initial RS in the AM bulk material significantly influences the RS and distortion induced by high-speed machining. It is further hypothesized that the degree of influence of the initial RS on machining-induced RS and distortion varies significantly according to the specific tool path, even for the same net material removal. To test these hypotheses, a numerical modeling approach is presented considering a thin-walled directed energy deposition (DED) structure subjected to high-speed end-milling. A compatible RS field for the DED build is established using an iterative reconstruction algorithm based on limited neutron diffraction measurements, and the full reconstructed RS field is then imposed as an initial state in the end-milling simulation that follows. To assess the influence of the initial DED RS on the machining-induced stress and distortion, as well as to examine how this influence varies with machining strategy, two different tool paths are considered for the same net material removal, both with and without considering RS inherent to the DED build. The findings reveal significant influence of the DED RS on the high-speed machining-induced distortion and RS, and further, this influence is seen to vary greatly with the machining strategy. Normalized root-mean-square differences (NRMSD) of up to 25% and 29%, respectively, are observed in the machining-induced RS for the two different tool paths when DED inherent RS is considered. Likewise, maximum NRMSD of up to 44% and 40% are revealed in the post-machining distortion for the two respective machining strategies when DED RS is included. In addition, variations observed in the stress triaxiality computed during machining suggests that inclusion of the DED RS influences the localized response of the material near the tool-workpiece interface. The technical approach demonstrated can be extended beyond hybrid manufacturing to generate important scientific insights regarding distortion and machining-induced stress for conventionally manufactured monolithic components in the aerospace and other performance-critical industries.

Taking residual stresses into account in low-cycle fatigue design using the adjustable localisation operator method

This paper assesses the ability of the Adjustable Localisation Operator (ALO) method to predict the influence of residual stresses on the fatigue behaviour of notched components. Different initial residual stress states are introduced into notched specimens, which are then tested under cyclic loadings in a fatigue range of 103 to 105 cycles. Experimental comparisons with initially stress-free specimens have shown how tensile residual stresses reduce fatigue life under repeated compressive loading while compressive residual stresses increase fatigue life under repeated tensile loading.Finite Element Analysis (FEA) and ALO method predictions of changes in residual stress are compared to experimental measurements beforehand to assess fatigue life predictions. A modified version of Morrow’s criterion is used to account for the mean stress effect. Results have shown that the ALO method can predict the influence of residual stresses on low-cycle fatigue with the same accuracy as finite element analysis and with a significant reduction in computation time.

The influence of residual stress on the ultimate strength of longitudinally compressed stiffened panels

Welding-induced residual stress is known to reduce the ultimate compressive strength of moderately slender stiffened panels under longitudinal compression. This paper contributes a quantified measure of this strength reduction and draws some qualitative observations linking the significance of the residual stress influence to the collapse mode of the panel. A series of nonlinear finite element analyses are completed which covers a range of plate slenderness ratios (β=1.0−4.0) and column slenderness ratios (λ=0.2−1.2) typical for application to ship structures. Two residual stress scenarios are compared to a baseline stress-free condition. The first scenario includes residual stress in the plate only and the second scenario includes residual stress applied in the plate and the stiffener web. A modified edge function approach, which can be used in combination with a rule-based approach to account for the effects of residual stress, is examined with reference to the numerical results. A significant ultimate strength reduction due to residual stress is found in most test cases. It is found that residual stress in the plate causes a reduction of the ultimate compressive strength of stiffened panels regardless of failure modes. However, the residual stress in the stiffener web dominates the strength reduction of stiffened panels where collapse is triggered by beam-column buckling. Conversely it has little influence on the stiffened panels which collapse in a plate buckling mode. In addition, the modified edge function approach is demonstrated as conservative compared to the present numerical results, with its applicability confined to stocky panels.

Is 2D numerical modelling of welding process able to capture the residual notch stress intensity factor values?

Because of its local nature, the influence of residual stresses on fatigue life of welded joints in the high cycle regime can be quantified by the residual notch stress intensity factor (R-NSIF). The standard methodology used for its assessment requires a very fine mesh and this is the reason why 2D numerical models were used first in literature. The calculation of R-NSIF values via 3D models is very recent. It was found possible thanks to rapid numerical techiques such as the peak stress method. This approach was proven to work well but R-NSIF values coming from 3D models were not consistent with those obtained through 2D models. This work is aimed at solving that apparent discrepancy. 2D and 3D welding process numerical simulations applied to a carbon steel were carried out taking into account effects of metallurgical transformations and by varying the main geometrical parameters of the plates. It was found that 2D models are able to capture the R-NSIF value that is observed in the stationary residual stress distribution of the corresponding 3D models.

