Impact Deformation Research Articles

Effect of Dual Shot Peening on Microstructure and Wear Performance of CNT/Al-Cu-Mg Composites.

This work systematically investigated the effect of dual shot peening (DSP) and conventional shot peening (CSP) on the microstructure, residual stress and wear performance of the CNT/Al-Cu-Mg composites. The results indicated that compared with CSP, DSP effectively reduced surface roughness (Rz) from 31.30 to 12.04 μm. In parallel, DSP introduced a smaller domain size (33.1 nm) and more dislocations, higher levels compressive residual stress and a stiffer deformation layer with deeper affected zones. Moreover, DSP effectively improved the uniformity of the surface layer's microstructure and residual stress distribution. The improvement is mainly due to secondary impact deformation by microshots and fine grain strengthening. In addition, the transformation of the hard second phases such as Al4C3 and CNT and its effects on improving the surface strength and deformation uniformity were discussed. Significantly, DSP improved the wear resistance by 31.8% under the load of 6 N, which is attributed to the synergistic influence of factors including hardness, compressive residual stress, surface roughness, and grain size. In summary, it can be concluded that DSP is an effective strategy to promote the surface layer characteristics for CNT/Al-Cu-Mg composites.

Experimental study on multiple self-healing and impact properties of 2D carbon fiber fabric-reinforced epoxy composites with shape memory properties

Fiber-reinforced thermoset polymers are widely used in aerospace as a material with excellent performance. However, for the low-velocity impact damage to which they are most susceptible, existing repair methods are difficult to maintain the aerodynamic performance of the components (back to its pre-damage shape) after repair. In this study, the multiple impact deformation recovery, internal damage healing, and post-repair impact properties of epoxy-PCL (ε-caprolactone) 2D carbon fiber fabric-reinforced polymers with shape memory and self-healing properties were investigated. The material is manufactured using a hot press tank-prepreg process, curing at 160 degrees for 3.5 hours at 6 atmospheres. The results show that the incorporation of thermoplastic PCL into the composite matrix can enhance the self-healing ability and impact resistance of the material. Composites after lower energy impacts retain their structural integrity and mechanical properties after healing. Materials can recover effectively from a single impact, but repeated impacts can lead to more extensive damage, which makes healing more difficult and causes a decrease in Healing efficiency. The shape memory effect of composites can restore plastic deformation caused by impact, which highlights the potential of shape memory smart composites for aerospace applications.

Low-velocity impact response and damage mechanism of cosine function cell-based lattice core sandwich panels

This study aims to investigate the impact response and damage mechanism of cosine-function cell-based (CFCB) lattice core sandwich panels. Several low-velocity impact tests were conducted to explore their advantages in impact resistance by comparing them with traditional body-centered cubic (BCC) lattice-core sandwich panels. The impact response and deformation patterns of CFCB lattice core sandwich panels with two different faceplate materials (aluminum alloy and carbon fiber reinforced plastic composite) were experimentally investigated. The CFCB lattice core sandwich panels exhibited higher impact resistance and energy absorption capacity than their BCC lattice core counterparts. Furthermore, sandwich panels with aluminum alloy faceplates provided better impact resistance capacity than those with CFRP faceplates. Subsequently, several numerical models were developed to explore the deformation mechanisms and energy absorption characteristics of CFCB lattice core sandwich panels. In addition, the effects of the core structural parameters on mechanical performance were numerically investigated. Results indicated that increasing the cell rod diameter and/or reducing the cosine period length could decrease the indentation depth and enhance crush force efficiency. Finally, based on the principle of minimum potential energy, a theoretical model was developed to predict the initial peak load of CFCB lattice core sandwich panels with isotropic faceplates. This study aimed to explore the impact response and provide design guidance for CFCB lattice core sandwich panels.

