Levels Of Work Hardening Research Articles

Research on the bonding performance and mechanism of hot-rolled Ti/steel clad plates based on surface state

The interfacial bonding strength of Ti/steel clad plates is a crucial factor that affects their application. However, the effect of the surface state, which is a significant determinant, is often neglected. In this study, various surface treatment processes were employed to create different surface states based on the hot-rolling of double-layer steel billets, and the effects and mechanisms of these surface states on the bonding performance of hot-rolled Ti/steel clad plates were systematically examined. The results showed that the Ti/steel clad plates pretreated with a louver wheel exhibited the highest bonding performance, with the average bonding strength peaking at 328.67 MPa and stabilising at approximately 300 MPa. This strength was approximately 50 % greater than that achieved with wire brush treatment and significantly surpassed the results obtained with sanding belts and diamond grinding discs. The analysis of the surface properties and microstructural characteristics revealed that various surface treatments led to different levels of work hardening and lattice distortion at the surface, and the interface bonding strength depended on the degree of matching between these factors. Proper surface hardening can promote the transformation of lattice distortion energy into a diffusion-driving force of elements on both sides of the interface during rolling, enabling sufficient diffusion of elements on both sides of the interface and obtaining good interface bonding performance. A phenomenological prediction mechanism-based model was established to quantify the relationship between the surface state and the bonding strength. This study elucidats the mechanism by which the surface state of materials influences the interfacial bonding performance of hot-rolled Ti/steel clad plates. These findings have significant implications for enhancing the interfacial properties of these composite plates and for selecting suitable pre-rolling surface treatment processes.

Shear texture development and microstructural analysis of friction stir welded AA5754 sheets during forming at different strain paths

Modern automotive, marine, and aviation industries seek defect-free Al-Mg alloy welds for uniform strain distribution during complex shaping. Despite this critical need, limited research was done on the formability of friction stir welded blanks. This study aimed to examine the shear texture development and microstructural analysis of friction stir welded AA5754 sheets during forming at different strain paths. It is also sought to correlate the changes ensued before and after deformation with microstructures and formability. Four combinations of rotational speeds (1200 and 1600 rpm) and traverse speeds (90 and 150 mm/min) were used to produce 1.5 mm thick butt-welded AA5754 sheets. Limit Dome Height (LDH) experiments were performed for three different strain paths (uniaxial, plane, and biaxial) to assess the formability in terms of strain path diagram. Strain path curves and von Mises effective strains revealed that plane strain limits were lowest for most parameter combinations, except 1200 rpm - 150 mm/min and a peculiar behavior was observed in the minor strains of biaxial strain paths. The reason for this peculiar behavior was further confirmed by weak or absent texture C in biaxial strain paths and declining pole figure intensities at 1200 rpm - 150 mm/min across the strain paths during shear texture analysis. Grain orientation spread (GOS) maps differentiated deformed and recrystallized regions. The minimum average Taylor factor (M) in the biaxial strain path of deformed base material indicated maximum slip system activation. Moreover, for all the specimens the average M ranged between 3 and 4, which signified that the grains exhibited adequate amount of stress levels and high level of work hardening.

Influence of deformation substructure on the strain compatibility of ferrite and bainite in a commercial pipeline steel

The strain instability due to hardening of the soft phase is a key factor in premature failure of pipeline steels after work hardening. In this work, we reveal the hardening mechanism of ferrite is actually the strengthening effect of deformation substructures on the flow stress, where the strengthening contribution by the low angle grain boundaries (LAGBs) is the main stress enhancement way. It is able to subdivide the ferrite into many sub-grain structures through dynamic evolution between geometrically necessary dislocations (GNDs), LAGBs and high angle grain boundaries (HAGBs) during work hardening. These subgrains have independent orientations and can be further subdivided, thus causing the Hall-Petch strengthening effect. Based on the hardening mechanism of ferrite, the representative volume element model with different levels of work hardening is developed. As the level of work hardening increases, the strain compatibility is gradually reduced between ferrite and bainite. The strain localization factor is increased from 0.023 to 0.061, the plastic deformation difference between the two phases is increased from 6.71% to 10.93%, and strain partitioning coefficient is reduced from 7.11 to 3.07. This work will contribute to better understand the substructure strengthening of dual-phase materials and provide a new idea for the protection of work-hardened metals.