Reliability evaluation of ultra thin 3D-IC package under the coupling load effects of the manufacturing process and temperature cycling test

In the development of semiconductor packaging technology from planar to three-dimensional vertical integration, chip interconnection density has increased, and the distance of signal transmission has dropped to improve overall device performance. In this research, an architecture composed of through‑silicon via (TSV) and solder microbump (μbump) is utilized to assemble an ultra thin-type chip into a three-dimensional integrated circuit (3D-IC) package. To explore the influence of residual thermomechanical residual stress induced during the manufacture of the 3D-IC package on the subsequent reliability of the thermal cycling test (TCT), this study establishes a nonlinear simulation methodology for investigating the coupling effect of the manufacturing process and the TCT. The plastic and creep behaviors of the solder μbump are considered in the finite element modeling. The concerned geometric dimensions and underfill materials are also parametrically analyzed. Furthermore, the inelastic strain accumulated in the crucial SnAg solder μbump is examined. Results indicate that the residual strain in the manufacturing process causes an obvious packaging warpage and converges at the subsequent TCT stage. The creep of the solder μbump increases up to 50% in thermal cycling, thereby highlighting the importance of considering the creep model. Moreover, the parameterization of chip thickness can minimize the inelastic strain increment of the solder μbump, and the low Young's modulus of the underfill materials exerts a significant effect on the warpage of the packaging module and the stress compliance of the μbumps.

Study on the influence of localised thermal load on collapse strength of stiffened panels under longitudinal compression

The purpose of the present study is to investigate the influences of localised thermal stress on the load carrying capacity of stiffened panels under in-plane compression. The thermal loads and bending moment caused by extreme water wave seldom occur at the same time, hence, which are applied on ship structures in two load steps separately in the finite element (FE) analysis. Firstly, the stress state and structural responses of the stiffened panels under localised thermal loads with different heating zone ranges are discussed. Subsequently, the collapse behaviours of the stiffened panels under in-plane compression are simulated, in which the residual thermal stress due to the thermal loads is also included. The influences of residual thermal stress, areas of heating zone and boundary conditions on the collapse behaviours are investigated. It is found that the thermal loads could cause biaxial stress state that can reduce the load carrying capacity of the stiffened panels, which should be considered in the development of assessment formula of residual ultimate strength for ship structure design.

Fire resistance behavior of damaged steel portal frame with RBS connections

This study employs a detailed 3-D numerical modeling to investigate the fire-resistance behavior of the damaged steel portal frame with reduced beam section (RBS) connections. Ignoring the material damage parameters, and the detrimental influence of residual stresses and geometrical imperfections in the previous numerical researches has given an unrealistic response in the subsequent fire analyses. Damages were induced by the cyclic loading protocol and considering damage parameters. Then, mechanical-thermal analysis was carried out by adopting a standard fire scenario, as per ISO-834. The analysis results indicate the necessity of considering damage parameters to improve the reliability of the approach. It is revealed that fire develops thermal stresses in the bottom flange of the RBS beam. These stresses lead to severe deformation in the RBS zone, thus influencing its vital performance. Damages induced by cyclic loading drastically reduce the fire-resistance period of the frame. Once the maximum drift exceeds three times the yield limit, the steel frame is practically not capable of resisting fire. Applying extra fire load to the frame with residual lateral displacement, when the maximum lateral displacement is greater than the yield limit, the frame can only sustain the stability for less than 2 min, which will also diminish by increasing the axial column load. Through conducting a subsequent case study, it was found that the fire-resistance time of the frame is increased by decreasing the DoI of the structure at equal cyclic loadings.

