Back Stress Research Articles

On the microstructural evolution in a 10% Cr martensitic steel during interrupted low cycle fatigue testing at 650 °C

The correlation between cyclic softening and microstructural evolution using the interrupted low cycle fatigue (LCF) tests with a low strain amplitude of ±0.2% at 650 °C in a 10% Cr steel was studied. Cyclic softening was analyzed in terms of the friction and back stresses caused by short-range and long-range obstacles, respectively. Softening was mainly attributed to a decrease in the friction stress due to the dislocation annihilation. Whereas the back stress remained more stable due to additional precipitation on the lath boundaries, despite the intense lath widening caused by the disappearance of lath boundaries.

SANISAND-H: A sand bounding surface model for high pressures

This paper presents a new bounding surface constitutive model for sand, named SANISAND-H, capable of predicting the shear and volumetric behavior of the material under extra-high range of pressures, in addition to normal pressures. The model is an extension of the SANISAND08 model (Taiebat and Dafalias, 2008) with a closed cone-type yield surface that obeys rotational and isotropic hardening. The critical state line and the limiting isotropic compression curve of the SANISAND08 model are modified to accommodate a wide range of pressures. A new constitutive ingredient is the definition of a reference compression curve that serves as bounding surface for establishing the isotropic hardening rule of the yield surface. The kinematic hardening rule and stress-dilatancy relationship of the SANISAND08 model are significantly modified, to better capture the response of sands under high pressure. The value of the back stress ratio at the initiation of a new loading process is re-introduced, ensuring a smooth elastic-plastic transition necessary for accurate simulation of the response under loading reversals. The SANISAND-H model simulations are in very good agreement with test data for Toyoura and Cambria sands under various drained and undrained monotonic stress loading paths in a wide range of densities and pressures.

Modelling of fatigue damage in granitic rock by piezoelectric effect in quartz phase due to alternating current excitation

This paper considers numerical modelling of hypothetical fatigue damage in granitic rock by alternating current (AC) excitation of piezoelectric properties of Quartz. For this end, a numerical method consisting of a rock mineral mesostructure model, an implicit time stepping scheme to solve the piezoelectro-mechanical problem, and a fatigue damage model was developed. The rock material was assumed to be heterogenous linear elastic and isotropic, save the Quartz piezoelectric properties, which are anisotropic. An evolution equation-based continuum scalar damage model based on an evolving back stress tensor and a moving Drucker–Prager type of endurance surface was applied to compute the damage inflicted by the AC excitation. The damage was computed in a post-processed mode, i.e., un-coupled to the material model, at this stage of investigations. Some preliminary axisymmetric simulations are presented with a rock mesotructure based on electron backscatter diffraction data. These simulations corroborate the hypothesis that fatigue damage can be induced on granitic rock by converse piezoelectric effect in the Quartz phase by sinusoidal alternating current. More specifically, fatigue damage was induced on a disc-shaped numerical rock sample at a voltage of 15 kV with 2.5 kHz of frequency.

ID: 221660 Long-Term Chronic Orchialgia Pain Resolution Following Sacral Nerve Stimulation–A Case Report and 5-Year Follow-Up

Chronic Orchialgia (CO) is a neuropathic pain syndrome described as intermittent or constant testicular pain lasting ≥3 months and significantly interferes with daily activities. The pain is typically described as scrotal content pain and may involve one or both testicles, the epididymis, para-testicular structures, and the spermatic cord. CO is most frequently seen in men in their mid to late 30s and has shown increased incidence in recent years. In addition to severe pain, it is associated with male infertility, low back pain, stress, depression, and irritable bowel syndrome. We present a case of paddle lead sacral nerve stimulator implantation effectively resolving CO pain.

Effect of solution annealing temperature on microstructural evolution and mechanical properties of NbC-reinforced CoCrFeNi based high entropy alloys

