Dynamic Peak Strain Research Articles

Experimental Study on Dynamic Mechanical Properties and Energy Evolution Characteristics of Limestone Specimens Subjected to High Temperature

To study the effect of high temperature on the dynamic mechanical properties and energy evolution characteristic of limestone specimens, the basic physical parameters of limestone specimens that cool naturally after experiencing high temperatures of room temperature (25°C), 200°C, 400°C, and 600°C were tested. In addition, compression tests with 6 impact loading conditions were conducted using SHPB device. The changes of basic physical properties of limestone before and after temperature were analyzed, and the relationship among dynamic characteristic parameters, energy evolution characteristics, and temperature was discussed. Test results indicated that, with the increase of temperature, the surface color of specimen changed from gray‐black to gray‐white, and its volume increased, while the mass, density, and P‐wave velocity of specimen decreased. The dynamic compressive stress‐strain curve of limestone specimens after different high‐temperature effects could be divided into three stages: elasticity stage, yield stage, and failure stage. Failure mode of specimen was in the form of spalling axial splitting, and the degree of fragmentation increased with the increase of the temperature and incident energy. With the increase of the temperature, the reflection energy, the absorption energy, the dynamic compressive strength, and dynamic elastic modulus of rock decreased, while its transmission energy, the dynamic peak strain, and strain rate increased. The dynamic compressive strength, dynamic elastic modulus, dynamic strain, and strain rate of limestone specimens all increased with the increase of incident energy, showing a quadratic function relationship.

Impact Properties of Recycled Aggregate Concrete with Nanosilica Modification

The optimal soaking time and nanosilica concentration were chosen by the physical properties of the nanosilica‐modified recycled aggregate. Recycled aggregate concrete (RAC) and nanosilica recycled aggregate concrete (SRAC) were fabricated by using ordinary recycled aggregate and nanosilica‐modified recycled aggregate. Based on the comparative experimental study of basic mechanical properties, the effects of nanosilica recycled aggregate(SRA) modification and recycled aggregate(RA) replacement percentage on the basic mechanical properties of recycled concrete were analyzed. Finally, the split‐Hopkinson pressure bar (SHPB) was used to conduct comparative experimental research on the impact resistance of recycled aggregate concrete and nanosilica‐modified recycled aggregate concrete. The effects of nanosilica recycled aggregate modification and aggregate replacement percentage on failure morphology, dynamic peak stress, dynamic increase factor (DIF), dynamic peak strain were analyzed.

Investigation on the Effects of Prefabricated Crack and Strain Rate on Uniaxial Compressive Properties of Frozen Silty Soil

To investigate the uniaxial compressive strength and deformation properties of frozen silty soil with prefabricated crack under various strain rates, the static uniaxial compressive tests were conducted for frozen silty soil using three kinds of binder materials to select the suitable prefabricated crack manufacturing method. Afterward, the static and dynamic stress‐strain curves of frozen silty soil with different prefabricated crack numbers were obtained based on static and splitting Hopkinson pressure bar (SHPB) tests. In addition, the high‐speed camera was employed to record the fracturing process of frozen silty soil under impact loads. Results indicated that the frozen silty soil specimens with no binder showed higher static strength compared with other two binder materials (plaster and Vaseline). The strength growth rate of frozen silty soil showed three‐stage (fast‐slow‐rapid) change characteristics. The peak strain of frozen silty soil under static loads scope was higher compared with that under dynamic loads, while its dynamic peak strain with various prefabricated crack numbers was remarkably rate‐dependent. The absorbed energy density of frozen silty soil was subject to a negative (positive) relationship with the prefabricated crack numbers (strain rate). The dominated crack of intact frozen silty soil specimen finally presented Y‐shaped shear failure. However, tensile cracks parallel to stress wave propagation direction were observed for the frozen silty soil specimen with prefabricated crack.