Cryogenic die-less spinning of aluminum alloy thin-walled curved components and microstructure evolution

Cryogenic die-less spinning was proposed to address wrinkling and cracking, which occur in traditional spinning, to form large thin-walled curved components. A finite element model for this technique was developed, and die-less spinning at room temperature (RT) and cryogenic temperature (CT) was conducted to determine its feasibility. The wall thickness and the hardness of the components were then measured, and the microstructure evolution was observed to evaluate the forming accuracy and quality of the components. The component could be formed entirely (with a height of 45 mm) at cryogenic temperature feeding in a single pass, but the component formed at room temperature was broken with a height of 17.2 mm. In addition, the component formed via a single-pass feed path had a large stress concentration area and poor wall thickness accuracy. Results indicate that cryogenic temperature and multi-pass feed path could improve the formability of the component. Owing to the suppression of dynamic recovery at cryogenic temperature, smaller substructures were formed, and more dislocations accumulated in the grain, causing a higher level of work hardening of the alloy. The dislocation density of the components formed via a single-pass feed path at CT, multi-pass feed path at CT, and multi-pass feed path at RT were 3.40 × 1013, 2.62 × 1013, and 1.97 × 1013, respectively. The plasticity of the alloy was significantly improved at cryogenic temperatures because of the increased critical dislocation density and the improved work hardening ability.

Instrumented indentation for determining stress and strain levels of pre-strained DC01 sheets

In classical mechanical testing, determining the stress and strain states of complex shape specimens turns out to be very challenging, especially in the most deformed regions. In the latter case, when not enough material is present, non-destructive testing is needed for determining the corresponding mechanical state. In this study, a novel approach, based on the local quasi-non-destructive instrumented indentation technique (IIT) coupled with the inverse analysis technique (IAT), is used to determine the stress and strain levels of pre-strained DC01 specimens using monotonic and non-monotonic loading paths. Monotonic and cyclic shear tests as well as Marciniak tests, in both plane and equi-biaxial strain states, are used to apply different pre-strain levels. For monotonic loading paths, i.e. monotonic shearing and Marcianiak tests, the applied methodology showed very satisfying results in determining the stress and strain states of the pre-strained specimens, especially for pre-strain values close to the representative indentation strain values. A maximum stress error of less than 15% was obtained in the case of the highest applied pre-strain value (29.04%). The purely isotropic Voce hardening law was adopted for determining the hardening behavior of the studied specimens in both cases: as-received and pre-strained. In the case of cyclic shear, a mixed isotropic-kinematic hardening law is to be used to determine the stress and strain states of the pre-strained specimens. Adopting a mixed isotropic-kinematic Chaboche hardening law led to satisfying results where the estimation errors of the applied pre-strain value and corresponding yield stress didn't exceed 6% and 1.3%, respectively. The obtained results show that the proposed indentation-based method can be very useful in estimating the work-hardening level and corresponding plastic deformation of pre-strained parts under various loading paths

Оценка уровня упрочнения стружки из алюминиевого сплава, предназначенной для последующей обработки давлением

Introduction. It is noted that the chip is an undesirable type of metal scrap, because it has a developed surface, which creates conditions for more intense interaction with the surrounding atmosphere. This creates conditions for oxidation and gas saturation, especially at elevated temperatures typical of remelting processes. Therefore, the process of chip utilizing is considered, bypassing the remelting stage. The aim of the work is to establish the level of work hardening of chips during the processing of aluminum alloys and to predict its effect on the subsequent processing process. Research methods: to assess the deformed state, the finite element method was applied, implemented in the RAPID-2D software package. The sequence of actions included the creation of the initial shape of the deformation region and the configuration of the tool. The mutual displacement of the tool and the deformable material is specified using the corresponding boundary conditions. The deformable medium is a viscous-plastic material with power-law hardening, the physical and mechanical properties correspond to an aluminum-magnesium alloy. Results and discussion: the solution obtained shows that the degree of shear deformation in the chips can reach a value of more than 2. In this case, a higher level of deformation is localized on the side of the convex part of the chip. The comparison of the solution with those obtained earlier by other authors is carried out and its similarity is shown. In the considered solution, the difference in the degree of work-hardening of the chips along its thickness is 36 %. A variant of the sequence of processing the workpiece first by cold deformation, and then by cutting is considered. The field of application of the results of the work is the development of methods for the processing of technogenic formations. Conclusions. During the cutting process, the plastic deformation of the chips reaches significant values. In this paper, the difference in the degree of shear deformation in the chip thickness is established, depending on the proximity of the cut layer to the surface of the cutting tool. It is proposed to take this difference into account at the subsequent stages of chip processing. The presence of the marked inhomogeneity of mechanical properties leads to consequences in the form of an inhomogeneous distribution of the temperature of the beginning of recrystallization during subsequent operations of heat treatment or hot deformation treatment. The principle of additivity of the degree of deformation obtained by the metal at the stage of plastic shaping of the workpiece and the shaping of the chip itself is introduced.