Study on the room temperature compression deformation mechanism and microstructural evolution of Mg-Gd-Y-Zr alloy

This study explores the dynamic impact deformation mechanisms of Mg-Gd-Y-Zr alloys, specifically focusing on the influence of varying Gd content. Using metallographic observation, SEM, EDS, XRD, EBSD, and TEM, along with hardness and room-temperature compression tests, the research investigates the effects of Gd content on the microstructure, mechanical properties, and deformation behaviors of as-cast Mg-(x)Gd-3Y-0.5Zr (x = 6.5/7.5/8.5) alloys.The results show that increasing Gd content reduces grain size and increases the volume fraction of the non-equilibrium eutectic phase Mg24(Gd,Y)5, though with smaller phase dimensions. These alloys exhibit excellent compressive properties at room temperature, with the highest compression deformation rate of 27.8 % observed at 6.5 % Gd and the maximum compressive strength of 401 MPa recorded at 8.5 % Gd, surpassing some high-Gd-content cast and extruded alloys.At lower Gd content, basal slip and tensile twinning are the primary deformation mechanisms. As Gd content increases, these mechanisms evolve to include prismatic slip and compressive twinning. The fracture mode transitions from predominantly ductile to a combination of ductile and brittle features, with an increase in brittle cleavage at higher Gd levels.

Unveiling mechanical response and deformation mechanism of extruded WE43 magnesium alloy under high-speed impact

To clarify the mechanical behavior and deformation mechanism of rare earth magnesium (Mg) alloy WE43 under extreme service loads, high-speed impact tests under various deformation temperatures and loading paths were conducted using a split Hopkinson pressure bar. The flow stress along extrusion direction (ED) and extrusion radial direction (ERD) decreases apparently with deformation temperature. Compared with conventional Mg alloys, it exhibits a slight anisotropy and an unusual C-shaped characteristic. Cellular dislocation, mechanical twin and fine grain that occur after high-speed impact deformation are insensitive to the loading direction, but strongly dependent on the deformation temperature, especially superimposed with adiabatic temperature rise. As a result, dynamic recrystallization (DRX) occurs even at an ambient temperature of 25 °C. Double twinning and prismatic slip or pyramidal slip are the dominant deformation mechanisms at 25 °C. These twins induce mechanical cutting refinement to form some fine-grained structures, accompanied by a small number of fine grains by twinning induced DRX. In contrast, the deformation at 250 °C is mainly controlled by prismatic slip and pyramidal slip, accompanied by various types of twinning in early deformation stage. Compared with 25 °C, more fine-grained microstructures are formed at 150 and 250 °C through a synergy mechanism of twinning induced mechanical cutting and twinning induced DRX.

Temperature Effect on Deformation Mechanisms and Mechanical Properties of Welded High-Mn Steels for Cryogenic Applications.

High-manganese steel (high-Mn) is valuable for its excellent mechanical properties in cryogenic environments, making it essential to understand its deformation behavior at extremely low temperatures. The deformation behavior of high-Mn steels at extremely low temperatures depends on the stacking fault energy (SFE) that can lead to the formation of deformation twins or transform to ε-martensite or α'-martensite as the temperature decreases. In this study, submerged arc welding (SAW) was applied to fabricate thick pipes for cryogenic industry applications, but it may cause problems such as an uneven distribution of manganese (Mn) and a large weldment. To address these issues, post-weld heat treatment (PWHT) is performed to achieve a homogeneous microstructure, enhance mechanical properties, and reduce residual stress. It was found that the difference in Mn content between the dendrite and interdendritic regions was reduced after PWHT, and the SFE was calculated. At cryogenic temperatures, the SFE decreased below 20 mJ/m2, indicating the martensitic transformation region. Furthermore, an examination of the deformation behavior of welded high-Mn steels was conducted. This study revealed that the tensile deformed, as-welded specimens exhibited ε and α'-martensite transformations at cryogenic temperatures. However, the heat-treated specimens did not undergo α'-martensite transformations. Moreover, regardless of whether the specimens were subjected to Charpy impact deformation before or after heat treatment, ε and α'-martensite transformations did not occur.

Axial Impact Performances of Composite Aluminum Foam Tubes

An improved melt foaming method is employed to fabricate composite aluminum foam tubes (CAFTs) with varying diameter ratios, achieving metallurgical bonding between the aluminum foam and aluminum tubes. Based on the structural characteristics of aluminum foam‐filled tubes and traditional numerical formula for calculating the energy absorption properties of metal foams, a new calculation formula is proposed to accurately evaluate energy absorption performance of CAFTs under axial load, enabling more precise numerical calculation of total energy absorption. Furthermore, drop weight impact tests and finite element simulations are conducted to investigate the axial impact performance and deformation mechanism of CAFTs. The influence of diameter ratio on crashworthiness and energy absorption performance is also analyzed. As the diameter ratios decrease, both the impact resistance and total energy absorption of CAFTs increase, while the degree of tube damage gradually decreases. Moreover, finite element simulation results demonstrate that metallurgical combination between aluminum foam and aluminum tubes effectively transfers stress to thin‐walled tubes with better load‐bearing performance, preventing concentrated collapse of aluminum foam core. Additionally, the presence of aluminum foam provides robust restraint against deformation or rupture in thin‐walled tubes.