Dynamic mechanical properties of cementitious composites with carbon nanotubes

This paper studied the effect of different types of multi-walled carbon nanotubes (MWCNTs) on the dynamic mechanical properties of cementitious composites. Impact compression test was conducted on various specimens to obtain the dynamic stress-strain curves and dynamic compressive strength as well as deformation of cementitious composites. The dynamic impact toughness and impact dissipation energy were, then, estimated. Furthermore, the microscopic morphology of cementitious composites was identified by using the scanning electron microscope to show the reinforcing mechanisms of MWCNTs on cementitious composites. Experimental results show that all types of MWCNTs can increase the dynamic compressive strength and ultimate strain of the composite, but the dynamic peak strain of the composite presents deviations with the MWCNT incorporation. The composite with thick-short MWCNTs has a 100.8% increase in the impact toughness, and the composite with thin-long MWCNTs presents an increased dissipation energy up to 93.8%. MWCNTs with special structure or coating treatment have higher reinforcing effect to strength of the composite against untreated MWCNTs. The modifying mechanisms of MWCNTs on cementitious composite are mainly attributed to their nucleation and bridging effects, which prevent the micro-crack generation and delay the macro-crack propagation through increasing the energy consumption.

Dynamic mechanical characteristics and failure mode of serpentine under a three-dimensional high static load and frequent dynamic disturbance.

The improved split Hopkinson pressure bar (SHPB) was used to study the dynamic mechanical properties and failure characteristics of surrounding rock in deep rock mass engineering that is under high stress and affected by blasting excavation and other dynamic disturbances. In a three-dimensional high static load and frequent dynamic disturbance test, the preload high axial pressure and confining pressure are used to simulate the high crustal stress of deep rock, and the effect of small disturbances on the rock is simulated by the low impact load. The results show that there are two types of dynamic stress-strain curves of deep rock: an elastic-plastic curve and plastic-elastic-plastic curve. The curves consists of five parts: the compaction stage, micro-crack steady development stage, micro-crack unstable propagation stage, fatigue damage stage, and fatigue failure stage. Reductive phenomena of constringent strain after dynamic peak stress appear because of the different degrees of rock damage. Moreover, these phenomena include two conditions, namely, whether rebound occurs or not. The impact resistance of rock is strongest when the ratio of the confining pressure to axial pressure is optimal, and the dynamic average strength of rock and accumulative impact times decrease with the increase of the preloaded axial compression and increase with the increase of the preloaded confining pressure. Both the dynamic deformation modulus and dynamic peak stress decrease with the increase of the accumulative impact time, while the maximum strain and the dynamic peak strain increase. The corresponding rebound strain as a whole first increases and then decreases with the increasing impact times. For deep rock, tensile failure and single-bevel plane shear failure are the main failure modes, and pull-compression mixed friction failure is the auxiliary failure mode. Additionally, the lumpiness of broken rock decreases with the increase of the preloaded axial compression and increases with the increase of the preloaded confining pressure.

Static-dynamic strain response to the 2016 M6.2 Hutubi earthquake (eastern Tien Shan, NW China) recorded in a borehole strainmeter network

The 2016 M6.2 Hutubi Earthquake is an event occurred on a reverse fault located in the northern Chinese Tien Shan, but it is debatable whether the seismogenic fault is a low-angle thrust fault. The coseismic strain responses have been recorded by nine 4-component RZB borehole strainmeters, locating 11–320 km away from the epicenter. The nearest four stations have recorded resolvable static strain responses. The authors used the theoretic tide to calibrate the strains, and relocated the 10.31 km by 6.85 km fault plane through a grid-search method. Two groups of fault parameters 279°/70°/87° and 103°/28°/85° were obtained, and the predictions for 24/26 channels for both groups are consistent with the offsets observed in the near stations by correcting the azimuths. The seismogenic fault is more likely the high-angle backthrust fault based on the comparison with the selected aftershocks. Furthermore, all strainmeters have recorded the dynamic strain waves. The dynamic strains are sensitive to the seismic wave propagation direction, and the peak dynamic strains decay faster in the N-S direction than that in the E-W direction due to the regional structure features. The absolute static strains are comparable to the dynamic strains in the near field, but the ratios between them decrease remarkably in the intermediate and far field. The difference in the dependence on distance was found to be useful to differentiate static strains from dynamic strains.