Effect of Thin Polymer Layers on Mechanical Properties of Metal Surfaces

: A study of the effect of epoxy-polyester powder coatings on the mechanical properties of plates made of rolled sheet steel has been carried out. The effect of a coating with a thickness of about 100 μm on the mechanical properties of samples with a thickness of 0.7-1.5 mm was considered. Tests carried out at room and elevated temperatures showed that thin coatings insignificantly affect the mechanical properties of plates in bending and tensile tests. In particular, the stiffness of the plates under tension and bending practically does not change in the presence of coatings, despite the fact that the modulus of elasticity determined in tests of steel plates with coatings is always slightly lower than the Young's modulus of steel, due to the increased thickness of the samples, determined taking into account the presence of coatings. In contrast, in compressive strength tests, the effect of coatings is significant. In the supercritical deformation mode, the bearing capacity of the coated plates is significantly reduced, and their critical buckling load is 1.2–2.3 times lower (depending on the substrate thickness) in comparison with uncoated specimens. This effect can be explained by the influence of residual temperature stresses arising in the samples after the deposition of coatings.

Does metallurgy affect the residual notch stress intensity factor value induced by welding operations? A comprehensive study via a 3D numerical model

The residual notch stress intensity factor (R-NSIF) was found useful to quantify the influence of residual stresses on fatigue life of welded joints. Its distribution along the weld bead was recently assessed by using a 3D model. Those works focused only on the calibration of the model rather than an analysis of the R-NSIF values as a function of alloy metallurgy. This work wants to fill that gap. Both a carbon steel and an aluminum alloy were considered. Phase transformations are found to significantly influence the R-NSIF distribution with values that are more accurate compared to those obtained via previous models.

Influence of Residual Stress around Constituent Particles on Recrystallization and Grain Growth in Al-Mn-Based Alloy during Annealing.

Effect of the residual stress on the recovery and recrystallization behaviors of the cold-rolled AA3003 aluminum alloy was investigated. The evolution of deformed microstructure and dislocation density characterized by TEM and Synchrotron X-ray measurements found that the change in the ratio between low angle grain boundaries (LAGBs) and high angle grain boundaries (HAGBs) during annealing is varied depending on the initial dislocation density, where the value of HAGB/LAGBs ratio is amounted to be about 0.8 at maximum. The nucleation and growth rate of the recrystallized grains are strongly dependent on the net driving pressure associated with dislocation density increased by the amount of reduction. EBSD analysis revealed that the deformed zone composed of the fine equi-axed grains with large misorientation angles would be formed in the vicinity of the constituent particles, which is consistent with the region of the large residual stress and total displacement predicted by Eshelby inhomogeneity problem under cold rolling condition.

Influence of residual stress distribution and microstructural characteristics on fatigue failure mechanism in Ni‐based Superalloy

AbstractThe influence of residual compressive stress (RCS) depth and magnitude generated through surface treatments such as shot peening (SP), deep cold rolling (DCR), and vibro‐peening (VP) on fatigue crack mechanisms of Ni‐based superalloy is investigated. The fatigue performance with associated failure mechanisms is measured under strain‐controlled fatigue testing upto 104 cycles with total strain in the range of 0.9%–1.4% at an R ratio of 0.1 and 400°C followed by load controlled fatigue until failure. In‐depth understanding of the failure mechanism is obtained through fractography analysis, cyclic stress–strain plot, and microstructural features. A pronounced improvement in fatigue life tested at low strain range (0.9%–1.1%) is achieved after inducing RCS up to 400 μm depth. However, the fatigue life is reduced when RCS increased to 800–1000 μm depth. Failure is primarily driven by micro‐cracks formed due to balancing tensile stresses and high intensity stress concentration generated as the result of dislocation pile‐ups and slip bands. Results are discussed in detail through the evidence of grain refinement, addition of low angle grain boundaries (LAGBs), strain accumulation, and intragranular deformation in the sub‐surface.

Study of Residual Stress Compensation in Continuous Membrane Micromirrors Based on Surface Micromachining Processes

Residual stress is one of the key factors that directly determines the optical quality of micro-optical devices. With the same residual stress, the larger the aperture is, the worse the optical quality is. Therefore, continuous micromirrors are more affected by residual stress than segmented micromirrors. However, due to the complexity of boundary conditions, the influence of residual stress in segmented micromirror arrays on the device performance has been widely investigated in theory and practical applications, but only a few research results about the influence of residual stress in the continuous micromirror arrays have been reported. In this work, the residual stress both in continuous and segmented micromirror arrays is analyzed and summarized, then an accurate model for continuous micromirrors is developed. Compared with the existing models, it combines two additional factors, layer plate and point supported boundary conditions. Based on the proposed model, the change of critical stress of continuous micromirrors induced by different thicknesses of residual stress compensated membrane is theoretically investigated. Finally, the compensating experiment has been carried out, and the results show that the optical quality of micromirror can be remarkably improved, almost two orders of magnitude, with the introduction of residual stress compensation.