Effects of the cooling mode on the integrity and the multi-pass micro-scratching wear resistance of Hardox 500 ground surfaces

In this paper, effects of the cooling mode used in grinding of Hardox 500 on the material grindability, ground surface integrity, and multi-pass micro-scratching wear resistance are investigated. Three modes are experimented: dry grinding, soluble oil, and cryogenic cooling modes. Results showed that the cryogenic cooling achieved high levels of work hardening and compressive residual stresses. Moreover, it was found that the cryogenic cooling improves the multi-pass micro-scratching wear resistance of Hardox 500 comparatively with the polished state and ground surfaces under dry or soluble oil conditions. The improvement rates of the wear volumes generated by the cryogenic cooling represent 46% and 63% of the volumes generated for the polished state when scratch load of 10 N and 20 N were applied respectively. These improvements are discussed based on the integrities of the scratched surfaces and sub-surfaces.

On the investigation of reuse potential of SnPb-solder affected copper subjected to work-hardening and thermal ageing

The reuse potential of SnPb-solder affected old/waste copper is investigated under the influence of work hardening and thermal treatments. In fact, the urge of using old copper to manufacture new components necessitates useful characterization of various properties to explore its reuse potential. In this context, a number of physico-mechanical properties of interest, namely, hardness, conductivity, thermal stability, structure, etc. are chosen here to characterize the solder-affected copper materials as well as analyze their possible changes/improvements under the influence of work-hardening and thermal treatments. Since the old/waste copper usually contains little amount of lead and tin, three additional sample materials, such as, copper ingots, copper‑tin alloy, and copper‑lead alloy are taken into consideration to ascertain the influence of individual solder elements on the properties of the copper alloy. It is observed that addition of trace amount of tin and lead can significantly influence micro-hardness, conductivity, thermal capacity, etc. Micro-hardness values of all four sample materials have been found to be increasing in curvilinear pattern with the rise of cold-rolling level up to 50– 55% and then get flatten, and cold-rolled work-hardening level of ~35% is found to be a critical deformation level where the hardness of CuPb alloy supersedes pure Cu and Cu-Sn-Pb alloy supersedes CuSn alloy. Electrical conductivity of Cu falls drastically with the addition of only about 1% Sn or 1% Pb, which increases little initially after cold-rolled deformation up to ~35% and start falling again with the rise of deformation levels. Shifting of endothermic peak has occurred and thereby recrystallization temperature of Cu is transformed as an effect of alloying due to inclusion of SnPb-solder in Cu as well as work hardening. Micrographs have confirmed the structural changes responsible for the variation of electro-mechanical properties.

Microstructure and mechanical properties of Zr55Cu30Al10Ni5 amorphous alloy with high-energy states produced by strip casting

In this work, the twin-roll strip-casting technique was used to produce high-energy state Zr55Cu30Al10Ni5 (at%) amorphous alloy sheets. The effect of the temperatures of the alloy melt on their microstructure during production process was studied. The deformation mechanism of the fabricated pure amorphous alloy sheets, in addition to the effects of the formed crystalline particles in them, on their ductility and strength were investigated through mechanical property tests and in situ observations of their microdeformation and microfracture processes. The results indicated that the formation and growth of crystalline particles in amorphous alloy sheets can be inhibited by increasing the melting and casting temperatures of the alloy melt. The fabricated high-energy amorphous alloy sheets exhibit significant plasticity in compression at room temperature, which was achieved through the sequential formation and cross growth of multiple shear bands. Moreover, the appropriate crystalline particles in the alloys could impede the linear propagation of the shear bands in the initial stage of compression deformation, which makes the alloys exhibit a certain level of work-hardening. However, with the increase in deformation, these crystalline particles became the source of the cracks in the alloys and accelerated their fracturing. Overall, this research provides an effective idea for regulating the microstructure and mechanical properties of amorphous alloys. In addition, it offers a significant guide for the industrial production of large amorphous alloy sheets.