Coseismic changes in subsurface structure associated with the 2018 Hokkaido Eastern Iburi Earthquake detected using autocorrelation analysis of ambient seismic noise

Autocorrelation analysis using ambient noise is a useful method to detect temporal changes in wave velocity and scattering property. In this study, we investigated the temporal changes in seismic wave velocity and scattering property in the focal region of the 2018 Hokkaido Eastern Iburi Earthquake. The autocorrelation function (ACF) was calculated by processing with bandpass filters to enhance 1–2 Hz frequency range, with aftershock removal, and applying the one-bit correlation technique. The stretching method was used to detect the seismic wave velocity change. After the mainshock, seismic velocity reductions were observed at many stations. At N.AMAH and ATSUMA, which are located close to the mainshock, we detected 2–3% decreases in seismic wave velocity. We compared parameters indicating strong ground motion and showed the possibility of correlations with peak dynamic strain and seismic velocity reduction. We also investigated the relationship between waveform correlation and lag time, using ACFs from before and after the mainshock, and detected distortion of the ACF waveform. The source of the waveform decorrelation was estimated to be located near the maximum coseismic slip, at around 30 km depth. Thus, distortion of the ACF waveform may reflect the formation of cracks, due to faulting at approximately 30 km depth.

Monitoring the Dynamic Response of a Buried Polyethylene Pipe to a Blast Wave: An Experimental Study

Although the use of polyethylene (PE) pipelines has become increasingly widespread in recent years, few studies have addressed their seismic design and ability to withstand blast waves. In order to establish their seismic capacity, the dynamic response of buried pipelines subjected to blast waves must be explored in depth. Here, we studied the dynamic response of PE pipes situated near an explosive source. Time histories of dynamic strains were measured by conventional strain gauges after simple waterproof treatment, and pipe and ground vibration velocity curves were obtained. Based on the experimental data, the attenuation law of the peak strains under the conditions of different charge masses and blast center distances was analyzed, and the spectrum characteristics of strain, velocity of the pipe, and ground velocity were studied. The results revealed that a large hoop strain on the PE pipes was produced due to the local impact near the explosive source. We found that peak hoop strain (PHS) or peak axial strain (PAS) had a power attenuation relationship with the scaled distance, and this relationship could also be derived by dimensional analysis. The average frequency of strains had the same attenuation form as the charge mass, which was between 10 Hz and 50 Hz. Additionally, the vibration of the pipe showed a low frequency. We also determined that the attenuation of the average frequency of pipe and ground vibration velocity was closely related to the charge mass and the scaled distance. Pipe peak vibration velocity (PPVV), ground peak particle velocity (GPPV), and the peak dynamic strain of pipe were highly positively correlated, which verifies the feasibility of using GPPV to characterize pipeline vibration and strain level. Thus, a blasting criterion of 10% minimum request strength (MRS) for PE pipe was proposed, which means that the additional PHS or PAS of the dangerous point must be less than 10% MRS, and we also propose limiting the safety distance–charge mass for blasts near buried PE pipelines by the criterion. Some results in this paper can serve as the basis for future in-depth theoretical research.