Grain misorientation induced low-temperature impact toughness deterioration and its deformation mechanism of Ti6321 titanium alloy

In this study, the impact toughness and deformation mechanism of base metal (BM), heat affected zone (HAZ) and weld zone (WZ) of Ti6321 alloy joint at different temperatures (20 °C, 0 °C, −20 °C, −40 °C, −60 °C and −196 °C) are studied. The microstructure of BM consists of primary α (αp), acicular α and β phase. The HAZ is composed of αp, acicular α, acicular martensite (α′) and β phase. The WZ is composed of acicular α′, lath α′ and β phase. All the BM, HAZ and WZ obtain the highest impact toughness at 20 °C, which are 51 J, 75 J and 72 J, respectively. Under −196 °C, brittle fractures occurs in the BM, HAZ and WZ, and their impact toughness are 18 J, 22 J and 30 J, respectively. Compared with the impact test at −196 °C, the fracture surface of 20 °C by impact test has higher kernel average misorientation and geometrically necessary dislocation. The fracture impact resistance at 20 °C is greater. Grain deformation at 20 °C consumes more energy and the crack propagation path is more tortuous.

Research of the properties of the sandwich-structured Ni60CuMo self-lubricating coating with stepped hardness distribution on Vermicular cast iron by laser cladding

To enhance the wear resistance of Vermicular cast iron (RuT300) and achieve the stepped hardness distribution for the impact deformation resistance in the middle and lower part of the coating and wear resistance in the surface of the coating, the sandwich-structured Ni60CuMo coating with the transition layer was fabricated on RuT300 by laser cladding. The microstructure, hardness, and fracture toughness for the coating were analyzed, and the effect of different loads on wear resistance was investigated. The wear-resistant layer mainly contains Ni-based solid solution, hard phase of chromium compound and some ductile Cu phases. The hardness for coating without cracks shows the stepped distribution, increasing to 381HV0.5, 419HV0.5, and 490HV0.5 in the wear layer, transition layer, and heat-affected zone, respectively. The transition layer can suppress the impact of carbon from the substrate on the hardness of the wear-resistant layer. The wear resistance of the coating demonstrates a self-adaptive enhancement effect with increasing load. As the load increases from 10 N to 30 N and 50 N, the wear rate decreases from 2.865 to 1.525 and 1 (×10⁻⁴mm³N⁻¹m⁻¹). The main wear mechanism is oxidative wear. The extruded ductile Cu phase causes the wear debris to adhere it and the compacted oxide glaze layer is formed with the high load, then the compacted oxide glaze layer isolates oxygen and reduces oxidative wear. In contrast, incomplete oxide layers at low load fail to provide effective isolation, and cracks on the subsurface serve as critical pathways for continued oxygen penetration, resulting in more severe oxidative wear.

Joining of Copper and Aluminum Alloy A6061 Plates at Edges by High-Speed Sliding with Compression

By using the joined or welded materials of dissimilar metals, the characteristics and performance of products and parts can be improved. The combination of copper and aluminum is difficult to weld. In this study, the impact joining of copper C1100 and aluminum alloy A6061-T6 plates at the edges was investigated to explore the appropriate joining conditions. The plates are joined with newly created surfaces generated by the high-speed compressive deformation with sliding motion. The shape near the interface was a tapered trapezoid with a flat top. The joining length in the plate thickness direction was shorter than the plate thickness, and notches were observed near both plate surfaces. The length became slightly longer by setting a larger top width of the C1100 plate than that of A6061-T6. The joint efficiency increased by approximately 10%. Applying the emery paper finish to the surface of the plate eliminated the non-joining result in multiple experiments. The finishing direction is effective only in the longitudinal direction of the plate. In the tensile test on the dumbbell-type specimen with reduced thickness to eliminate notches, most results showed a fracture at the C1100 portion. The estimated temperature rise of the C1100 is more than about 250 K during the impact deformation. Hence, the strength of the A6061-T6 becomes lower than that of C1100 during the process, and the softened layer of aluminum comes out under pressure, resulting in good joining performance.

