Stress Direction Research Articles

Stress Characteristics and Mechanical Behavior of Rock Masses with an Opening under Complex Deep Underground Stress Conditions

In this study, the impact of principal stress states on the stress characteristics and initial failure of the rock mass surrounding a three-center arch opening was investigated using complex variable function methods and Discrete Element Method (DEM) numerical modeling. First, the mapping function of the opening was determined using the trigonometric interpolation method, and the influence of the number of terms in the mapping function on its accuracy was revealed. Based on this, the far-field stress state of the underground rock mass was characterized by the ratio of the minimum to maximum principal stress (λ) and the angle (β) between the principal stress and the vertical direction. This stress state was then converted into normal and shear stresses. Using complex variable function theory, the stress characteristics at the boundary of the opening under different stress states were analyzed. Finally, DEM numerical modeling was employed to study the initial failure characteristics at the boundary of the opening and its relationship with the stress distribution. The results indicate that the lateral pressure coefficient significantly affects the stability of the opening by influencing stress concentration around the surrounding rock. Low lateral pressure coefficients lead to tensile stress concentration at the boundary perpendicular to the maximum principal stress. As the coefficient increases, tensile stress decreases, and compressive stress areas expand. While the principal stress direction has a minor effect on stress concentration, it notably impacts stress distribution at the boundary. When λ < 1.0 and β = 45°, stress distribution asymmetry is most pronounced, with the highest compressive stress. The early failure distribution aligns with stress concentration areas, validating the use of stress analysis in predicting opening stability and failure characteristics.

Abrupt structural deformation changes from the boundary to the interior of a craton basin: Implications for the long-term stability of cratonic blocks

Stable intraplate cratonic blocks usually have less structural deformation and fewer earthquakes than other locations on Earth, but with strong compressional deformation around their periphery. Investigating how and why this different deformation occurred is beneficial for understanding why the cratonic block is so stable and how the intraplate in-plane stress is transmitted. In this work, we first investigated the structural deformation changes from the margin to the interior of the western Ordos block (one of the most tectonically stable areas in China) via seismic data. The results show abrupt structural deformation changes from the margin to the interior of the Ordos block in terms of the deformation strength (from strong to weak), structural orientation (high-angle oblique relationships), and kinematics (from compression to wrenching). Our investigation also shows that such phenomena are widespread in cratonic blocks worldwide. The abrupt changes are probably induced by special in-plane stress transfer inside the cratonic block: When far-field stress is transmitted into continental interiors from active plate margins, the weak belt around the cratonic block filters and accommodates the in-plane stress. Consequently, this decreases the stress, changes the stress direction, and transmits the in-plane stress along a shallower layer (probably less than 1500 m). Furthermore, the compressional stress from the plate margin is converted into shear stress within the cratonic block. This stress transmission manner makes reactivation of deep preexisting faults difficult under far-field horizontal plate-boundary stresses in the cratonic block without vertical forces from the mantle, guaranteeing long-term stability and low seismicity. This understanding can provide a new perspective for the interpretation of earthquakes in stable continental regions. It can also be applied to appraise the long-term stability of sites for the storage of CO2.

Characterization and modeling of biaxial plastic anisotropy in metallic sheets

The anisotropic behavior of cold-rolled sheet metals has been extensively studied, typically characterized by uniaxial loading tests in different directions to determine yield strengths and plastic flow (Lankford r-values). However, biaxial principal stress states often focus solely on yield loci in the RD/TD (rolling/transverse) directions, with limited studies on other loading directions. This study analyzes the relationship between the principal stress yield loci and the material principal anisotropic stress directions based on the Hill48 yield function. Biaxial tensile tests are conducted on DP590 high-strength steel using cruciform specimens cut in various directions different from the sheet RD/TD directions. The evolution of the anisotropic yield locus and plastic flow of DP590 under biaxial tensile directions beyond the traditional RD/TD anisotropic directions is revealed. Furthermore, a modified Hill48 model that considers any principal stress direction of loading is proposed, accurately describing the continuous evolution of equi-biaxial tension stress, near-plane strain stress, and plastic flow direction for different principal stress directions of loading. The issues of failing to predict plastic flow under biaxial loadings in the original Hill48 model, and the degraded representation of existing constitutive models when accounting for out-of-plane anisotropy are addressed by decoupling the relationship between anisotropic parameters and stress state. In addition, the proposed calibration strategy of anisotropic parameters, using experimental data from various principal stress directions of loading, effectively captures the anisotropic evolution caused by changes in principal stress directions. Comprehensive evaluation and verification of the plasticity model should consider yield locus for any principal stress directions of loading, and also the normal and shear planes.