Dynamic impact behaviors and constitutive model of super-fine stainless wire reinforced reactive powder concrete

The dynamic impact behavior of super-fine stainless wire (SSW) reinforced reactive powder concrete (RPC) was studied through split hopkinson pressure bar test with the strain rate range from 94/s to 926/s in this paper. The modification mechanisms of SSW to the dynamic impact performance of RPC were revealed via computed tomography and scanning electron microscope analysis. Experimental results showed that the dynamic impact compressive strength of SSW reinforced RPC increases with the strain rate. The dynamic increase factor of compressive strength is decreased and the strain-rate strengthening effect of RPC is weakened by SSW. The maximum dynamic peak strain of SSW reinforced RPC reaches up to 34,070 µε at the strain rate of 305/s. The limit strain of RPC is decreased because of the lateral confinement effect of SSW. The stress-strain curves of SSW reinforced RPC include elastic stage, elastic-plastic stage and descending stage. The addition of SSW leads 43.5% and 58.2% of increase in dynamic impact toughness and impact dissipate energy of RPC, respectively. Increasing SSW volume fraction makes more SSW to inhibit the generation and propagation of cracks in RPC, thus leading to the decrease of destruction degree. The formation of inter-anchored interface among bundling SSW increases the resistance of RPC to crack development. The dynamic impact constitutive model established on the basis of revised visco-elastic and damage theory can well describe the stress-strain relationship of SSW reinforced RPC at different strain rates, in which the strain threshold is governed by strain rate and SSW volume fraction simultaneously.

The Effect of High Loading Rate on the Behaviour and Mechanical Properties of Coal‐Rock Combined Body

In order to investigate the high loading rate effect on the behaviour and mechanical properties of coal‐rock combined body, the dynamic compressive tests were conducted by using the Split‐Hopkinson Pressure Bar (SHPB) device under the loading rate range from 2.7×105 MPa/s to 4.0×105 MPa/s. The stress‐strain curves, dynamic peak stress and strain, elastic modulus, and energy distribution law of coal‐rock combined body under different loading rates were analyzed and discussed. The results show that the dynamic stress‐strain curves of coal‐rock combined body have a double‐peak feature under high loading rate range, which can be divided into the initial bearing stage, the bearing decline stage, the bearing enhance stage, and the unstable stage. The first peak stress of the coal‐rock combined body is independent of the loading rate, while the dynamic compressive strength (the second peak stress) and dynamic peak strain (the second peak strain) have a strong loading rate effect and will generally increase linearly with the loading rate. The first and second elastic moduli of coal‐rock combined body are not sensitive to the loading rate. With the increase of the loading rate, the incident energy and reflective energy of coal‐rock combined body increase rapidly, while the change of transmitted energy is very small. The absorption energy ratio of the coal‐rock combined body shows a good linear law with the incident energy under different loading rates.

An experimental study: Integration device of Fiber Bragg grating and reinforced concrete beam for measuring debris flow impact force

The impact effect of boulder within debris flow is the key factor contributing to peak impact as well as to the failure of debris flow control work. So accurate measuring and calculating the impact force of debris flow can ensure the engineering design strength. However, limited to the existing laboratory conditions and piezoelectric sensor performance, it is impossible, based on the conventional measurements, to devise a computing method for expressing a reliable boulder impact force. This paper has therefore designed a new measurement device according to the method of integrating Fiber Bragg grating (FBG) and reinforced concrete composite beam (RCB) for measuring the impact force of debris flows, i.e. mounting FBG on the axially stressed steel bar in the composite beam at regular intervals to monitor the steel strain. RCB plays the role of contacting debris flow and protecting FBG sensors. Taking this new device as the experimental object, drop testing is designed for simulating and reflecting the boulder impact force. In a series of impacting tests, the relationship between the peak dynamic strain value of the steel bar and the impact force is analyzed, and based on which, an inversion model that uses the steel bar strain as the independent variable is established for calculating the boulder impact force. The experimental results show that this new inversion model can determine the impact force value and its acting position with a system error of 18.1%, which can provide an experimental foundation for measuring the impact force of boulders within the debris flow by the new FBG-based device.