Study on the effect of microstructure on toughness dispersion of X70 steel girth weld

The girth weld metal impact toughness would affect the safe operation of long transmission oil and gas pipeline. In order to further clarify toughness law of pipeline steel girth weld, the Charpy impact toughness of X70 steel girth weld at −10 °C was studied by standard impact method, and the impact energy range was determined to be 18–95 J. The impact energy range of girth welds varied significantly, and the toughness was discrete. The impact toughness of the different microstructures in the girth weld at −158 °C was studied by the small specimen impact test. The root weld metal mainly consisted of ferrite and a small amount of pearlite, and its impact toughness was low. The large effective grain size and dislocation density difference between large lath bainite (LB) and coarse granular bainite (GB) increased the strain heterogeneity during impact deformation. In fine GB, effective grain size reduction and uniform distribution of Martensite austenite (M–A) components reduced the local strain, resulting in more uniform deformation. Therefore, the sample with the fine GB had higher impact the toughness and ductile fracture mode. For the standard Charpy impact samples, the main reason for toughness dispersion was change of fine GB proportion. The fine GB proportions of P6-2, P3-3 and P3-2 were 46.7 %, 40.8 %, and 29.5 %, respectively. Simultaneously, the influence of position change on the impact energy was considered.

The effect of friction characteristics on electromagnetic impact deformation mechanism of 2A10 aluminum alloy bars

Purpose The purpose objective of this study is to identify the friction coefficient and friction effect in electromagnetic upsetting (EMU) high-speed forming process. Design/methodology/approach Based on numerical simulation and upsetting experiment of 2A10 aluminum alloy bar, the friction coefficient between contact surfaces is obtained by combining the fitting displacement distribution function and the electromagnetic-mechanical coupling numerical model, and the influence of friction effect is analyzed. Findings The maximum impact velocity and acceleration during EMU are 13.9 m/s and −3.3 × 106 m/s2, respectively, and the maximum strain rate is 7700 s−1. The functional distribution relationship between friction coefficient combination (FS, FD) and characteristic parameters [upper diameter (D1) and middle diameter (D2)] is established. The values of FS and FD are 0.1402 and 0.0931, respectively, and the maximum relative error is 2.39%. By analyzing the distribution of equivalent stress and strain, it is found that plastic deformation has obvious zoning characteristics and there is serious failure concentration in the strong shear zone. Originality/value Friction coefficient significantly affects stress or strain distributions in material forming process, but it is difficult to obtain friction coefficients through experimental tests in the high-speed forming process. In this paper, a multi-field coupling numerical model is proposed to determine friction coefficients and applied to the electromagnetic impact loading process (a high-speed forming process). Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2024-0154/

Study on the elastic impact deformation behavior and damage mechanism during the polishing process of PS@CeO2 core-shell abrasive

Discrete element simulations were carried out to investigate the elastic impact damage mechanism of PS@CeO2 core-shell abrasive (CSCAP). Aiming at understanding the deformation behavior and damage mechanism of CSCAP during the polishing process, effects of the impact velocity, impact angle on the rates of deformation and recovery deformation, stress distribution, the number of microcracks were systematically investigated. Tensile cracks formed owing to the CSCAP deformation was gradually increasing when impacting the workpiece downwards. After the CSCAP reached the maximum deformation, macroscopic cracks at the interface were extended gradually. Owing to the redistribution of the compressive force, the interface was observed to predominantly occur in shear cracks, while the shell layer was found to be distributed with tensile cracks. The number of microcracks increase with the increase in impact speed, the impact angle was within the range of 15° to 45°. This investigation enhances the comprehension of nanoscale deformation damage mechanism in CSCAP during ultra-precision machining processes.