Continuous and synchronous calibration process of ovality and straightness for longitudinally submerged arc welding pipes with three rollers.

A new process of continuous and synchronous calibration process of ovality and straightness for LSAW (Longitudinally Submerged Arc Welding, LSAW) pipes with three rollers is proposed. Specifically, the process is introduced from three aspects: roller-shape, loading parameters and axial and circumferential deformation paths. The process is verified by numerical simulation and physical experiments. Further, the stress-strain in the Sections Ⅱ and Ⅳ is analyzed. The relationship between the process parameters and the residual ovality and residual straightness by experiments is discussed. The calibration scheme of LSAW pipes is put forward by using the control variable method. The results show that the shear stress is the principal stress direction in the Sections Ⅱ and Ⅳ. The residual ovality and residual straightness decrease with the increase of the radial reduction and times of reciprocating bending. The reciprocating bending process can eliminate the difference of the initial curvature, make the curvature of each section tend to be uniform. After calibration, the residual straightness is less than 0.2% and the residual ovality is less than 1%, demonstrating a good feasibility of this process.

Influence of stress and geology on the most prone time of rockburst in drilling and blasting tunnel: 25 tunnel cases

Rockburst exhibits different occurrence time characteristics during drilling and blasting in tunnel excavation, posing challenges to the safe and efficient construction of tunnels. In this study, 25 tunnels with rockburst hazards were examined. By employing the clustering method, we analyzed the characteristics of the most prone time (MPT) for rockburst. Furthermore, we investigated the contribution degree and influence mechanism of stress and geological factors related to the MPT of rockburst. The outcomes revealed that distinct tunnels exhibit diverse rockburst-prone times, leading to varying hazards and losses. The higher the maximum principal stress and the angle between it and the tunnel axis, the earlier the rockburst occurs. Moreover, the MPT of rockburst is influenced by both lithological types, macro and micro rock structures. When the joint intersects with the maximum principal stress at a small angle, rockburst occurs earlier. The stress direction, UCS, attitude of the dominant joint, and stress magnitude stand out as the principal controlling factors. The findings of this research can serve as a basis for assessing the MPT of tunnel rockburst, timing rockburst risk control measures, and selecting appropriate mitigation strategies.

Ultrasonic measurement method for three-dimensional assembly stress of aero-engine rotors

The precise measurement of three-dimensional stress in the rotor is a key means to ensure the assembly accuracy and operational safety of aero-engines. The unclear coupling influence mechanism of different directions of stress on ultrasonic propagation makes it challenging to establish a three-dimensional stress measurement model. This paper proposes a three-dimensional assembly stress measurement method for aero-engine rotors based on ultrasonic propagation time difference decoupling. The three-dimensional assembly stress is converted into the stress component parallel and perpendicular to the ultrasonic wave propagation direction in this method. The acoustoelastic equation including three-dimensional stress parameters is established based on the function model of different direction stress and ultrasonic wave propagation velocity. An innovative three-transducer stress measurement scheme is designed, which integrates ultrasonic wave transmitting and receiving transducers and time difference feedback transducers. The acoustoelastic equations in three propagation directions are constructed by rotating the transducer group to change the propagation direction of ultrasonic waves. Finally, the acoustoelastic equations are solved simultaneously to decouple the ultrasonic propagation time difference, thus achieving a three-dimensional assembly stress measurement of the aero-engine rotor. The experimental results show that the maximum deviation between the measured values and the simulation results in the x ,y, and z directions is 15.885 MPa, 14.113 MPa, and 17.093 MPa, respectively. This study provides effective theoretical and technical support for precisely measuring three-dimensional assembly stress in high-end equipment represented by aero-engines.