Recent studies have shown that NbC precipitates in high-entropy alloys (HEAs) are strong obstacles for dislocation motion, which can substantially contribute to the mechanical performance over a wide temperature range. However, there are limited reports discussing the exceptional adjustability of microstructures and mechanical properties using thermomechanical processing (TMP). Therefore, the microstructures and mechanical properties of NbC-reinforced CoCrFeNi based high entropy alloys (HEAs) tuned via TMP were systematically investigated. Homogenized HEAs with ∼0.3 at% C and Nb were solution annealed at 1100, 1200 and 1300 °C, followed by cold-rolling plus annealing. The microstructures and mechanical properties of the HEAs were systematically characterized using scanning electron microscopy, transmission electron microscopy and uniaxial tensile tests. The results indicated that NbC distribution evolved from eutectic-like primary NbC clusters surrounded by disorderly distributed secondary NbC to dispersive nano-sized secondary NbC as the solution annealing temperature increased above the NbC solvus temperature. Two kinds of microstructures were correspondingly produced: 1) samples solution annealed at 1100 and 1200 °C consisted of fine grain lamellae embedded with NbC precipitates and coarse grain lamellae without precipitates, which exhibited a combination of high strength (UTS ∼740 MPa) and good ductility (elongation ∼60%); and 2) samples solution annealed at 1300 °C obtained a homogeneous fine grain microstructure, which demonstrated excellent synergy of high strength (UTS ∼760 MPa) and exceptional ductility (elongation ∼63%). The enhanced strength of samples solution annealed at 1100 and 1200 °C originated primarily from the high back stress strengthening of lamellar microstructure, while precipitation strengthening caused by dispersed nanosized NbC precipitates and grain boundary strengthening provided extra strengthening for the sample annealed at 1300 °C. This work provides a new strategy for tailoring the microstructure and mechanical properties of NbC-reinforced HEAs via adjusting the solution annealing temperature of TMP.

Health and well‐being of sibling carers of adults with an intellectual disability in Ireland: Four waves of data

AbstractBackgroundAs the life expectancy of people with intellectual disability increases, they may now outlive their parents or their parents' ability to continue to care. Siblings of adults with intellectual disability often succeed their parents as primary carers. Little is known about the health and well‐being of this important cohort of carers who will be both caring for and ageing alongside their brother or sister with intellectual disability. The Carer's Study within The Intellectual Disability Supplement to the Irish Longitudinal Study on Ageing (IDS‐TILDA) provides a unique insight into the health and well‐being of family carers of older adults with intellectual disability including sibling carers in Ireland. This article reports on the findings from waves 1, 2, 3 and 4 of the IDS‐TILDA Carer's Study.MethodsThe IDS‐TILDA Carer's Study surveys family carers of older people (aged 40 years and older) with intellectual disability on a 3‐yearly cycle. The family carers complete a self‐administered, mixed‐methods questionnaire. The qualitative data are analysed thematically, and a descriptive analysis of the quantitative data is conducted using SPSS.FindingsIn each wave, sibling carers comprised a significant proportion of the Carer's Study participants: W1 58%; W2: 61.4%; W3: 76.7%; and W4: 45.8%. The siblings were predominantly female, not in paid employment and were caring without the support of a spouse or partner. Across the four waves, siblings reported good general health. However, a high prevalence of particular conditions including back pain, aching joints and stress was also reported, and in each wave, siblings reported feeling completely overwhelmed by their care responsibilities. Although sibling carers reported that they have considered the future, only a minority have progressed to action in this regard.ConclusionsThere is evidence of the strong relational and emotional commitment by the siblings to their brother or sister with intellectual disability. However, through the four waves of data, there was also evidence of physical, mental and financial toll. An urgent need exists to identify and engage with siblings to protect their well‐being as they provide care for an increasingly ageing sibling.

The role of Ca on the microstructure and tensile properties of Mg-Al-Zn-Ca alloys

Synergy between Ca and other alloying elements such as Al and Zn can modify the microstructure and mechanical properties of Mg alloys. In this work, we compared four extrusion alloys: Mg-6Al-2 Zn, Mg-6Al-2Zn-0.5Ca, Mg-6Al-2Zn-1.0Ca, and Mg-6Al-2Zn-2.0Ca (all in wt.%). Tensile properties were remarkably not improved with Ca addition. The underlying reasons were explored using in situ synchrotron X-ray diffraction, electron microscopy, and cyclic loading tests. It is found that solute Ca imposes a softening effect on Mg's slip systems. The slight increase of the yield strength by the formation of Al2Ca particles is fully offset by the reduced Al solute strengthening. Texture weakening and resultant ductility enhancement reported in Mg-Zn-Ca ternary alloys is largely compromised by the high amount of Al. Nevertheless, Al2Ca particles can enhance the materials’ strain hardening by inducing back stress. An elastic-viscoplastic self-consistent (EVPSC) model was employed to simulate the deformation of the four alloys. Discrepancies between the simulation results and the experimental measurements mostly occur in the microscopic level (e.g. lattice strains and dislocation density evolution), and the reasons will be discussed.