On the role of chemically heterogeneous austenite in cryogenic toughness of maraging steels manufactured via laser powder bed fusion

Steels manufactured via Laser powder bed fusion (LPBF) usually exhibit a good synergy of strength and ductility due to their ultrafine microstructure. Yet, their toughness, in particular cryogenic toughness is intrinsically inferior as the formation of micro-voids and oxide inclusions can hardly be fully prevented during LPBF. In this study, a toughening strategy based on chemically heterogenous metastable austenite was proposed to improve the impact toughness of LPBF manufactured high strength steels. As demonstrated in a maraging stainless steel, cryogenic (-196 °C) impact toughness can be enhanced by three times without a sacrifice of strength via tailoring chemically heterogenous austenite in the strong martensitic matrix. Both experiments and molecular dynamic simulations demonstrate that upon impact deformation chemically heterogenous austenite could transform into martensite in a stepwise manner, which could not only absorb massive energy via deformation induced martensite transformation but also make a contribution to local stress mitigation, crack passivation and deflection. The chemically heterogenous austenite strategy has the potential to be utilized for improving the toughness of other high-strength steels.

Experimental study on the mechanical characteristics of a novel high-strength-and-high-toughness steel

To effectively control large deformation disasters, our team has developed a novel high-strength and high-toughness (HSHT) steel. This study aims to conduct a comparative analysis of the mechanical properties of HSHT steel and typical commercial steel under tension and impact. Testing was carried out using a universal testing machine and a self-developed drop-hammer-type longitudinal impact dynamic mechanical tester, with dynamic axial force sensors and infrared equipment utilized for monitoring. The results of the experiments are as follows: In the tensile test, HSHT steel exhibited superior performance in terms of tensile strength, elongation, and uniform deformation, particularly in radial deformation. The strength-ductility product of HSHT steel was more than two times that of typical commercial steel, indicating better energy-absorbing properties. Infrared data analysis showed that HSHT steel bars displayed uniform warming throughout their entire length. In the impact test, HSHT steel reinforcement demonstrated higher mechanical properties compared to commercial steel. Following failure, HSHT steel bars did not exhibit significant necking at the fracture site and showed a larger area of impact deformation. The axial forces experienced by the different steel bars were similar under various conditions. Data fitting analysis revealed an exponential relationship between the static tensile maximum strains of all bar types and the number of cyclic impacts. For HSHT steel bars, the number of impacts was also exponentially related to displacement, cyclic height, and energy absorbed prior to failure. Additionally, HSHT bars exhibited better uniform heating characteristics during cyclic impacts, with higher heating temperatures compared to typical commercial steels.

Residual strength assessment of a heat straightened ASTM A 7 Steel I-section member exposed to a fire event

Heat straightening is an efficient and cost-effective method of repairing steel members that have experienced impact or fire-induced deformations. Postfire investigations have shown that fire exposure can cause considerable loss of residual mechanical properties. Beyond the fire event itself, additional heat applied to the member during the straightening process can, potentially, even further modify the mechanical properties of steels. This study aims to evaluate residual mechanical behavior at zones of maximum heat-induced distortion representative of both the fire event and the heat-straightening repair of a fire-damaged steel I-section. The study further aims to independently observe heating patterns, working temperatures, and external jacking forces during heat straightening. The fire-damaged member was restrained in three-point bending with fork boundary conditions simulating service conditions for a discretely braced bridge stringer. Results revealed that the cumulative effect of both the fire and the repair caused measurable differences in mechanical properties compared with an undamaged portion of the member, but mean properties still exceeded ASTM International’s ASTM A 7 product and the AASHTO nonfracture-critical toughness requirements. Supplemental metallographic analyses revealed no measurable alteration in metallurgical phase composition or grain size of the steel, indicating that heat straightening would have been a viable repair solution to keep the member in service.

SynTissue® as a surrogate material for the human scalp

Synthetic skin produced by SynDaver®, currently used primarily in medical testing and training applications, may be suitable as a surrogate for human skin in forensic investigations. To determine how accurately the company's synthetic skin, SynTissue®, could mimic the mechanical properties of human skin, tests were conducted to measure its elastic modulus and resistance to laceration. Test results were compared to published data acquired from tensile tests conducted on human scalp and impacts with blunt objects on porcine heads. The stress vs strain relation for SynTissue® 8 N corresponded closely to that of the human scalp. Deformations similar to skin lacerations were observed when SynTissue® was subjected to blunt object impacts, at forces in the range of those reported for lacerations of cadaver and porcine heads. However, the published data are insufficient to unequivocally assess the suitability of SynTissue® for forensic investigations of lacerations. Moreover, there are features of the SynTissue® impact deformations that can provide useful information even if the laceration threshold turns out to be lower than that of human skin.