An analytical modelling of the rotation of in-situ principal stresses orientation in the vicinity of an underground opening

ABSTRACT An underground excavation would lead to the redistribution of not only stress magnitude but also stress direction in the host rock mass. In this paper, an equation was derived to quantify the principal stress orientation rotation angle along the roadway radial direction. Besides, the principal stress orientation rotation gradient was analytically modelled followed by a sensitivity analysis of various influential factors on the principal stress orientation rotation. It was found that the principal stress orientation rotation angle tends to decrease as moving further radially into the rock mass from the excavation surface, where the principal stress rotation angle reaches its maximum value of 90°. Four zones have been classified according to the principal stress orientation rotation gradient including high-frequency , medium-frequency, low-frequency and no rotation zone. Finally, the numerical analysis confirmed the redistribution of the principal stress difference and the rotation angle and provided guidance for optimising the bolts setting angle.

Seismicity associated with hydraulic fracturing in Changning shale gas field, China: Constraints from source mechanisms, stress field and fluid overpressure thresholds

Source properties and stress fields are critical to understand fundamental mechanisms for fluid-induced earthquakes. In this study, we identify the focal mechanism solutions (FMSs) of 360 earthquakes with local magnitude ML ≥ 1.5 in the Changning shale gas field from January 2016 to May 2017 by fitting three-component waveforms. We then constrain the directions of the maximum horizontal stress (σHmax) for four dense earthquake clusters using the stress tensor inversion method. The stress drops of 121 earthquakes with ML ≥ 1.5 are calculated using the spectral ratio method. We examine the spatiotemporal heterogeneity of stress field, and discuss the cause of non-double-couple (non-DC) components in seismicity clusters. Following the Mohr-Coulomb criterion, we estimate the fluid overpressure thresholds from FMS for different seismic clusters, providing insights into potential physical mechanisms for induced seismicity. The FMS results indicate that shallow reverse earthquakes, with steep dip angles, characterize most events. The source mechanisms of earthquakes with ML ≥1.5 are dominated by DC components (> 70%), but several earthquakes with ML > 3.0 and the microseismic events nearby during injection period display significant non-DC components (> 30%). Stress inversion results reveal that the σHmax direction ranges from 120° to 128°. Stress drops of earthquakes range between 0.10 and 64.49 MPa, with high values occurring on reverse faults situated at a greater distance from the shale layer, accompanied by a moderate rotation (≤ 25°) in the trend of σHmax. The seismic clusters close to the shale layer exhibit low fluid overpressure thresholds, prone to being triggered by high pore-pressure fluid. The integrated results suggest that the diffusion of high pore pressures is likely to be the primary factor for observed earthquakes. The present results are expected to offer valuable insights into the origin of anomalous seismicity near the shale gas sites.

A DFT study of the CaMg2As2 material for photovoltaic applications

The research focused on investigating the structural, elastic, electronic, optical, and thermoelectric characteristics of the CaMg2As2 compound. To inspect these properties, the density functional theory (DFT) method has been applied via the Wien2K code. The electronic analysis revealed that the CaMg2As2 compound demonstrates semiconductor behavior with an indirect band gap of 1.781 eV. Additionally, its elastic properties were examined, revealing a 1.980 % AVR, indicating a variation in elasticity depending on the direction of load or stress applied. We have also studied various optical properties of CaMg2As2, including the refractive index, extinction coefficient, electron energy loss, dielectric tensor, and optical conductivity. the absorption coefficient value is zero for energy levels below 2.60 eV, meaning there is no energy absorption by the material at lower energy levels. However, as the energy surpasses 2.60 eV, the absorption coefficient increases and shows multiple peaks. This signifies that as the incident radiation's energy increases, the material starts absorbing more energy at specific energy levels. In addition, one significant finding is that the thermal conductivity of the lattice (κL) in CaMg2As2 decreases exponentially as the temperature rises. This means that as the material gets hotter, its ability to conduct heat becomes less effective. In simple terms, the material becomes less efficient at transferring heat at higher temperatures. These findings suggest that CaMg2As2 has potential as a thermoelectric material with interesting properties that deserve further investigation.

Fatigue Behaviour and Life Prediction of YSZ Thermal Barrier Coatings at Elevated Temperature under Cyclic Loads

The concentration of interfacial normal stress at the free edges of thermal barrier coatings (TBCs) can result in coating spallation. Fatigue cracking is one of the main reasons for creating free edges under complex loads. It is crucial to investigate the fatigue cracking of coatings under cyclic loads to assess potential coating failure. To address this issue, a novel model was proposed to predict the fatigue life of the YSZ topcoat under stress parallel to the interface. Firstly, this study conducted uniaxial and tensile-torsional fatigue tests at elevated temperatures on specimens with atmospheric plasma-sprayed TBCs. The test results revealed that fatigue cracks appeared in the topcoat under cyclic loads, but these cracks did not propagate into the bondcoat or substrate immediately. The number of cycles before the topcoat cracked was found to be associated with the magnitude of the cyclic load. Secondly, this study analyzed the test conditions using the finite element method. Simulations indicated that the crack direction in the topcoat under complex loading conditions was aligned with the first principal stress direction. Finally, the fatigue life prediction model of the topcoat was established based on experiments and simulations. The predicted results fell within a fourfold scatter band.