Aluminum and E-glass epoxy plates behavior subjected to shock loading

The terrorist attacks and dangers by bomb blast have turned into an emerging issue throughout the world and the protection of the people and structures against terrorist acts depends on the prediction of the response of structures under blast and shock load. In this paper, behavior of aluminum and unidirectionally reinforced E-Glass Epoxy composite plates with and without focal circular holes subjected to shock loading has been identified. For isotropic and orthotropic plates (with and without holes) the classical normal mode approach has been utilized as a part of the processing of theoretical results. To obtain the accurate results, convergence of the results was considered and a number of modes were selected for plate with and without hole individually. Using a shock tube as a loading device, tests have been conducted to composite plates to verify the theoretical results. Moreover, peak dynamic strains, investigated by experiments are also compared with the theoretical values and deviation of the results are discussed accordingly. The strain-time histories are likewise indicated for a specific gauge area for aluminum and composite plates. Comparison of dynamic-amplification factors between the isotropic and the orthotropic plates with and without hole has been discussed.

Evidence for Static and Dynamic Triggering of Seismicity Following the 24 August 2016, M W = 6.0, Amatrice (Central Italy) Earthquake

The recent 24 August 2016, MW = 6.0, Amatrice earthquake (central Italy) and the resulting aftershock sequence represents a test case to investigate the static and dynamic stress/strain contribution to the triggering of the sequence. Here we test the hypothesis that either static or dynamic stress contribution alone may not be sufficient to explain the aftershock distribution. We first inferred the horizontal source rupture directivity together with an estimate of the surface fault projection from the analysis of the peak-ground velocity. We computed the peak-dynamic strain field, modified by source directivity, using the peak-ground velocity as a strain proxy and the Coulomb static stress change. Finally, we compared the seismicity rate map (β-statistic) with each of the estimated fields to investigate correlations with the aftershock pattern. We found that the area of the highest values of the estimated peak-dynamic strain field better reproduces the observed asymmetry in the aftershock distribution. This suggests that, in addition to Coulomb static stress change, dynamic strain enhanced by source directivity, contributed to the triggering of the Amatrice earthquake aftershocks.

Investigating Triggering of the Aftershocks of the 2014 Napa Earthquake

Abstract The occurrence of the M w 6.0 South Napa California earthquake, on 24 August 2014 at 03:20 a.m. local time, triggered discussion in the seismological community about the level of damage associated with such a moderate‐magnitude event and about the geometry and orientation of the causative fault. In addition, coulomb static stress change mapping does not seem to be able to fully explain near‐source aftershock distribution. Here, we find clear evidence of a north‐northwest source directivity from the analysis of the spatial distribution of peak ground motion. The area of the highest values of the estimated peak dynamic strain field, computed accounting for fault extent and source directivity, agrees with the near‐source aftershock distribution. This might suggest that, in addition to coulomb static stress change, dynamic strain also contributed to the triggering of near‐source Napa earthquake aftershocks. The approach used here might be useful to identify areas likely prone to aftershock occurrence.

Effects of Thermal Treatment on the Dynamic Mechanical Properties of Coal Measures Sandstone

Many projects such as the underground gasification of coal seams and coal-bed methane mining (exploitation) widely involve the dynamic problems of coal measures sandstone achieved via thermal treatment. This study examines the dynamic mechanical properties of coal measures sandstone after thermal treatment by means of an MTS653 high-temperature furnace and Split Hopkinson pressure bar test system. Experimental results indicate that 500 °C is a transition point for the dynamic mechanical parameters of coal measures sandstone. The dynamic elastic modulus and peak strength increase linearly from 25 to 500 °C while the dynamic peak strain decreases linearly over the same temperature range. The dynamic elastic modulus and peak strength drop quickly from 500 to 800 °C, with a significant increase in the dynamic peak strain over the same temperature range. The rock mechanics are closely linked to material composition and mesoscopic structure. Analysis by X-ray diffraction and scanning electron microscopy indicate that the molecules inside the sandstone increase in density due to the thermal expansion of the material particles, which effectively improves the deformation resistance and carrying capacity of the sandstone and reduces the likelihood of axial deformation. With heat treatment that exceeds 500 °C, the dynamic mechanical properties rapidly weaken due to the decomposition of kaolinite; additionally, hot cracking of the mineral particles within the materials arises from coal sandstone internal porosity, and other defects gradually appear.