A longitudinal gradient architecture achieves better tensile properties in Ti6242 alloy

Simultaneous increase in strength and ductility is obtained in Ti6242 alloys using a longitudinal gradient structure. Such architecture demonstrates strain hardening regarding the gradient layer's volume fraction (Vf). The maximum strain hardening is produced in the freestanding gradient layer (Vf = 100%). An extra strain hardening evidenced by the increased back stress occurs in gradient samples, which partly accounts for the concurrently improved properties. Additionally, more boundaries of the α/β plates in lamellar structure and increased dislocations in the primary α phase (αp) are responsible for the enhanced strength. In the gradient layer, such microstructural characteristics, including significant thinning of the β plates, the locally disappeared boundaries of αp and transformed β structure (βt), and the reduced property difference between deformed αp and βt, contribute as well on the ductility improvement. This work provides a guideline for manufacturing high-performance Ti alloys via microstructural regulation or gradient architecture.

Origins of strengthening and toughening effects in twinned nanocrystalline alloys of low stacking fault energy with heterogeneous grain structure

Low stacking-fault energy (SFE) nanocrystalline alloys with pre-existing nanotwins (PNTs) and heterogeneous grain structure (HGS) exhibit exceptional strength-ductility combinations. This has been mainly ascribed to the multiple concurrent deformation mechanisms promoted by the low SFE, and back stress hardening from the strain gradient imposed by PNTs and HGS via activities of geometric necessary dislocations (GNDs). However, the influence of PNTs on dislocation configurations, and the role of intragranular statistically stored dislocations (SSDs) in the mechanical response are still unclear. Here, we uncover the origins of strengthening and toughening effects in a prototype low SFE multicomponent CoCrNi alloy with PNTs and HGS via atomistic simulations. The results show that HGS leads to significant strain partitioning between the smaller- and larger-grain domains and promotes the strain localization, while PNTs alleviate the strain localization and facilitate homogeneous deformation for better toughness. Moreover, PNTs efficiently block intragranular mobile Shockley partials and enhance the dislocation reaction probability, increasing the densities of sessile SSDs. The strengthening effects from both, dynamically increased sessile structures and plastic resistance induced by localized dislocations, are revealed by quantitative analysis on dislocation distributions. This indicates that the dislocation configurations correlated with strain localization are fortified owing to the presence of PNTs and HGS, which further enhance the flow stress on deformation. The present study demonstrates that, PNTs can enable efficient controlling of dislocation configurations upon deformation, while the strengthening and toughening effects of alloys with heterostructures are achieved by both GNDs correlated with localized strains and SSDs generated via dislocation reactions.

Influence of thermomechanical treatment on the shape memory effect and pseudoelasticity behavior of conventional and additive manufactured Fe–Mn–Si–Cr–Ni-(V,C) shape memory alloys

This study evaluated the influence of heat treatment and thermomechanical training on the microstructural evolution and mechanical characteristics of conventional and additive-manufactured FeMnSi-based shape memory alloys. The conventional samples were produced by casting and rolling. The additive-manufactured samples were manufactured using the laser powder bed fusion (L-PBF) technique. Both specimens were subjected to the same heat treatment and thermomechanical training. The heat treatment involved solution annealing at 1050 °C for 2 h and aging at 750 °C for 6 h, and the thermomechanical training concluded with a 4% elongation at ambient temperature followed by annealing at 250 °C for 15 min. This training cycle was repeated four times for each sample after heat treatment. The heat treatment improved the pseudoelasticity and shape memory effect of the samples. Although training further enhanced the pseudoelasticity, it also reduced the shape memory effect. Thermomechanical training led to the formation of a large number of stacking faults, which facilitated the inverse phase transformation of martensite (ε) to austenite (γ) during unloading, resulting in improved pseudoelasticity. The heat-treated additive-manufactured samples showed the highest total recovery strain owing to the pseudoelasticity and shape memory effect. This characteristic could be due to the smaller grain size and higher volume fraction of precipitates. The precipitates and grain refinement improved the conditions for partial dislocation motion by increasing the back stresses on the martensite tip.