Damage behaviour of rail flash-butt welding joints under controlled impact kinetic energy

Rail welded joints are a critical component of seamless railway tracks, and they are essential for maintaining the continuity and smoothness of the tracks. However, they also represent weak points in the entire track, which makes these areas susceptible to frequent damage and rail breaks. This study employs an impact wear testing platform with controlled energy to compare and analyse the impact wear characteristics of three different locations (i.e., weld zone, heat-affected zone and base material) on the U75VG flash-butt welding joint. Results indicate significant differences in material properties, such as hardness and microstructure, within different zones of the flash welded rail joints, which leads to varying impact damage behaviours. The heat-affected zones, which are located on both sides of the weld zone, exhibit the weakest ability to resist impact deformation. Thus, these areas are the most vulnerable in the entire welded rail joint and are prone to damages, such as squat. In general, damage in different zones of the welded joint gradually evolves from plastic deformation and local pitting into fatigue wear with delamination as the main failure mechanism, while the surface of the heat-affected zone tends to develop an oxide debris layer. The distinct damages observed in different zones of the welded joint pose challenges to the problem of track irregularities. This study offers a theoretical framework for predicting the evolution of damage in welded joints.

Effect of finned configuration of circular tube based on fluid-structure coupling on hydrogen flow characteristics

Nuclear thermal propulsion has the characteristics of high specific impulse, large thrust, green and efficient, and is the primary choice of manned deep space exploration propulsion system. Because the circulating flow of propellant hydrogen in the internal pipeline of the engine is always affected by the harsh environment of high temperature and high pressure, it is very important to study the flow characteristics of hydrogen in the pipeline, the heat exchange characteristics of hydrogen and pipeline and the deformation characteristics of pipeline under heat stress. In this paper, the flow phenomena of hot hydrogen in round tubes in a laminar flow state were analyzed by numerical simulation with COMSOL Mulitiphisics6.0, and the fluid-structure coupling between hot hydrogen fluid and pipe was investigated by a multi-physics field. It is concluded that the smoother the inner wall of the pipeline is, the smaller the hydrogen flow velocity is, the smaller the surface pressure of the pipe wall is, and the smaller the fluid extrusion and impact deformation of the pipe in the typical pipe with the inner fin is. It inspires studying the application of hot hydrogen flow and pipeline configuration in nuclear thermal rocket engines, including improving heat transfer energy and uniformity.

HED zircons as a window into the solar system’s first crust: Decoupling primordial differentiation, metamorphism and impact events through textural and chemical studies

The study of Howardite-Eucrite-Diogenite (HED) meteorites provides unique insights into early planet formation and the impact events that shaped the early Solar System. However, unraveling the complex history of the HED parent body (hypothesized to be the asteroid 4 Vesta) from whole-rock samples is challenging since most HEDs are impact-related breccias comprising mixed lithic and mineral fragments that experienced variable deformation and alteration. Combining U-Pb geochronology, trace element geochemistry, and microstructural analysis of zircon can unravel magmatic, metamorphic and impact processes through time to decipher the HED parent body evolution. Here we present textural (EBSD), geochronological (207Pb/206Pb SIMS dating) and geochemical data (Th/U, REE, Ti-in-zircon thermometry) on 61 zircon grains from melt breccia eucrites, unbrecciated/monomict/polymict eucrites, howardites and diogenites. Diverse textures indicate variable histories of impact deformation and high-temperature recrystallization. Undeformed, fractured zircons preserve primary zoning (CL, Th/U, REE) indicating magmatic and metamorphic origins. At least three magmatic zircon grains (Th/U > 0.3) give 207Pb/206Pb ages of 4558–4565 Ma, suggesting primary differentiation in the parent body first million years. Twenty metamorphic zircon grains (Th/U < 0.3) date to 4420–4568 Ma, indicating prolonged thermal metamorphism from impact heating and/or crustal cooling. Impact-recrystallized granular zircon grains reveal major impacts during and just after the parent body differentiation (4500–4560 Ma), plus later events potentially linked to synchronous impacts in the Solar System (e.g. the Moon). Similarity of metamorphic and shocked zircon ages (circa 4550–4450 Ma) suggests impacts occurred for ≥100 million years after the parent body formed.