Mechanical properties of ceramics–cement based porous material under impact loading

Cementitious materials and ceramic aggregates used as basic materials, ceramics–cement based porous material (CCPM) has been prepared. Φ100mm SHPB has been improved by wave shaping techniques, which can guarantee the availability of the tests. Quasi static compression test and impacting compression test have been carried out, the damage process of specimen under loading has been analyzed, and mechanics parameters under different strain rates have been obtained, moreover, based on this, the mechanical properties of CCPM under impact loading, including strength property, deformation property, impacting toughness, have been studied, in addition, the prospect of CCPM’s application has also been discussed. The results indicate that, the quasi static and impact compressive stress–strain curve of CCPM includes a strain plateau, which helps to better absorb energy; the dynamic strength increase factors of CCPM and the natural logarithm of relative strain rate are of a linear relationship; the relationship between the dynamic peak strain increase factors and the related strain rate can be described with an exponential linear, which shows obvious “damage softening” effect; with the increase of average strain rate, the impacting toughness of CCPM gets strengthened continuously and the impact toughness indexes are in a logarithm relationship with strain rate; CCPM is more strain rate sensitive than ordinary cement based composite materials. Thus it can be seen, CCPM possesses the advantageous mechanical properties of both porous materials and ordinary cement based composite materials. Besides, the material is easy to prepare and simple to make. Along with its high plasticity and low density, CCPM has a promising future to perform its potential advantages in engineering, especially in national defense engineering.

Effects of strain waveform on low cycle fatigue behaviour of near α Timetal 834 titanium alloy

The low cycle fatigue (LCF) behaviour of a near α Timetal 834 titanium alloy has been studied under fast–slow and slow–fast waveforms at peak dynamic strain aging (DSA) temperature (450 °C). The alloy exhibits inferior fatigue life under slow–fast waveform as compared to fast–slow waveform. This is attributed to slow rate of straining in tensile direction under slow–fast waveform which allows more interaction between mobile dislocations with solute atoms thereby enhancing the strength of DSA. A life prediction model based on the dynamic viscosity with waiting time correction as per dislocation kinetics predicts fatigue lives reasonably well under pronounced DSA effect.

Connecting near‐field and far‐field earthquake triggering to dynamic strain

Any earthquake can trigger more earthquakes. This triggering occurs in both the classical aftershock zone as well as the far field. These populations of triggered earthquakes may or may not be distinct in terms of triggering mechanism. Here we look for a distinction between the populations by examining how the observed intensity of triggering scales with the amplitude of the triggering strain in each. To do so, we apply a new statistical metric based on earthquake interevent times to a large data set and measure earthquake triggering as a function of dynamic strain amplitude, where strain is estimated from empirical ground motion regressions. This method allows us to identify triggering at dynamic strain amplitudes down to 3 × 10−9, orders of magnitude smaller than previously reported. This threshold appears to be an observational limit and shows that extremely small dynamic strains can trigger faults that are sufficiently near failure. Using a probabilistic model to transform measured interevent times to seismicity rate changes, we find that triggering rates in the far field scale with peak dynamic strain. This scaling, projected into the near field, accounts for 15%–60% of earthquakes within 6 km of magnitude 3–5.5 earthquakes. Statistical seismicity simulations validate the interevent time method and show that the data are consistent with the number of far‐field triggered earthquakes being linearly proportional to peak dynamic strain. We interpret the additional near‐field component as reflecting either static stress triggering, more effective dynamic triggering at higher frequencies, or a concentration of aftershock nucleation sites very near main shocks.