Cyclic deformation mechanism and fracture behaviour of 316L stainless steel under thermomechanical fatigue loading

Thermomechanical fatigue (TMF) behaviour of 316L is investigated based on the internal stress and microstructural characterization at various cyclic stages. Results reveal that the cyclic stress response shows initial hardening followed by cyclic softening at a high strain amplitude, while presenting continuous cyclic hardening as the strain amplitude decreases. Among these, Out-of-phase TMF always shows cyclic softening irrespective of strain amplitude. It is important to note that the hardening of back stress and friction stress contribute to the initial and subsequent cyclic hardening. In contrast, the subsequent cyclic softening is mainly dominated by the reduced friction stress. It is observed that the proliferation of dislocations at grain boundaries and the enhanced dislocation interactions within the grains are primarily responsible for the hardening of back stress and friction stress, respectively. Specifically, the cyclic softening of friction stress is attributed to the annihilated dislocations as a result of cross-slip. It is also found from the hysteresis curves that the intensity of dynamic strain ageing is related to strain amplitude, loading history and phase angle, which correlates to the occurrence of cross-slip, the diffusion rate of the solute atom, the density of point defect and the mobility of vacancies. Finally, the effect of loading conditions on fracture behaviour is demonstrated from the point view of crack sources, secondary cracks, creep cavities and oxidation damage.

Enhanced strength-ductility synergy in NbC-reinforced FeMnCoCr high entropy alloy with heterostructure by adopting a novel process

We explored a novel heterostructure design strategy to simultaneously enhance the strength and ductility of NbC-reinforced FeMnCoCr high-entropy alloys by adopting grain-scale strain localization regulation coupling partial recrystallization annealing, and the effect of cold-rolled microstructure on annealed microstructure evolution and mechanical properties was studied. The transformation-induced plasticity (TRIP) effect and the dislocation density decreased as the grain size increased. The significant grain-scale strain localization and obvious Brass and A textures were observed in the cold-rolled microstructure of the large grain samples. Recrystallization preferentially occurred in the high-strain region during annealing leading to heterogeneous recrystallization nucleation. The recrystallization kinetics of A texture was slow and remained in the partially recrystallized microstructure. A heterostructure with a bimodal grain size distribution was formed in coarse-grained samples. The heterostructure with coarse un-recrystallized grains wrapped by recrystallized grains has good comprehensive mechanical properties. Its yield strength was 1.4 times that of a fine-grained microstructure sample, while maintaining excellent strain hardening capacity without decreasing elongation. The high yield strength was attributed to dislocation strengthening. The TRIP effect appeared earlier in the coarse un-recrystallized grains with low dislocation density under tension, and the back stress strengthening and TRIP effect improved the strain hardening capacity.

Enhanced strength-ductility balance of the (CoCrFeNiMn)95.2Al3.2Ti1.6 high-entropy alloy by co-precipitation of the B2 and sigma phases

The present work investigated the effect of the co-precipitation of the B2 and σ phases on the mechanical properties of the (CoCrFeNiMn)95.2Al3.2Ti1.6 high entropy alloy subjected to two-step annealing. The single-step annealed sample at 900 °C only showed B2 precipitates. Further annealing at 650 and 750 °C led to the co-precipitation of σ and B2 particles. The sizes and fractions of σ and B2 particles increased with increasing annealing temperature. The sample subjected to the second annealing at 750 °C, with large sizes and fractions of co-precipitated σ and B2 particles, exhibited high strength with maintaining moderate ductility (YS: 561 MPa, UTS: 1005 MPa, TE: 26%). The superior mechanical properties of the sample subjected to the second annealing at 750 °C could be owing to the co-precipitation hardening, back stress strengthening, joint activation of dislocation plasticity and deformation twinning. The present work offers a novel microstructure design to optimize the strength–ductility balance of high-entropy alloys via the co-precipitation of σ and B2 particles.

Cyclic stress response and microcrack initiation mechanism of modified 9Cr‐1Mo steel under low cycle fatigue at room temperature and 350°C

AbstractTo investigate the effect of temperature on microcracking mechanisms of modified 9Cr‐1Mo steel, low cycle fatigue tests were performed at 350°C and room temperature (RT). At RT, the cyclic stress response at low strain amplitude (<0.5%) is controlled by friction stress while dominated by back stress at high strain amplitude. By comparison, the disappearance of sub‐grain boundaries induced by dislocation annihilation occurs at 350°C, which contributes to the decrease in back stress, resulting in more significant effects of back stress compared to RT. As a result of the accumulated fatigue damage, the distance between two parallel extrusions at 350°C is larger than that at RT, which is ascribed to the disappearance of low angle sub‐grain boundaries due to dislocation annihilation at 350°C. Due to the disappearance of small‐angle grain boundaries at 350°C, microcracks initiate along high‐angle grain boundaries at 350°C instead of along low‐angle grain boundaries at RT.