Modal Analysis of FSW Plate Considering the Residual Stresses Effect

In this paper, a modal analysis of the FSW plate is performed to identify the modal parameters such as: frequencies and eigenvectors. A finite element simulation is carried out by using ANSYS commercial software. The brick element called SOLID70 is used to model the weld joint in order to represent the welded structure with good precision thus determined the residual stresses in the plate. The modal analysis is use to extracting the vibration behavior of the FSW plate made of AA6061-T6 aluminum alloy with consideration the residual stresses effect on the modal parameters of the plate. The numerical results found in the friction stir welding simulation are compared by a reference plate to analyze the influence of residual stresses on the fundamental frequencies and modal deformations. The study concluded that the presence of residual stresses induced by the FSW process influences the modal behavior of the welded plates.

Thermal-mechanical-oxidation coupled first matrix cracking stress model for fiber reinforced ceramic-matrix composites

In this work, we research the combined influence of residual thermal stress, interface debonding and oxidation, and temperature on first matrix cracking stress of fiber reinforced ceramic-matrix composites (FRCMCs). Based on the shear-lag theory, the axial stress distribution of matrix and fiber considering interface oxidation and residual thermal stress is given, and we propose a criterion for interface debonding. Then, a thermal-mechanical-oxidation coupled first matrix cracking stress model is proposed for FRCMCs, according to energy balance approach. Reasonable agreement is obtained between the model predictions and available experimental results of SiCf/RBSN and SiCf/SiC composites. Moreover, the effects of some key material parameters and oxidation time on first matrix cracking stress are analyzed quantitatively by the model. This research offers a quantitative tool for evaluating and predicting the matrix cracking behavior of FRCMCs under thermal-mechanical-oxidation coupled environment.

Influences of Residual Stress, Surface Roughness and Peak-Load on Micro-Cracking: Sensitivity Analysis

This paper provides further understanding of the peak load effect on micro-crack formation and residual stress relaxation. Comprehensive numerical simulations using the finite element method are applied to simultaneously take into account the effect of the surface roughness and residual stresses on the crack formation in sandblasted S690 high-strength steel surface under peak load conditions. A ductile fracture criterion is introduced for the prediction of damage initiation and evolution. This study specifically investigates the influences of compressive peak load, effective parameters on fracture locus, surface roughness, and residual stress on damage mechanism and formed crack size. The results indicate that under peak load conditions, surface roughness has a far more important influence on micro-crack formation than residual stress. Moreover, it is shown that the effect of peak load range on damage formation and crack size is significantly higher than the influence of residual stress. It is found that the crack size develops exponentially with increasing peak load magnitudes.

The toughening of pyrochlore La2Zr2O7 by a ferroelastic NdAlO3 second phase for potential thermal barrier coating applications

AbstractThe poor fracture toughness of La2Zr2O7 severely limits its application as a high temperature thermal barrier coating topcoat material. To toughen it, a ferroelastic second phase, NdAlO3, with a Curie temperature of 1367°C has been introduced to form x NdAlO3/(1‐x) La2Zr2O7 composite ceramics by a spark plasma sintering technique, where x = 10, 20, 30, 40, and 50 mol%. The fracture toughness of sintered composite ceramic compacts is measured at both room temperature and 1200°C, respectively, by a single‐edge‐notch beam test method. The results show that, at room temperature, the residual compressive stress in the La2Zr2O7 matrix plays an important role in the toughening of composite ceramics. By eliminating this factor, the remaining toughening effects agree with the measured fracture toughness at 1200°C, suggesting that the other toughening is probably ferroelastic domain switching toughening and that it is still valid at high temperature. Furthermore, the toughening effect arising from ferroelastic domain switching is governed by the overall domain switching zone, which is determined by both individual domain switching zone width and the “concentration” of ferroelastic phases. A relatively high coercive stress of NdAlO3 and relatively low residual tensile stress in NdAlO3 second phases contribute to negligible influence of residual tensile stress on domain switching zone width, leading to the continuous increase of fracture toughness of composite ceramics with more NdAlO3 added at room temperature.