Analysis of mechanical properties of rice particle beds in confined compression tests and stress transfer predictive model

High-stress breakage during storage and processing is one of the primary factors in the decline of rice quality. To reveal the mechanical response law under this condition, confined compression and numerical simulations were used to analyze the mechanical evolution laws of rice particle beds under high-pressure in this work. The results show that the compaction process progresses from top to bottom. The total number of contact forces in the particle beds increases, the strong contact forces exhibit a diffusion in direction. The maximum principal stress is consistent with the direction of the strong force chain, particle breakage direction corresponds to the maximum principal stress direction. Finally, based on the analysis of the particle beds, a uniaxial confined compression axial stress transfer model for rice particle beds is proposed. The results are helpful for understanding the stress transfer characteristics of rice particle beds, provide basis for the improvement of related equipment.

Re-orientation of principal stresses during tunnel excavation: Model development and support strategy

The safety and stability during the excavation and production of the tunnel is a key issue that must be addressed in tunneling engineering, which is pronounced under principal stress re-orientation. A mechanical model is therefore developed to determine the boundary curve of the failure zone of a supported circular tunnel under rotating the principal stress direction. Meanwhile, the effects of various environmental factors on the pattern of the failure zone are quantitatively analyzed. Subsequently, two critical morphological indexes are determined to elucidate the uniformity of the failure zone and the functional relationship between these two morphological indices and the environmental factors, respectively. Furthermore, technical approaches and control measures for maintaining the surrounding rock are put forward. In particular, the “long and short” coordinated hierarchical support technology has been recommended and is validated through a comparison of the designed schemes and several engineering cases. The results indicate that the proposed support technology resulted in a gradual reduction of the “butterfly wings” pattern and a more consistent failure zone in the surrounding rock. These findings are useful to ensure the overall stability and anti-interference performance of the surrounding rock of a tunnel under the complicated stress field, especially with regards to the deflection of principal stress.

Effect of the hot forming with synchronous quenching process on high cycle fatigue properties of the 2A97 Al-Li alloy

The 2A97 Al-Li alloys have been used in aircraft to achieve lightweight, its high cycle fatigue performance is one of the important factors that determines aircraft safety. The 2A97-T8 Al-Li alloy is obtained through the 2A97-T3 Al-Li alloy undergoes the hot forming with synchronous quenching process. The 2A97-T3 and 2A97-T8 Al-Li alloys are tested for high cycle fatigue under different stress amplitudes. The fatigue crack propagation path of the 2A97-T3 Al-Li alloy is not only along the direction of maximum shear stress at 45° to the stress direction but also along the direction perpendicular to the stress axis. The fatigue crack propagation path of the 2A97-T8 Al-Li alloy propagates along the direction perpendicular to the stress axis. Under high amplitude stress, the characteristics of quasi-cleavage fracture are found in the fracture morphology of 2A97-T3 Al-Li alloy. However, the characteristics of cleavage fracture are found on the fracture morphology of 2A97-T3 Al-Li alloy under low amplitude stress. Under high amplitude stress, the quasi-cleavage characteristics and the dimples are found on the fracture morphology of 2A97-T8 Al-Li alloy. Under low amplitude stress, the small voids and the dimples are found on the fracture morphology of 2A97-T8 Al-Li alloy. The precipitated phases of the 2A97-T3 Al-Li alloy are multitudinous, fine, and dispersed δ’ phases and a few T1 phases. The precipitates of the 2A97-T8 Al-Li alloy are large, fine, and acicular T1 phases and a few δ’ phases. The hot forming with synchronous quenching process significantly improves the high cycle fatigue properties of the 2A97 Al-Li alloy. In addition, the fatigue cycles, the fatigue life rise and fall plots, the S-N curves, and the fatigue crack growth behaviors of the 2A97-T3 and 2A97-T8 Al-Li alloys are obtained.