Grinding force and surface quality in creep feed profile grinding of turbine blade root of nickel-based superalloy with microcrystalline alumina abrasive wheels

Creep feed profile grinding of the fir-tree blade root forms of single crystal nickel-based superalloy was conducted using microcrystalline alumina abrasive wheels in the present study. The grinding force and the surface quality in terms of surface topography, subsurface microstructure, microhardness and residual stress obtained under different grinding conditions were evaluated comparatively. Experimental results indicated that the grinding force was influenced significantly by the competing predominance between the grinding parameters and the cross-sectional root workpiece profile. In addition, the root workpiece surface, including the root peak and valley regions, was produced with the large difference in surface quality due to the nonuniform grinding loads along the root workpiece profile in normal section. Detailed results showed that the surface roughness, subsurface plastic deformation and work hardening level of the root valley region were higher by up to 25%, 20% and 7% in average than those obtained in the root peak region, respectively, in the current investigation. Finally, the superior parameters were recommended in the creep feed profile grinding of the fir-tree blade root forms. This study is helpful to provide industry guidance to optimize the machining process for the high-valued parts with complicated profiles.

Effect of type of reinforcing particles on the deposition efficiency and wear resistance of low-pressure cold-sprayed metal matrix composite coatings

Low-pressure cold spraying was used to deposit boron carbide (B4C), titanium carbide (TiC), and tungsten carbide (WC) based metal matrix composite (MMC) coatings. Nickel (Ni) was used as the matrix and each carbide powder was mechanically blended with Ni powder prior to spraying. The average velocity of the carbide particles and their momentum during the cold spray deposition were estimated using a mathematical model. The effect of the carbide particle momentum on the Vickers micro-hardness and wear resistance was evaluated. The model showed that the average momentum of WC particles was more than two times greater than that of B4C particles and almost six times greater than that of TiC particles. The higher momentum of the WC particles led to a higher level of work hardening of the matrix, which resulted in improvement of the hardness and wear resistance of the MMC coatings. This led to similar hardness values for the deposited MMC coatings (400kg/mm2) despite the difference in hardness of the selected reinforcing carbides. Furthermore, it was found that the high momentum and high fracture toughness of the WC particles increased the roughness of the coating surface and compacted the coating, which led to higher deposition efficiency for this carbide-metal powder blend on previously deposited coating layers. The lowest wear resistance was achieved by the WC-Ni MMC coatings due to the higher fracture toughness of WC particles and also work hardening of the Ni matrix. The results obtained emphasize the importance of the carbide fracture toughness and particle momentum on the deposition efficiency, hardness, and wear resistance of cold-sprayed MMC coatings.

Surface integrity of bored super duplex stainless steel SAF 2507

This investigation explores the effect of some input cutting variables of boring process—cutting speed, feed rate, tool nose radius and coolant pressure—on the surface integrity of super duplex stainless steel grade SAF 2507. The surface integrity was evaluated by means of 3D surface roughness, residual stresses determined by X-ray diffraction, and work hardening using Vickers hardness. The most significant variable was the feed rate, which affected both the roughness parameters and the residual stresses. For the low level of feed rate and the higher nose radius tested the machined surfaces could be identified as Gaussian in terms of surface heights distribution with an insignificant work hardening due to the machining. In this fashion, a best combination of boring conditions could be indicated to reach the lowest roughness values with Gaussian surfaces and compressive residual stresses with a low level of work hardening.

Influence of residual stress and work hardening on instrumented indentation

Many forming and surface treatments for metallic materials introduce residual stresses and work hardening simultaneously in mechanical components. Instrumented indentation is a technique which is sensitive to both phenomena and can thus be used to quantify them provided that their influences on the experimental response can be separated. In the present paper, this question was addressed through a series of Finite Elements simulations of a spherical indentation test in which the residual stress and work hardening levels were varied independently. It was found that, for each given value of the compressive residual stress, there is a corresponding work hardening level (cumulated plastic strain) for which the two P -h curves (Force vs. Penetration Depth curves) are almost completely superposed. Therefore, it will be impossible to obtain a unique set of residual stress and work hardening from the analysis of the sole P -h curves. However, when the dimples left by the indenter are analyzed, it can be found that, for the same P -h curve, the two phenomena lead to a difference in pile-up value which is about 2% of the maximum penetration depth. The numerical simulations presented in the paper are obtained on a specific material with a spherical indenter but similar results were obtained on other materials with a spherical or a conical indenter.