Parental Obesity: The Pandemic of Intergenerational Physical and Mental Health Carnage

A review of the maternal and paternal impact of obesity at conception on the subsequent health of the offspring paints a nightmarish future in terms of suffering and out-of-control healthcare spending. Consequences of parental obesity on the offspring include obesity, type 2 diabetes, cardiovascular disease, chronic kidney disease, stroke, and premature death. Children of obese women tend to have high blood pressure, left ventricular thickening, increased abdominal fat mass, hyperlipidemia with reduced high-density lipoprotein levels, increased aortic root diameter, insulin resistance, and elevated inflammatory markers, which culminate in a threefold greater risk of cardiometabolic complications than in children of normal-weight mothers. Babies are at greater risk of developing asthma, autism spectrum disorder, attention deficit hyperactivity disorder, cognitive delays, inflammation, cerebral palsy, epilepsy, and the chronic diseases of obesity (such as insulin resistance, high blood pressure, atherosclerosis, cardiovascular disease, stroke, some cancers, including breast, endometrial, and colon cancer, gall bladder disease, polycystic ovarian syndrome, musculoskeletal problems such as osteoarthritis and back pain, gout, cataracts, stress incontinence, and sleep apnea), as well as psychiatric disorders including substance abuse. All parents desire healthy babies, as does society, to avoid the health costs and consequences of our obesity pandemic, but significant personal, societal, public policy, economic, and marketplace interventions will be necessary to avert further devastating impacts. We need to publicize the intergenerational harm caused by obesity, offer support to individuals to help change eating habits and produce a healthier food chain for the nation. Interventions fashioned after the twelve-step program of Alcoholics Anonymous and the adoption of a low carbohydrate abstinence model have proven effective. The time has come to spread the research findings concerning obesity and intergenerational obesity. that are long-accepted by the scientific community but still not recognized by the public at large so that another generation is not impacted by lifestyles that have continuously worsened since the 1970s.

Exploring nonlinear strengthening in polycrystalline metallic materials by machine learning methods and heterostructure design

To improve the strength and plasticity of structural materials, researchers often introduce various strengthening mechanisms such as second-phase strengthening, dislocation strengthening, and back stress strengthening (HDI). Due to the interaction of multiple mechanisms, the linear superposition relationship has a poor fitting effect and is only used for rough calculations of the strengthening mechanisms. In this study, the transfer learning data was used to optimize the deep learning network structure (Re-CNN) based on the residual algorithm, and the yield strength prediction physical neural informed model (PNIM) of polycrystalline metallic materials was established. To promote the industrial application of the heterostructure design method, a medium carbon steel heterostructure design strategy based on the existing equipment of the factory was proposed. Medium-carbon heterostructure materials (MHSM) with mixed strengthening mechanisms were successfully prepared. MHSM exhibits excellent comprehensive mechanical properties. When a linear relationship is used to describe the MHSM yield strength, there is a large error, while Re-CNN shows satisfactory prediction accuracy. The linear relationship is incompatible with homogeneous structure materials and heterogeneous structure materials, and its universality is lower than that of nonlinear Re-CNN. Re-CNN shows high cross-scale prediction ability and can be compatible with homogeneous microstructures and heterogeneous microstructures. Using the heterogeneity evolution characteristics of MHSM, the key factors deviating from the linear relationship were revealed. The overestimation and underestimation of the linear relation are demonstrated by Taylor factor and TEM analysis to be caused by the multiscale properties of ferrite, the behavior of the second phase particles, and the interaction of various mechanisms. This study provides a new idea for the cross-scale calculation of the mechanical properties of polycrystalline metallic materials.