Research on crack distribution characteristics and control technology of surrounding rock in soft rock roadway under different lateral pressure coefficients

AbstractTo solve the problem of controlling large deformation of surrounding rock in deep soft rock roadway, the distribution characteristics and deformation mechanism of surrounding rock cracks in soft rock roadway under different lateral pressure coefficients are studied using numerical simulation, theoretical analysis, and field measurement. The results show that under different lateral pressure coefficients, the range of surrounding rock cracks shows three forms: round, oval, and butterfly. No matter what lateral pressure coefficient the roadway is in, the surrounding rock cracks always appear in the plastic zone, and there is a high correlation between the surrounding rock crack range and the plastic zone. The stress characteristics of the surrounding rock in the plastic zone include two main aspects. One is that the direction of the principal stress of the surrounding rock is deflected, which is manifested as an annular distribution of the direction of the maximum principal stress around the roadway. The direction of the minimum principal stress in the upper part of the roadway points to the center of the roadway, and the direction of the minimum principal stress in the lower part of the roadway deviates from the center of the roadway. Second, the ratio of the maximum to minimum principal stress in the surrounding rock is large. Under this stress characteristic, the surrounding rock in the plastic zone has strong shear dilation. The shear dilation makes the crack of the surrounding rock open so that the surrounding rock is squeezed into the roadway space, and then the roadway produces large deformation. Due to the large range of cracks in the butterfly‐shaped plastic zone, the shear dilation deformation produced by the butterfly‐shaped plastic zone is far more than that of the round/oval plastic zone. According to the crack range of roadway surrounding rock under different lateral pressure coefficients, the corresponding support scheme is put forward. Field experiments show that the support scheme can effectively control the deformation of surrounding rock and meet the requirements of roadway use.

Stress–strain Behavior of Silt Sand Soil Under Isotropically Consolidated Drained Conditions by Principal Stress Direction and Intermediate Stress Coefficient Parameters

Stress–strain Behavior of Silt Sand Soil Under Isotropically Consolidated Drained Conditions by Principal Stress Direction and Intermediate Stress Coefficient Parameters

Impact of scan strategy on principal stresses in laser powder bed fusion

Additive manufacturing techniques, such as laser powder bed fusion (PBF-LB), are well known for their exceptional freedom in part design. However, these techniques are also characterized by the development of large thermal gradients during production and thus residual stress (RS) formation in produced parts. In this context, neutron diffraction enables the non-destructive characterization of the bulk RS distribution. By control of the thermal gradients in the powder-bed plane by scan strategy variation we study the impact of in-process scan strategy variations on the microstructure and the three-dimensional distribution of RS. Microstructural analysis by means of electron backscatter diffraction reveals sharp microstructure transitions at the interfaces ranging from 100-200 µm. The components of the RS tensor are determined by means of neutron diffraction and the principal stress directions and magnitudes are determined by eigenvalue decomposition. We find that the distribution of RS in the powder-bed plane corresponds to the underlying scan strategy. When the alternating scan vectors align with the x- and y sample coordinate axes, the principal stress directions co-align. In the present geometry, nearly transverse isotropic stress states develop when the scan vectors are either aligned 45° between x and y or continuously rotated by 67° between each layer.

A modified SWT model for very high cycle fatigue life prediction of L-PBF Ti-6Al-4V alloy based on Single Defect: Effect of building orientation

The ultrasonic fatigue tests on laser-powder bed fused (L-PBF) Ti-6Al-4V specimens manufactured at 0°, 45°, and 90° building orientations were conducted. It is found that the very high cycle fatigue (VHCF) lives decrease with the building orientation from 0°, 45°, to 90°. All the fatigue cracks initiate from internal pores or Lack of Fusion defects. Mode Ι cracks grow perpendicular to the direction of the maximum opening stress, regardless of the building orientation. The maximum prospective defect evaluated by the extreme value statistics (EVS) method is used as the typical defect for VHCF life prediction. A modified Smith-Waston-Topper (SWT) model was proposed and combined with the Critical Distance Method to predict ultra-high cycle fatigue life. The life prediction accuracy was validated by using both experimental data obtained from the experiments conducted in this paper and experimental data taken from the literature. The results show that 84% of the predicted fatigue lives are within a scatter band of 2 standard deviation, and 16% of the predicted lives are outside a scatter band of 2 standard deviation and within a scatter band of 3 standard deviation.