Material Modeling of 980 MPa Dual Phase Steel Sheet Based on Biaxial Tensile Test and In-plane Stress Reversal Test

Uniaxial and biaxial tests were conducted to investigate the deformation behavior of dual phase steel sheet with a tensile strength of 980 MPa. Detailed measurements were made of the contours of plastic work and the directions of plastic strain rate at different levels of work-hardening for linear stress paths in the first, second and fourth quadrants in the principal stress space. Cruciform specimens were used in the first quadrant and the pure shear yield stresses in the second and fourth quadrants were measured using combined tension-compression tests. The most appropriate anisotropic yield function for the material was determined by comparing the measured data with those calculated using selected yield functions. In-plane compression tests were also performed using the comb-shaped dies proposed by one of the authors. The measured work contours and directions of plastic strain rates were in good agreement with those calculated using the Yld2000-2d yield function with an exponent of 4. The stress-strain curves measured for the in-plane stress reversal tests were in fair agreement with those calculated using the Chaboche-Rousselier model; however, this model is not capable of reproducing the nonlinear behavior of the material during unloading.

金属薄板の面内に引張圧縮組合せ応力を負荷する<br>材料試験法

An experimental method of applying in-plane combined tension-compression stresses to a sheet specimen is proposed. Comb-shaped dies are specially designed for the tension-compression test and are installed into a biaxial stress-testing machine developed by one of the authors [Kuwabara and Ikeda: J. JSTP, 40-457 (1999), 145-149]. To check the usefulness of the testing apparatus proposed in this study, we carried out biaxial stress experiments using a high strength steel with a tensile strength of 440MPa, and detailed measurements were made of the plastic work contours as below and the directions of the incremental plastic strain vectors at different levels of work-hardening for linear stress paths in the second and fourth quadrants of the principal stress space, as well as in the first quadrant. We found that the measured work contours are similar in shape, and that the directions of the incremental plastic strain vectors remain almost constant at each constant stress ratio. The work contours and the directions of the incremental plastic strain vectors are in close agreement with those predicted using the Hosford or Yld2000-2d yield function.

Ground surface improvement of the austenitic stainless steel AISI 304 using cryogenic cooling

Grinding fluid selection is becoming increasingly constrained by environmental considerations, thus requiring the substitution of the conventionally used oil-based coolants. The work presented in this paper aims at evaluating the ground surface quality improvements of the austenitic stainless steel AISI 304 resulting from the application of cryogenic cooling. The evaluation is based on criteria related to grindability, surface integrity and corrosion resistance characterisation. Grinding experiments at an almost constant stock removal rate were conducted under three different environments: dry, soluble oil and cryogenic cooling. The grindability results have shown that while the cryogenic cooling generates the lowest grinding temperature, no significant differences over the specific grinding force components were observed. As for the ground surface integrity, however, substantial improvements were realized. Indeed, by using the cryogenic cooling, a reduction of more than 40% of the surface roughness could be realized, a higher level of work hardening occurred, a lower level of tensile residual stress was measured and better resistances to stress corrosion cracking and pitting corrosion were noticed. These improvements in grindability and in surface integrity are particularly favoured by grinding conditions using high work speed and low depth of cut values. It is also shown that these improvements are essentially due to the reduction of the grinding temperature, which lowers the tensile residual stress and to the cryo-temperature, which favours the material removal by shearing and limits the ground surface damage.

Similarity and scaling in creep and load relaxation of single‐crystal halite (NaCl)

This work explores the physical basis for Hart's mechanical equation of state in high‐temperature plasticity. The experiments seek to identify a possible microstructural basis for the “hardness” parameters associated with load relaxation curves. The experiments also seek to examine the microstructural basis for scaling in load relaxation data and to explore the relationship between creep and load relaxation. Constant stress creep and load relaxation tests were conducted on [100] oriented single crystals of halite at 700°C and stresses between 0.6 and 3 MPa. Load relaxation tests were performed at 400°C up to a stress level of 13 MPa. After testing, specimens were sectioned, and dislocation densities and subgrain size distributions were measured. Results at 700°C reveal that distributions of subgrain size in crystals crept at different stress levels are similar to each other; that is, they have the same shape but different average subgrain sizes depending on stress level. Hardness curves obtained from load relaxation experiments at different levels of work hardening were found to correspond to different average subgrain size. Load relaxation data from 700°C and 400°C belong to a single‐parameter family of curves, with hardness curves translating onto each other with a scaling slope m = 0.33 ± 0.05. Subgrain size distributions generated in creep are statistically identical to those from load relaxation. The hardness parameter, σ*, specified as the (apparent) high‐strain rate limit of stress in the load relaxation data, is approximately 50Gb/DI, where G is the shear modulus, b is the Burgers vector, and DI is the mean intercept subgrain diameter. During creep under constant stress the subgrain size evolves until a steady value is approached. The experimental data lend credence to Hart's interpretation that load relaxation data represent (nearly) constant “structure” with subgrain size playing the role of the structural variable.