Multi-mechanism constitutive model for uniaxial ratchetting of extruded AZ31 magnesium alloy at room temperature

A multi-mechanism macroscopic phenomenological constitutive model is established to characterize the uniaxial ratchetting of extruded AZ31 magnesium (Mg) alloy at room temperature in the framework of small deformation. Because the uniaxial ratchetting of the alloy depends greatly on the strong basal texture and different deformation mechanisms (i.e., dislocation slipping, twinning and detwinning) and presents apparent tension-compression asymmetry, two separated yield functions and different hardening rules are used in the proposed model regarding to different deformation mechanisms. That is, the traditional von Mises yield criterion and a flow rule in power-law form are used for the plasticity contributed by dislocation slipping, while the Cazacu–Barlat–Plunkett (CPB) yield criterion extended with a back stress tensor and an internal variable f (i.e., twin volume fraction) is employed to express the plastic deformation induced by twinning/detwinning. In addition, the modified Armstrong-Frederick (A-F) kinematic hardening models are adopted to reflect the strain hardening features contributed by different plastic mechanisms, and the interaction among different plastic mechanisms is considered in the developed constitutive model. The reproduced uniaxial ratchetting of extruded AZ31 Mg alloy by the proposed multi-mechanism constitutive model is in a good agreement with the corresponding experimental results obtained at room temperature, which validates the reasonability and capability of the proposed model.

Stored energy density research on the fatigue crack initiation at twin boundary and life prediction of Inconel718 superalloy

The fatigue crack initiation at twin boundary (TB) and the life prediction of IN718 alloys in the high cycle fatigue (HCF) regime and very high cycle fatigue (VHCF) regime were investigated through crystal plasticity finite element (CPFE) simulations and experiments. The fatigue damage parameter, considering the evolution of geometrically necessary dislocation (GND) density, slip and back stress, known as the back-stress-based stored energy density in this study, Gba, was proposed to precisely characterize the plastic strain distribution and localization, which in turn was engaged in locating fatigue crack initiation site and predicting the fatigue life. The element analysis around TB and the CPFE simulations indicated the coupling of slip activation parallel to the TB and the absence of primarily strengthening phase (γ'') on the both side near the TB was responsible for crack initiation. To predict fatigue life, the varying pattern of the Gba at fracture with fatigue life was studied based on the experimental results in the HCF and VHCF regimes, and the life prediction method was obtained accordingly. Finally, the fatigue life evaluations of the IN718 alloy at three load ratios (R = −0.1, 0.1, and 0.5) were conducted and results showed that the life estimates were basically within ±3 scatted bands.

Dispersed strain bands promote the ductility of gradient nano-grained material: A strain gradient constitutive modeling considering damage effect

Gradient nano-grained (GNG) metals have achieved superior strength-ductility synergy than their homogeneous counterparts. The high strength is usually attributed to the grain size effect and hetero-deformation-induced strengthening. However, incommensurate work on ductility leads to an incomplete understanding of the strength-ductility combination. In this work, a dislocation density-based strain gradient plasticity model coupling with a damage model is developed to describe the strain hardening and softening behavior of GNG material. A grain size-dependent back stress model derived from the generation of dislocation pileups is invoked to describe the widely-concerned back stress hardening. Finite element implementation of the model quantitatively predicts the tensile response of GNG nickel with various degrees of grain size gradient. The results reveal that dispersed strain bands propagate stably in the nano-grained surface layer of GNG material, which is totally different from those occurring in a freestanding nano-grained material. The stabilization of dispersed strain bands enables the nano-grained layer to deform uniformly, thus premature failure of the whole GNG material is suppressed and improved ductility is achieved. Furthermore, increasing the grain size gradient renders the strain bands more stable, leading to enhanced ductility. The method developed in this work is helpful for understanding the strength-ductility synergy of GNG materials and for optimizing the microstructure gradient in GNG materials.

Trans-twin dislocations in nanotwinned metals

The strength-controlling dislocation mechanism of a material can be illuminated by partition of the flow stress into its effective stress and back stress components. Recent experiments report a nearly constant saturated effective stress of about 100 MPa for nanotwinned Cu with a range of nanotwin thicknesses less than 100 nm [Z. Cheng et.al., Proc. Natl. Acad. Sci. U.S.A. 119 (2022) e2116808119]. This surprising result implies that the effective stress is controlled by the long dislocations spanning multiple nanotwin lamellae, termed trans-twin dislocations, rather than the commonly thought threading dislocations confined within individual nanotwin lamellae. Here we use molecular dynamics to simulate the formation and motion of trans-twin dislocations across multiple nanotwin lamellae. We show that the interconnected segments of a trans-twin dislocation can glide concertedly on the corrugated {111} slip planes in consecutive nanotwin lamellae with little resistance from coherent twin boundaries. Our results indicate that the finite resistance to slip transmission across coherent twin boundaries can set a lower limit of the effective obstacle spacing to hinder dislocation glide and thus dictate the upper limit of the saturated effective stress of nanotwinned metals. This work provides new understanding of the strength-controlling mechanism in nanotwinned metals.