A coupled thermo-mechanical model for investigating cracking and failure of composite interbedded rock

Composite interbedded rock is a special geological phenomenon that occurs when layers of rock (beds) of a given lithology lie between or alternate with other layers of a different lithology. The thermal and mechanical properties of the composite interbedded rocks exhibit strong anisotropy. Studying the thermomechanical coupling properties of natural composite interbedded rocks using existing experimental techniques is challenging. A coupled thermo-mechanical composite interbedded rock model was developed based on Fourier's heat-conduction law and Newton's second law. The thermodynamic responses and biaxial mechanical properties of composite interbedded rocks with different interlayer angles under the coupling of initial stress and thermal loading were studied for the first time. The results indicate that the thermal stresses within the granite interlayers are higher than those within the sandstone interlayers. Throughout the thermal loading process, thermal cracking occurred primarily within the (stiffer) granite interlayers. The number of thermal cracks generated during the cooling process far exceeds that during heating; at 400 °C, the number of thermal cracks during cooling is more than 35 times that during heating. When the interlayer dip angle approaches 90° and is aligned with the major principal stress direction, the phenomenon of the “double peaks” and layered failure becomes more pronounced. Within the range of variables considered, the relative impact of the three variables on peak stress in composite interbedded rock is as follows, from greatest to least: interlayer angle, thermal shock temperature, and model size. The results and developed modeling methods will contribute to the management and optimization of future engineering geology projects.

Numerical simulation of blasting behavior of rock mass with cavity under high in-situ stress

With the shift of coal seam mining to the deep, the in-situ stress of coal and rock mass increases gradually. High ground stress can limit the generation of rock cracks caused by blasting, and blasting usually shows different crushing states than low stress conditions. In order to study the blasting expansion rule of rock mass with cavity under high ground stress and the rock mass fracture state under different side stress coefficients. In this paper, the effective range of blasting and the stress distribution under blasting load are analyzed theoretically. The RHT (Riedel-Hiermaier-Thoma) model is used to numerically simulate the blasting process of rock mass with cavity under different ground stress, and the influence of ground stress and lateral pressure coefficient on the crack growth of rock mass is studied. The results show that when there is no ground stress, the damage cracks in rock mass are more concentrated in the horizontal direction and the fracture development tends to the direction where the holes are located, which confirms the guiding effect and stress concentration effect of the holes in rock mass, which helps to promote the crack penetration between the hole and the hole. The length difference of horizontal and vertical damage cracks in rock mass increases with the increase of horizontal and vertical stress difference. Under the same lateral stress coefficient, the larger the horizontal and vertical stress difference is, the stronger the inhibition effect on crack formation is. For blasting of rock mass with high ground stress, the crack formation length between gun holes decreases with the increase of stress level, and the crack extends preferentially in the direction of higher stress. Therefore, the placement of gun holes along the direction of greater stress and the shortening of hole spacing are conducive to the penetration of cracks between gun holes and empty holes. The research can provide reference for rock breaking behavior of deep rock mass blasting.

A transient radial cortical microtubule array primes cell division in Arabidopsis

Although the formation of new walls during plant cell division tends to follow maximal tensile stress direction, analyses of individual cells over time reveal a much more variable behavior. The origin of such variability as well as the exact role of interphasic microtubule behavior before cell division have remained mysterious so far. To approach this question, we took advantage of the Arabidopsis stem, where the tensile stress pattern is both highly anisotropic and stable. Although cortical microtubules (CMTs) generally align with maximal tensile stress, we detected a specific time window, ca. 3 h before cell division, where cells form a radial pattern of CMTs. This microtubule array organization preceded preprophase band (PPB) formation, a transient CMT array predicting the position of the future division plane. It was observed under different growth conditions and was not related to cell geometry or polar auxin transport. Interestingly, this cortical radial pattern correlated with the well-documented increase of cytoplasmic microtubule accumulation before cell division. This radial organization was prolonged in cells of the trm678 mutant, where CMTs are unable to form a PPB. Whereas division plane orientation in trm678 is noisier, we found that cell division symmetry was in contrast less variable between daughter cells. We propose that this "radial step" reflects a trade-off in robustness for two essential cell division attributes: symmetry and orientation. This involves a "reset" stage in G2, where an increased cytoplasmic microtubule accumulation transiently disrupts CMT alignment with tissue stress.