Anisotropic plastic deformation of extruded aluminum alloy tube under axial forces and internal pressure

The anisotropic plastic deformation behavior of extruded 5000 series aluminum alloy tubes, A5154-H112, of 76 mm outer diameter and 3.9 mm wall thickness is investigated, using a servo-controlled tension-internal pressure testing machine. This machine is capable of applying arbitrary stress or strain paths to a tubular specimen using an electrical, closed-loop control system. Detailed measurements were made of the initial yield locus, contours of plastic work for different levels of work-hardening, and the directions of the incremental plastic strain vectors for both linear and combined stress paths. It is found that the measured work contours constructed in the principal stress space are similar in shape, and that the directions of the incremental plastic strain vectors remain almost constant at constant stress ratios. The work-hardening behavior predicted using Hosford's or the Yld2000-2d yield functions under the assumption of isotropic hardening agrees closely with the observations for both linear and combined stress paths. The material is thus found to work-harden almost isotropically. Both yield functions are effective phenomenological plasticity models for predicting the anisotropic plastic deformation behavior of the material.

Stacking fault energy and dynamic recovery: do they impact the indentation size effect?

Aluminum, a high stacking fault energy (SFE) material and α-brass, a low SFE material were tested for the indentation size effect (ISE) using a combination of microhardness (high load) and nanoindentation (low load). Four samples from each material were tested; annealed electropolished, annealed mechanically polished, work-hardened electropolished, and work-hardened mechanically polished. The micro and nano indentations were made using a Vickers and a Berkovitch diamond indenter tips with indentation loads between 0.1–3 (microindentations) and 10 −4–10 −2 N (nanoindentations), respectively. Based on areas measured using optical and scanning electron microscopy in addition to contact stiffness, it is found that the calculated nanohardness increases monotonically with decreasing load or depth of indentation. The work-hardened samples are harder than the annealed ones except for aluminum at shallow indents where it is not possible to distinguish between differences in hardness. All eight samples regardless of the SFE, rate and intensity of cross-slip and dislocation climbing rates (dynamic recovery), and level of prior work hardening of the material, explicitly exhibited an ISE. The magnitude of the ISE is not influenced by SFE, dynamic recovery, or prior level of work hardening. The data are found to behave linearly consistent with the Strain Gradient Plasticity model (SGP) for micro and deep nanoindentations; the shallow nanoindentation data deviated into a second linear behavior constituting what we term a ‘bilinear behavior’.

Indentation size effect in polycrystalline F.C.C. metals

High purity aluminum and alpha brass samples were tested for the indentation size effect (ISE) using a combination of microhardness (high load) and nanoindentation (low load). We employed rate effects to study low temperature deformation mechanisms using nanoindentation creep and load relaxation. Based on these rate effects which are conspicuous in terms of the rate sensitivity of the hardness, ∂H /∂ ln ε ̇ eff , we calculated the activation volume, V ∗ , and compared data from indentation creep with data from uniaxial loading. The data from nanoindentation for alpha brass when plotted, V∗ vs H or τ (flow stress) , extrapolated into literature data from conventional tensile testing, while the aluminum nanoindentation data exhibited an offset. We propose some mechanisms for this offset. We demonstrate that the trend of V ∗ vs H, resulting from the ISE in a single specimen, concurs with that obtained from testing specimens with various levels of work hardening. This suggests that the ISE is driven by a dislocation mechanism. Additionally, when the results are fitted to a strain gradient plasticity model (SGP), the data at deep indents (microhardness and large nanoindentation) exhibited a straight-line behavior closely identical to literature data. However, for shallow indents (nanoindetation data), the slope of the line severely changes, decreasing by a factor of ten, resulting in a “bilinear behavior”. We also propose some possible mechanisms for this behavior.