Earthquake triggering of mud volcanoes

Mud volcanoes sometimes erupt within days after nearby earthquakes. The number of such nearly coincident events is larger than would be expected by chance and the eruptions are thus assumed to be triggered by earthquakes. Here we compile observations of the response of mud volcanoes and other geologic systems (earthquakes, volcanoes, liquefaction, ground water, and geysers) to earthquakes. The compilation shows a clear magnitude–distance threshold for triggering, suggesting that these seemingly disparate phenomena may share similar underlying triggering mechanisms. The compilation also shows that pre-existing geysers and already-erupting volcanoes and mud volcanoes are much more sensitive to earthquakes than quiescent systems. Several changes produced by earthquakes have been proposed as triggering mechanisms, including liquefaction and loss of strength, increased hydraulic permeability or removing hydraulic barriers, and bubble nucleation and growth. We present new measurements of the response of erupted mud samples to oscillatory shear at seismic frequencies and amplitudes, and find that loss of strength occurs at strain amplitudes greater than 10 −3. This is much larger than the peak dynamic strains associated with earthquakes that may have triggered eruptions or influenced already-erupting mud volcanoes. Therefore, we do not favor loss of strength as a general triggering mechanism. Mechanisms involving bubbles require significant supersaturation or incompressible mud, and neither condition is likely to be relevant. We analyze the response of the Niikappu group of mud volcanoes in Japan to several earthquakes. We find that this system is insensitive to earthquakes if an eruption has occurred within the previous couple of years, and that static strain magnitudes are very small and not correlated with triggering suggesting that triggering likely results from dynamic strain. Moreover, triggering may be frequency-dependent with longer period seismic waves being more effective at triggering. Available data are insufficient, however, to determine whether triggering characteristics at Niikappu are representative of triggered eruptions in general. Nor can we determine the exact mechanism by which dynamic (long-period) strains induce eruption, but given the apparent failure of all mechanisms except increasing permeability and breaching barriers we favor these. More observations and longer records are needed. In particular, gas measurements and broadband seismic data can be collected remotely and continuously, and provide key information about processes that occur during and immediately after the arrival of seismic waves.

Growth rate rather than gender determines the size of the adaptive response of the growing skeleton to mechanical strain

To determine whether male and female skeletons are equally responsive to mechanical load, the left ulnae in a group of juvenile male (n = 7), and age-matched female (n = 9) rats received a short daily period of controlled dynamic loading in vivo (1200 cycles at 2 Hz each day for 10 days) in addition to their normal exercise. Axial loads for each group were adjusted to engender a peak dynamic strain of −4000 microstrain at the medial face of the ulna midshaft, applied and released at a rate of ±30,000 microstrain/sec. Fluorescent labels were administered at the start and finish of the loading period. Over the course of daily loading, the body mass of the male rats increased 2.5 times faster than that of the females (6.3 g/day vs. 2.5 g/day). The increase in periosteal interlabel bone area due to growth and normal exercise was also 2.5 times greater in the males than in the females. Both genders showed statistically significant (p < 0.05) increases in periosteal new bone deposition in the ulna of their loaded compared with their control limb. The pattern of osteogenic response was similar in males and females and featured increased mineral apposition rate on the lateral surface of the ulna, and arrest of modeling-drift-related resorption with its reversal to bone formation on the medial surface. In males, the absolute loading-related increase in bone area was six times greater than that in females. However, when the absolute size of the loading-related change in periosteal interlabel new bone deposition was expressed relative to that due to growth, there was no difference between males and females (Mean ± SEM: 37 ± 12% for males, 34 ± 12% for females). These data confirm that the ulna of young actively growing rats of both genders responds to a short daily period of loading with an altered modeling response that involves increased bone formation and decreased resorption. Although the absolute amount of new bone formation stimulated by loading is greater in males than in females there is no difference between genders following correction for the higher rate of bone deposition seen in the males in association with their faster rate of growth.